Дисертації: "Ferrite de Bismuth"

1

Moniz, S. J. A. "Growth of bismuth oxide and bismuth ferrite thin films via CVD." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1370616/.

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This thesis describes the growth of bismuth oxide (Bi2O3) and multiferroic bismuth ferrite (BiFeO3) films via chemical vapour deposition (CVD). The synthesis of a range of bismuth(III) β-diketonate complexes was carried out via a ligand-exchange reaction between [Bi(N(SiMe3)2)3] and the respective free ligand, and crystal structures of [Bi(dbm)3]2 and [Bi(acac)3] are reported. The decomposition of these complexes was studied via DSC-TGA to assess their potential as single-source precursors to Bi2O3, and the mass transport characteristics of the volatile complexes [Bi(mmp)3], [Bi(thd)3] and [Bi(OtBu)3] were studied. Bi2O3 films were grown via the LPCVD reaction of the single-source precursor [Bi(OtBu)3]; the crystalline phase (and band-gap) of the resultant films depended strongly upon the reactor conditions. Films were tested for photo-oxidation of water under UV-light, revealing high activities comparable to those of TiO2 films described previously. [Bi(dbm)3]2 was utilised as a single-source precursor to β-Bi2O3 films via AACVD, together with the growth of Pt(0) films using H2PtCl6.6H2O as a precursor. Pt-nanoparticle Bi2O3 films were grown via a ‘one-pot’ AACVD reaction of both precursors; composite Pt-Bi2O3 films were able to evolve hydrogen via the photo-reduction of water, a property not observed for films containing either Pt or Bi2O3 alone. BiFeO3 films were grown via a multi-source LPCVD reaction between [Fe(acac)3], [Bi(OtBu)3] and air, as well as via the dual-source reaction of [Bi(OtBu)3] and [Fe(OtBu)3]2 without oxidising gas, and, furthermore, via the single-source precursor [{Cp(CO)2Fe}BiCl2] using AACVD. Magnetometry revealed low temperature ferromagnetism and spin-glass behaviour, characteristic of larger particle sizes. Ferroelectric measurements revealed low polarisation but nevertheless indicated films were multiferroic at room temperature. A selection of these films were tested for photo-oxidation of water under visible-light; films displayed high photoactivities with rates in excess of those from optimised TiO2 films measured under UV-light, highlighting the potential of BiFeO3 films as strong visible-light active photocatalysts.

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2

Hatling, Oddmund. "Multiferroic, Magnetoelectric Nanoparticles : Lanthanum-substituted Bismuth Ferrite." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16315.

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In this report, 10 at% lanthanum was introduced to the perovskite structure of bismuth ferrite at the expense of bismuth through a modified Pechini wet chemical method. Green body powders were calcined at several temperatures, and the lattice parameters for each size were found by Rietveld refinement of X-ray powder diffraction data. The parameters displayed strong size-dependent properties, and the rhombohedral distortion from the cubic structure was reduced by decreased particle size. With decreasing crystallite size, the Néel temperature decreased and the cooperative cationic displacement (s - t) showed size dependence at crystallite sizes below 30 nm. A size-dependency was also observed in the Curie temperature.

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3

Liu, Yuhang. "First Principle Study of Multiferroic Bismuth Ferrite." Thesis, Uppsala universitet, Materialteori, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-364857.

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4

Skiadopoulou, Styliani. "Multiferroic behaviour of bismuth ferrite porous thin films." Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11829.

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Mestrado em Engenharia de Materiais
An enormous contribution in the scientific community of material engineering is being made by the exceptionally rapid evolution of the field of multifunctional materials. Multiferroics combine simultaneously at least two of the three ferroic properties: ferroelectricity, ferromagnetism and ferroelasticity. Magnetoelectric multiferroics’ ability of magnetic field manipulation via electric fields or vice versa can be extremely promising for information storage applications, leading to thinner, as well as flexible devices, with significantly high energetic efficiencies and elevated capacities. The aim of this work is the preparation and characterization of bismuth ferrite porous thin films, having as further objective to be able to serve as matrices for future functionalization. The strategy of this work consists of: a) dense film preparation with varying deposition velocities, b) porous film preparation with varying solution template quantities, inorganic precursor concentration and deposition velocities. Annealing temperature studies were also required, for the obtainment of the desired properties and control of microstructure. The methodologies for the film preparation in use were: a) sol-gel process, b) Evaporation Induced Self-Assembly (EISA), for the induction of porosity, and c) dip-coating technique. A series of dense films with varying deposition velocities were produced, serving as means of comparison for the porous thin films. Increasing the sol-gel deposition velocity led to increasing thickness. Piezoresponse Force Microscopy (PFM) characterization was conducted, revealing the expected ferroelectric domains. By the same technique, local piezoelectric hysteresis loops were obtained, showing increase of polarization saturation with increasing thickness. Lastly, magnetic moment measurements were carried out by the use of Superconducting Quantum Interference Device (SQUID), presenting decrease of remnant magnetization with increasing thickness. Varying template concentration was introduced in order to obtain a homogenous porous network. Homogeneity and lack of cracks in the films were successfully achieved, by decreasing solution template mass, for a given solution concentration. Thermal treatment studies revealed loss of porous network ordering at elevated annealing temperatures, required for the obtainment of crystallization and enhanced multiferroic properties. Local piezoelectric hysteresis loops showed increase of the effective piezoelectric coefficient with increasing thickness. SQUID characterization presented increasing remnant magnetization with increasing porosity. Lastly, increasing inorganic precursors concentration resulted in better control of porosity order and increase in the piezoelectric coefficient.
Uma enorme contribuição na comunidade científica da Engenharia de Materiais tem sido feita pela evolução excecionalmente rápida no âmbito dos materiais multifuncionais. Os multiferróicos combinam simultaneamente pelo menos duas das três propriedades ferróicas: ferroeletricidade, ferromagnetismo e ferroelasticidade. Os multiferróicos magnetoelétricos que permitem a manipulação do campo magnético através do campo elétrico e vice versa são extremamente promissores para aplicações de armazenamento de informação, levando a dispositivos mais finos e flexíveis com eficiência energética significativamente mais alta e elevadas capacidades. O objetivo deste trabalho é a preparação e caracterização de filmes porosos de ferrite de bismuto, com vista a serem capazes a uma futura funcionalização. A estratégia deste trabalho consiste: a) preparação de filme denso variando a velocidade de deposição, b) preparação de filme poroso variando o template da solução concentração do precursor inorgânico, e velocidades de deposição. Os estudos sobre temperatura de calcinação são também necessários, para a obtenção das propriedades requeridas e o controlo da microestrutura. As metodologias para a preparação dos filmes foram: a) sol-gel, b) Evaporation Induced Self-Assembly, para a indução da porosidade, e c) dip-coating. Foi preparada uma série de filmes densos variando a velocidade de deposição, servindo como meio de comparação para os filmes porosos. Aumento da velocidade de deposição resulta em aumento da espessura dos filmes. Foi utilizada a caracterização por piezoresponse force microscopy (PFM), revelando domínios ferroelétricos como esperado. Pela mesma técnica, foram obtidas curvas de histerese piezoelétricas locais mostrando o aumento da saturação da polarização com o aumento da espessura. Por fim, as medidas dos momentos magnéticos foram obtidos através do Superconducting Quantum Interference Device (SQUID), apresentando uma diminuição da magnetização remanescente com o aumento da espessura. A variação da concentração do template foi introduzida de modo a obter uma porosidade homogénea. A homogeneidade e ausência de fissuras nos filmes foi conseguida com sucesso pela diminuição da massa do template da solução, para uma determinada concentração da solução. Os estudos do tratamento térmico revelou a perda da porosidade ordenada para temperaturas mais elevadas, necessárias para a obtenção da cristalização e melhoria das propriedades multiferróicas. As curvas de histerese piezoelétrica local mostraram um aumento do coeficiente efetivo piezoelétrico com o aumento da espessura. A caracterização por SQUID apresentou um aumento da magnetização remanescente com o aumento da porosidade. Por fim, o aumento da concentração dos precursores inorgânicos resulta em um melhor controlo da ordem da porosidade e aumento do coeficiente piezoelétrico.

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5

Palizdar, Meghdad. "Preparation and characterization of textured bismuth ferrite based ceramics." Thesis, University of Leeds, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590464.

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There are many reports in the literature describing the effect of texture on the magnetic and electric properties of materials. Texture is used to provide an enhancement in various properties, compared to random orientation, for example an increase in piezoelectric coefficient, or remnant magnetization. In this work, molten salt and tape casting techniques were employed to synthesis textured bismuth ferrite based ceramics. The fabrication of highly-oriented polycrystalJine ceramics of Bi5Feo.SCOo.5 Ti JOl5 (BFCT), prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets is reported. Electron backscatter images show a secondary phase within the ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from scanning electron microscopy was estimated at < 2 % by volume, below the detection limit of X-ray diffraction. By fabricating textured BFCf, it can be shown that the observed ferromagnetic response is dominated by the secondary phase; although the material is textured, the magnetic response is anisotropic, proving that the BFCT matrix is not ferromagnetic. The templated grain growth techniq ue was used to synthesis textured 60BiFeO-40PbTiO or 60:40BFPT. Both Aurivillius templates (Bi4 Ti30 12 and PbBi4Ti40) and perovskite templates (BaTiO), SrTi03 and 0.4(NaI2BiIl2)Ti03-0.6PbTi03) were used to prepare 60:40BFPT. Only BaTiO) templates were successful in imparting texture on the BFPT matrix. In the case of SrTiO, a reduction in Curie temperature was observed (Tc = 350°C) due to the substitution of Sr+. Aurivillius templates resulted in high Curie temperatures (610 °C). However, the resulting ceramics show low remanent polarization, while SrTi03 and BaTi03 templated ceramics show higher remanent polarizations of36 and 30 llc/cm2 , respectively. There are many repolts in the literature describing the effect of texture on the magnetic and electric properties of materials. Texture is used to provide an enhancement in various properties, compared to random orientation, for example an increase in piezoelectric coefficien t, or remnant magnetization. In this work, molten salt and tape casting techniques were employed to synthesis textured bismuth ferrite based ceramics. The fabrication of highly-oriented polycrystalJine ceramics of Bi5Feo.SCOo.5 Ti JOl5 (BFCT), prepared via molten salt synthesis and uniax ial pressing of high aspect ratio pl atelets is reported. Electron backscatter images show a secondary phase within the ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from scanning electron microscopy was estimated at < 2 % by volume, below the detection limit of X-ray diffraction. By fabricating textured BFCf, it can be shown that the observed ferromagnetic response is dominated by the secondary phase; although the material is textured, the magnetic response is anisotropic, proving that the BFCT matrix is not ferromagnetic. The templated grain growth techniq ue was used to synthesis textured 60BiFeOJ-40PbTiOJ or 60:40BFPT. Both Aurivillius templates (Bi4 Ti30 12 and PbBi4 Ti40 IS) and perovskite templates (BaTiO), SrTi03 and 0.4(NaII2BiIl2)Ti03-0.6PbTi03) were used to prepare 60:40BFPT. Only BaTiO) templates were successful in imparting texture on the BFPT matrix. In the case of SrTiOJ, a reduction in Curie temperature was observed (Tc = 350°C) due to the substitution of Sr+. Aurivillius templates resulted in high Curie temperatures (610 °C). However, the resulting ceramics show low remanent polarization, while SrTi03 and BaTi03 templated ceramics show higher remanent polarizations of36 and 30 llc/cm2 , respectively. Synchrorron measurements clearly show textured 6O:40BFPT using BaTi03 templates. Polari sation and strain field measurements were used to show that the resulting material wa<; ferroelectric, with a Ec of 6 kV/mm, a Pr of 30 llClcm2 and a total strain of 0.09%. Vibrating sample magnetometry was used, and showed magnetic anisotropy in the material fabricated using BaTiOJ templates. The coercive field of 177 Oe and maximum magnetization of 1.43 emu/g was obtained when magnetic field applied nonna] to the cast direction. By applying the magnetic field along (0 the cast direction, a far higher coercive field of 908 Oe, and lower maximum magnetization of 0.29 emu/g was reali zed. The reaction of Ba with the BFPT matrix leads to the generation of ferromagnetic ordering, as opposed to the anti ferromagnetic ordering observed in BFPT prepared using conventional processing. In summary, the template grain growth technique has been used to generate textured Ba-doped BFPT. The resulting materia] is both ferrom agnetic and ferroelectric at room temperature.

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6

Turner, Stuart Lee. "The structure of bismuth ferrite - lead titanate (BiFeO3 - PbTiO3)." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507885.

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7

Gupta, Rekha. "Magnetoelectric coupling in multiferroic bismuth ferrite based composite nanostructures." Thesis, IIT Delhi, 2017. http://localhost:8080/iit/handle/2074/7057.

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8

Burnett, Timothy Laurence. "Growth and charaterisation of bismuth ferrite lead titanate single crystals." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.487709.

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Bismuth ferrite lead titanate (BFPT) shows potential in high temperature piezoelectric and ferroelectric applications as well in the emerging field of multiferroic research. Single crystals of (BFPT) have been grown for the first time using the flux growth method.

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9

Shenton, John Kane. "First-principles investigations of structure-function relationships in bismuth ferrite." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10057684/.

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The simplicity of the basic perovskite structure belies a seemingly boundless potential for novel phenomena and technological applications. The ferroelectric perovskites, in particular, can have complex and subtle relationships between their crystal structures and functional properties. Understanding such structure-function relationships is a central theme of this work. In this work, advanced computational approaches are used to gain insight into key structure-function relationships in the multiferroic perovskite, bismuth ferrite (BFO). Density functional theory (DFT) has proven to be an immensely valuable tool in the study of condensed matter. However, techniques beyond standard DFT are often required to deal with the strongly localised electronic states in materials like BFO. In the first part of this thesis, we conduct a systematic study of a commonly used correction to DFT: DFT+U. We focus on the effect of the U parameter on the conduction band minimum (CBM) and valence band maximum (VBM). We find drastic changes to the location and curvature of the CBM in particular. Specifically, we find a surprising inversion in the ordering of the Fe t2g and eg manifolds at the CBM when U exceeds 4 eV. We therefore suggest caution when employing large values of U to calculate optoelectronic properties. In the second part of this work, motivated by the prospects of BFO-based photovoltaics, we investigate the influence of crystal structure on charge carrier effective masses. We begin by comparing the effective masses of several known phases of BFO, finding orders of magnitude differences between them. The strain-induced tetragonal phase emerged from this comparison as having the promising combination of a large spontaneous polarisation and relatively light charge carriers. Through a systematic decomposition of geometric relationships between different phases of BFO, we identify key physical influences on effective masses. We suggest that these insights could be exploited to improve photovoltaic efficiency. In the final part of this thesis, we enter the realm of designer materials. The creation and characterisation of atomically sharp interfaces between different complex oxides has proven to be an exciting and fruitful area of research in recent years. We investigate superlattices made up of repeating lanthanum aluminate (LAO) and BFO layers. By simply varying the thickness of the BFO layer, we found that one could tune the tetragonality, spontaneous polarisation and band gap of the superlattices. We also predict the formation of two-dimensional (2D) electron and hole gases at opposing interfaces above a critical thickness of BFO. The ferroelectric origin of the 2D gases, together with an emergent magnetism, suggests that this system may be a promising source of novel multiferroic functionality. In particular, we suggest the possibility of switching the 2D electron and hole gases via an external electric field.

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10

Stevenson, Timothy James. "Magnetic and electric properties of bismuth ferrite lead titanate ceramics." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1371/.

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Solid solutions of multiferroic BiFeO3 doped with ferroelectric PbTiO3 (BFPT) can be prepared by conventional mixed oxide processing to produce a range of polycrystalline ceramics ranging throughout the xBiFeO3 - (1-x)PbTiO3 series. Sintered ceramics are shown to exhibit mixed tetragonal (P4mm) and rhombohedral (R3c) phase perovskite distortions from 0.4 ≤ x < 0.75, where at x ~ 0.75 a morphotropic phase boundary exists and compositions x > 0.75 are entirely rhombohedral. From extensive use of neutron diffraction experiments, the phase coexistence is attributed to compensation for the internal strain induced upon cooling through the ferroelectric Curie point from cubic, to the distorted tetragonal perovskite phase (ܿ/ܽ = 1.17). This drives a further partial transformation to the (~4 %) lower volume rhombohedral phase as a relief mechanism. Increasing the sinter temperature and fast cooling (> 900 °C/hr) sees the monolithic samples x ≤ 0.7 disintegrate to various levels of particulate size, when a critical grain size is exceeded (7 μm), which in turn is inversely proportional to the grain boundary fracture energy. The magnetic properties studied using high resolution powder diffractometry of these two states present G-type antiferromagnetism (AFM) in both the rhombohedral and tetragonal phases; but with Tn above ambient temperature for R3c, and below for P4mm for all compositions except x = 0.3. Compositions below this PbTiO3 rich solution are never observed to support antiferromagnetic order, as the dilution of magnetic iron ions exceeds the percolation threshold via substitution with titanium ions. The rhombohedral phase is shown to exhibit an incommensurate, modulated magnetic order, with a propagation vector perpendicular to the magnetization vector, which decreases in periodicity with increasing bismuth ferrite, from 840 Å for x = 0.75. At room temperature, transforming the paramagnetic tetragonally distorted powder to a G-type AFM rhombohedral phase, is observed with the application of hydrostatic pressure. Evident from neutron experiments, using the Pearl instrument at ISIS, full transformation can be achieved with moderate pressures of 0.77 GPa, effectively ‘switching’ on the magnetic order. The monolithic samples were used at 250 K to observe the changes in simultaneous structural and G-type antiferromagnetic properties as a function of applied electric field (0 to 10 MVm-1) for the most piezoelectrically active samples, around the MPB composition (x = 0.7), using neutron diffraction at the Berlin neutron scattering centre; instrument E2. An observed increase in rhombohedral phase occurs with the application of electric field from peak analysis, which relates to a proportional increase in observed antiferromagnetic intensity (5 %). These two behaviours are proposed to be linked by the internal strain developed within the system, from increased polarisation forcing a partial phase transformation from the tetragonal to the rhombohedral phase which can support the antiferromagnetic order at room temperature.

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11

Cressoni, Chiara <1995&gt. "Modified nanostructured Bismuth Ferrite thin films for application in photoelectrocatalysis." Master's Degree Thesis, Università Ca' Foscari Venezia, 2019. http://hdl.handle.net/10579/16018.

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The thesis project is focused on the synthesis and characterization of nanostructured bismuth ferrite, BiFeO3 (BFO), thin films with enhanced photoelectrocatalytic properties. Photoelectrocatalytic materials are semiconductors that are able to catalyze water splitting processes or other reactions under sunlight irradiation. They can, through the absorption of photons, create electron/hole pairs which can be exploited to carry out electrochemical reactions. BFO is a very promising perovskite-type material with an optical band gap that fits well with the sunlight irradiation in the visible region. Since most of the conventional photocatalyst like TiO2 is limited by a wide band gap and a UV light absorption, the BFO material is an interesting visible light driven photoactive material for solar energy conversion. The main disadvantages of such material are poor efficiency and high variability in the photoelectrocatalytic performance. BFO’s performance depends on structure, defects, phase, electronic properties, which are directly connected with the synthetic methodology. In this thesis a sol-gel synthesis has been optimized in order to prepare highly reproducible thin films, that could be directly applied to a device, with modified structure and improved photoelectrocatalytic performance. Moreover, in order to achieve sensitization in the Near Infrared Region where pure BFO is not active, a composite nanomaterial has been developed. Previously prepared nanoparticles with peculiar optical properties have been dispersed in a BFO matrix and the optical and structural characterization have been carried out to correlate the enhancement of photoelectrocatalytic properties with the modification caused by the nanoparticles doping.

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12

Wang, Naigang. "Multiferroic Bismuth Ferrite-Lead Titanate and Iron-Gallium Crystalline Solutions: Structure-Property Investigations." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33854.

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Recently, multiferroics-defined as materials with coexistence of at least two of the ferroelectric, ferroelastic and ferromagnetic effects-have attracted enormous research activities. In this thesis, the structure and properties of multiferrioic BiFeO3-x%PbTiO3 and Fe-x%Ga crystalline solutions were investigated. First, the results show that modified BiFeO3-PbTiO3 based ceramics have significantly enhanced multiferroic properties, relative to BiFeO3 single crystals. The data reveal: (i) a dramatic increase in the induced polarization; and (ii) the establishment of a remnant magnetization by a breaking of the translational invariance of a long-period cycloidal spin structure, via substituent effects. In addition, temperature dependent magnetic permeability investigations of BiFeO3-xPbTiO3 crystalline solutions have shown that aliovalent La substitution results in a significant increase in the permeability. Second, room temperature high-resolution neutron and x-ray diffraction studies have been performed on Fe-x%Ga crystals for 12Master of Science

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13

Manjunath, B. "Structural and magnetic properties of Bi and Fe sites co-substituted bismuth ferrite." Thesis(Ph.D.), CSIR - National Chemical Laboratory, Pune, 2018. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4532.

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14

Sena, Wellington Adriano Fernandes. "Propriedades estruturais e controle da estequiometria de filmes finos de BiFeO3 /." Ilha Solteira, 2019. http://hdl.handle.net/11449/190753.

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Orientador: Eudes Borges de Araújo
Resumo: O objetivo do trabalho foi estudar as propriedades estruturais dos filmes finos de ferrita de bismuto (BFO) ao se adicionar excesso de nitrato de ferro ao invés de nitrato de bismuto conforme muitas referências na literatura vêm praticando com a intenção de obter um BFO puro. Filmes finos de BFO foram preparados sobre substratos Pt/TiO2/SiO2/Si(100) usando o método de Pechini pertencente a rota química sol-gel polimérica. Foram produzidos filmes de estequiometria nominal e de variação de 2, 4, 6, 8, 10 e 12 mol% de excesso de nitrato de Ferro. O processo de síntese dos filmes passou por quatro deposições, quatro pirólises a 300 ºC por 20 minutos e cristalização a 600 ºC por 40 minutos. As propriedades físicas dos filmes foram investigadas usando técnicas de MEV, DRX, Raman e EDS. Rietveld foi usado para calcular os parâmetros de rede e o modelo de Williamson-Hall foi usado para calcular o tamanho do cristalito e o microstrain. Resultados do DRX revelaram o aparecimento da fase secundária Bi2O3, ela aparece quando há o excesso de bismuto. Resultados do EDS confirmam o excesso de Bi. A técnica de EDS apontou uma maior At% do bismuto em relação ao ferro em todas as amostras, sendo que, a de 12 mol% foi a que apresentou características mais próxima de uma estequiometria desejável para a produção de um BFO puro.
Abstract: The objective of this work was to study the structural properties of bismuth ferrite (BFO) thin films by adding excess iron nitrate instead of bismuth nitrate as many references in the literature have been practicing with the intention of obtaining a pure BFO. BFO thin films were prepared on Pt / TiO2 / SiO2 / Si (100) substrates using the Pechini method belonging to the polymeric sol-gel chemical route. Films of nominal stoichiometry and variation of 2, 4, 6, 8, 10 and 12 mol% of iron nitrate excess were produced. The synthesis process of the films went through four depositions, four pyrolysis at 300 ºC for 20 minutes and crystallization at 600 ºC for 40 minutes. The physical properties of the films were investigated using SEM, XRD, Raman and EDS techniques. Rietveld was used to calculate lattice parameters and the Williamson-Hall model was used to calculate crystallite size and microstrain. XRD results revealed the appearance of the secondary phase Bi2O3, it appears when there is excess bismuth. EDS results confirm excess Bi. The EDS technique showed a higher At% of bismuth in relation to iron in all samples, and the 12 mol% was the one that presented characteristics closer to a desirable stoichiometry for the production of a pure BFO.
Mestre

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15

Kavanagh, Christopher M. "Synthesis and structure-property relationships in rare earth doped bismuth ferrite." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3555.

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There has been significant interest in BiFeO₃ over the past decade. This interest has focused on the magnetic and electrical properties, which in the long term may prove useful in device applications. This thesis focuses on the synthesis, electrical characterisation, and structural origin of the electrical properties of rare earth doped bismuth ferrite. Two systems have been studied: BiFeO₃ doped with lanthanum and neodymium (Bi₁₋ₓREₓFeO₃ RE= La, Nd). Specific examples have been highlighted focusing on a detailed structural analysis of a lanthanum doped bismuth ferrite, Bi₀.₅La₀.₅FeO₃, and a neodymium analogue, Bi₀.₇Nd₀.₃FeO₃. Both adopt an orthorhombic GdFeO₃-type structure (space group: Pnma) with G-type antiferromagnetism. Structural variations were investigated by Rietveld refinement of temperature dependent powder neutron diffraction using a combination of both conventional “bond angle/bond length” and symmetry-mode analysis. The latter was particularly useful as it allowed the effects of A-site displacements and octahedral tilts/distortions to be considered separately. This in-depth structural analysis was complemented with ac-immittance spectroscopy using the multi-formulism approach of combined impedance and modulus data to correlate structural changes with the bulk electrical properties. This approach was essential due to the complex nature of the electrical response with contributions from different electroactive regions. The structural variations occur due to a changing balance between magnetic properties and other bonding contributions in the respective systems. This results in changes in the magnitude of the octahedral tilts, and A-site displacements giving rise to phenomena such as negative thermal expansion and invariant lattice parameters i.e., the invar effect. More specifically, analysis of Bi₀.₅La₀.₅FeO₃ highlights a structural link between changes in the relative dielectric permittivity and changes in the FeO₆ octahedral tilt magnitudes, accompanied by a structural distortion of the octahedra with corresponding A-site displacement along the c-axis; this behaviour is unusual due to an increasing in-phase tilt mode with increasing temperature. The anomalous orthorhombic distortion is driven by magnetostriction at the onset of antiferromagnetic ordering resulting in an Invar effect along the magnetic c-axis and anisotropic displacement of the A-site Bi³⁺ and La³⁺ along the a-axis. This contrasts with the neodymium analogue Bi₀.₇Nd₀.₃FeO₃ in which a combination of increasing A-site displacements in the ac-plane and decrease in both in-phase and anti-phase tilts combine with superexchange giving rise to negative thermal expansion at low temperature. The A-site displacements correlate with the orthorhombic strain. By carefully changing the synthesis conditions, a significant change in bulk conductivity was observed for a number for Bi₁₋ₓLaₓFeO₃ compositions. A series of Bi₀.₆La0.₄FeO₃ samples are discussed, where changes in the second step of the synthesis result in significantly different bulk conductivities. This behaviour is also observed in other compositions e.g. Bi₀.₇₅La₀.₂₅FeO₃. Changes in the electrical behaviour as a function of temperature are discussed in terms of phase composition and concentration gradients of defects. Activation energies associated with the conduction process(es) in Bi₁₋ₓLaₓFeO₃ samples, regardless of composition, fall within one of two broad regimes, circa. 0.5 eV or 1.0 eV, associated with polaron hopping or migration of charge via oxygen vacancies, respectively. The use of symmetry-mode analysis, in combination with conventional crystallographic analysis and electrical analysis using multi-formulism approach, presents a new paradigm for investigation of structure-property relationships in rare earth doped BiFeO₃.

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16

Bennett, James Thomas. "Development of bismuth ferrite derived piezoelectric ceramics for high temperature applications." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7473/.

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The foundations of this project lay in the authors research into the xBiFeO3-(1-x)(K0.5Bi0.5)TiO3 ceramic system. A broad pseudocubic region was identified where x = 0.4-0.3, these compositions produced large electric-field induced strains (>0.3%) due to the presence of polar nanoregions that are easily switched by an applied electric field, however, these return to a random order upon removal of the field. Positive-up negative-down (PUND) showed that ferroelectric switching was reduced in the pseudocubic region and synchrotron studies with an applied electric-field in-situ demonstrated predominantly reversible domain switching. Solid-solutions based upon the (1-x-y)BiFeO3-x(K0.5Bi0.5)TiO3-yPbTiO3 ternary system have been fabricated by conventional mixed oxide processing, this system is the primary focus of this thesis. Structural analysis using XRD established that long-range crystallographic order was present above a critical PbTiO3 concentration, in addition a broad mixed symmetry region was identified comprised of tetragonal and rhombohedral symmetries. The ferroelectric Curie temperature was between 410-590 ºC. Conventional ferroelectric and piezoelectric ordering was observed with the use of strain and polarization-field measurements. Rayleigh analysis was used to quantify the intrinsic and extrinsic contributions, a critical c/a ratio was identified at 1.045 with domain switching limited above this. Synchrotron x-rays with ex-situ electric-fields allowed for a more detailed structural analysis, selected compositions demonstrated significant phase changing behaviour. The room temperature tetragonal c/a ratio across the mixed symmetry region, Curie temperature, and piezoelectric d33 were found to correlate strongly with the PbTiO3 concentration in a number of compositions. This work demonstrates a number of important results that have wider implications. Ternary and pseudo-quaternary systems have recently been subject to large amounts of research as many of the possible binary systems have been exhausted. This has led to a raft of materials with reported high electric-field induced strains, these are often electrostrictive or have limited operating temperatures. The partial substitution of PbTiO3 promotes long-range non-centrosymmetric order, which leads to increased piezoelectric activity and TC.

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17

Salih, Jalal Mohammed. "Quantitative atomic resolution characterisation of internal interfaces in doped bismuth ferrite." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/8283/.

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Since bismuth ferrite-based perovskites display magnetic ordering as well as ferroelectric behaviour, they have been widely researched due to the possibility to fabricate multiferroic devices. This thesis is focused on investigating structures formed in bismuth ferrite (BFO) as a consequence of Ti doping using atomic resolution transmission electron microscopy (TEM). This is performed both using the negative spherical aberration (NCSI) imaging technique in TEM and scanning transmission electron microscopy (STEM) with simultaneous dark and bright field imaging. A quantitative study was made of the diference between high resolution TEM (HRTEM) and high resolution STEM (HRSTEM) for quantitative polarisation mapping around antiphase boundaries (APBs) is observed and reported. Although similar trends in the structures are found in the two techniques, quantitative diferences are noted. For HRTEM, using NCSI gives 60% lower polarisation values in comparison to HRSTEM in the case studied here. It is shown that the sample tilt has no in uence on the polarisation measurements in this case as the direction of the sample tilt in our case is perpendicular to the direction of polarisation. It is shown that the ultra-thin sample used in HRTEM had a reduced polarisation due to the effects of surfaces, but that also the polarisation was underestimated from the images due to one oxygen column appearing in the images at a position slightly displaced from its real position due to the effects of electron channeling in the material. For the case of HRSTEM, it was found that the polarisation was overestimated due to a similar effect, where an oxygen atom image is slightly displaced from the column position in the opposite direction at this specifc sample thickness. Thus, it is clear that the use of simulations is essential to any atomic resolution quantifcation of polarisation by either technique. In addition to this, , the structure and chemistry of the crosses and corners on APBs were determined using a combination of high angle annular dark field (HAADF) combined with electron energy loss spectroscopy spectrum imaging (EELS-SI) in STEM. The 3D structures of the APB cross structure were fully determined and these were verified by multislice frozen phonon image simulations. It was suggested on the basis of the structure of some of the edge-sharing octahedral structural units in this cross that they would support a permanent magnetic ordering, since their structure was similar to that of maghemite. In analysing this structure, the advantages of non-rigid registration (alignment of a sequence of short exposure images as well as removing local distortions in each image prior to summation) for removing line noise distortions from STEM images are investigated quantitatively. Two APB corners were also investigated using NCSI HRTEM and HRSTEM. Whilst some details of each structure were impossible to determine unambiguously, most parts of these APB corners have structural units similar to those in steps and in the APB cross. It should also be noted that the two APB corners show some detailed differences in structure suggesting that there is a range of possible structures on such antiphase boundaries, but all constructed from a limited number of structural units.

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18

Ruette, Benjamin Thibault. "Induced Phase Transition in Magnetoelectric BiFeO3 Crystals, Thin-layers and Ceramics." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/42638.

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Bismuth ferrite (BiFeO₃) is a magneto-electric material which exhibits simultaneously ferroelectric and antiferromagnetic properties. We have used high-field electron spin resonance (ESR) as a local probe of the magnetic order in the magnetic range of 0-25 Tesla. With increasing magnetic field, an induced transition has been found between incommensurately modulated cycloidal antiferromagnetic and homogeneous magnetized spin state. The data reveal a number of interesting changes with increasing field, including: (i) significant changes in the ESR spectra; (ii) hysteresis in the spectra near the critical field. We have analyzed the changes in the ESR spectra by taking into account the magnetic anisotropy of the crystal and the homogeneous anti-symmetric Dzyaloshinsky-Moria exchange. We have also investigated phase induced transition by epitaxial constraint, and substituent and cystalline solution effects. Variously oriented BiFeO₃ epitaxial thin films have been deposited by pulsed laser deposition. Dramatically enhanced polarization has been found for (001)c, (110)c, and (111)c films, relative to that of BiFeO₃ crystals. The easy axis of spontaneous polarization lies close to (111)c for the variously oriented films. BiFeO₃ films grown on (111)c have a rhombohedral structure, identical to that of single crystals. Whereas, films grown on (110)c or (001)c are explained in terms of an epitaxially-induced transition between cycloidal and homogeneous spin states, via magneto-electric interactions. Finally, lanthanum modified BiFeO₃-xPbTiO₃ crystalline solutions have been found to have a large linear magneto-electric coefficient, ∝p. The value of ∝p (2.5x10⁻⁹ s/m or C/m²-Oe) is ∼10x greater than that of any other material (cg., Cr₂O₃ ∼2.5x10⁻¹⁰ s/m), and many order(s) of magnitude higher than unmodified BiFeO₃ crystals. The data also reveal: (i) that ∝p is due to a linear coupling between polarization and magnetization; and (ii) that ∝p is independent of dc magnetic bias and ac magnetic field. We show that the ME effect is significantly enhanced due to the breaking of the transitional invariance of a long-period spiral spin structure, via randomly distributed charged imperfections.
Master of Science

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19

Oliveira, Felipe Fernandes de. "Deposição de filmes BiFeO3 via spray pirólise e caracterização microestrutural e de propriedades elétricas e ópticas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/131385.

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Este trabalho investigou a deposição de filmes finos de ferrita de bismuto (BFO) através da técnica spray pirólise utilizando sais inorgânicos como precursores em diferentes solventes e silício como substrato, visando a deposição em menor temperatura e a obtenção de diferentes morfologias de superfície. Para tanto, foram utilizados água, etilenoglicol e etanol/butil carbitol (1:1) como solventes na preparação da solução a ser aspergida. Foram realizadas deposições com diferentes temperaturas do substrato: 200, 250, 300 e 350ºC para cada solvente utilizado. A deposição de filmes BFO em baixas temperaturas (200ºC) favoreceu a formação de filme. Para o solvente etilenoglicol (maior ponto de ebulição), verifica-se a formação de filmes porosos, já para o solvente etanol/butil carbitol (1:1) foi verificada a formação de filmes densos com a presença de trincas. As análises termogravimétricas (ATG) e termodiferenciais (ATD) foram realizadas para os filmes como-depositados a 200ºC com diferentes solventes. Após a deposição, as amostras foram tratadas termicamente a 550ºC por 1h, visando a formação da fase cristalina BiFeO3 com estrutura romboédrica. Os filmes foram analisados por difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). Os resultados mostraram a obtenção da fase cristalina do BiFeO3 após o tratamento térmico a 550ºC/1h com a presença de fase secundária. As imagens de MEV evidenciaram a formação de filmes independente do solvente utilizado para a temperatura de 200ºC. Contudo, o aumento da temperatura promoveu a formação de partículas sobre o substrato e não uma formação contínua de filme, evidenciada pela composição elementar medida através de espectroscopia por energia dispersiva de raios X (EDX). A caracterização elétrica dos filmes foi realizada utilizando espectroscopia de impedância (EI) em função da temperatura, sendo observada maior condutividade para o filme depositado com etilenoglicol. A fase BFO não estequiométrica evidenciada por DRX pode explicar as diferentes condutividades elétricas mensuradas por EI quando utilizado diferentes solventes. As propriedades ópticas foram medidas utilizando-se espectroscopia de reflectância difusa, encontrando-se um band gap entre 2,23 – 2,26 eV.
This research investigated the deposition of thin films of bismuth ferrite (BFO) on silicon substrate using the spray pyrolysis technique based on inorganic salts as precursors. For this purpose water, ethylene glycol and ethanol/butyl carbytol (1:1) were used as solvents to prepare the solution for spraying. The depositions were carried out with different substrate temperatures for each solvent used: 200, 250, 300 and 350ºC. The film deposition at low temperatures (200°C) promotes the formation of cracks due to the arrival of the liquid state from droplets sprayed by the atomizer. When using solvent ethanol/butyl carbytol (1:1) the formation of dense films was verified for the different depositions. The thermal gravimetric (TGA) and differential thermal analysis (DTA) were performed for the as-deposited films at 200°C with different solvents for the study of possible reactions of thermal decomposition. The BFO films were heated at 550°C for one hour aiming to the formation of the crystalline state BiFeO3 with rhombohedral structure. The films were analyzed by Xray diffraction (XRD) and scanning electron microscopy (SEM) before and after treatment. The XRD showed the crystalline state obtained after the heat treatment at 550°C/1h. It was observed the formation of non-stoichiometric composition on the film. The SEM images showed formation of films regardless of the solvent used for the temperature to 200°C. However, the increase temperature promotes the formation of particles on the substrate. Applying the ethylene glycol solvent the formation of porous films appeared, since for ethanol/butyl carbytol (1:1) was observed the formation of dense films with the presence of cracks. The electrical characterization of the films will be performed using impedance spectroscopy (IS) coupled to a furnace in order to vary the temperature of the measures. The film deposited with ethylene glycol presents a major electrical conductivity than films deposited using ethanol/butyl carbytol or water. This behavior can be associated with a non-stoichiometric composition of BFO. Moreover, the optical properties were obtained by diffuse reflectance spectroscopy. The films present a band gap between 2.23 and 2.26 eV, approximately.

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20

Wang, LiQiu. "Quantitative three dimensional atomic resolution characterisation of non-stoichiometric nanostructures in doped bismuth ferrite." Thesis, University of Glasgow, 2013. http://theses.gla.ac.uk/4364/.

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Over the last decade, the lead-free, environmentally-friendly multiferroic material, BiFeO3 (BFO), has once again received tremendous attention from researchers, not only for its fundamental properties, but also for its potential applications such as novel devices that can be written by an electric field and read by a magnetic field. However, one of the most important limitations for applications is the high leakage current in pure materials. Doping has proved to be an effective way to reduce the leakage current caused by the electron hopping between Fe2+ and Fe3+. In this work, a series of Nd3+ and Ti4+ co-doped BFO compositions have been studied using a combination of atomic resolution imaging and electron energy loss spectroscopy in STEM, especially concentrating on nanostructures within the Bi0.85Nd0.15Fe0.9Ti0.1O3 composition, as nanostructures can play an important role in the properties of a crystal. Two types of novel defects – Nd-rich nanorod precipitates and Ti-cored anti-phase boundaries (APBs) are revealed for the first time. The 3D structures of these defects were fully reconstructed and verified by multislice frozen phonon image simulations. The very formation of these defects was shown to be caused by the excess doping of Ti into the material and their impact upon the matrix is discussed. The nanorods consist of 8 atom columns with two Nd columns in the very center forming the Nd oxide. Density functional theory calculation reveals that the structures of the nanorod and its surrounding perovskites are rather unusual. The Nd in the core is seven coordinated by oxygen while the coordination of B site Fe3+ at its surroundings are just five-coordinated by oxygen due to the strain between the nanorod and the surrounding perovskite. The APB is nonstoichiometric and can be treated as being constructed from two main structural units - terraces and steps. Within the terraces, Ti4+ occupy the centre of the terrace with Ti/Fe alternately occupying either side of the terrace. As for the step, this is constructed from iron oxide alone with a structure similar to g-Fe2O3, and Ti is completely absent. Quantitative analysis of the structure shows the APB is negatively charged and this results in electric fields around the APBs that induce a local phase transformation from an antiferroelectric phase to a locally polarised phase in the perovskite matrix. Based on this thorough investigation of these defects, a new ionic compensation mechanism was proposed for reducing the conductivity of BiFeO3 without the complications of introducing non-stoichiometric nanoscale defects.

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21

Qaisar, Sayyed Adam. "Fatigue and high temperature behaviour of the La-doped bismuth-ferrite lead-titanate system." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5556/.

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For the past fifty years, lead zirconate titanate (PZT) has been the material of choice for the piezoelectric industry with piezoelectric materials showing promise in their applicability to smart devices and structures, from adaptive optics to ultrasonics and sonar. The longevity and reliability of PZT is, as with any commercial material, a topic that is well documented with reported operating lifetimes as large as 109 cycles. However PZT is severely limited in the type of thermal environment it can sustainably operate in, with maximum operating temperatures conservatively set around 150°C for commercial materials a new material is required for use in thermally hostile environments. The basic aim of this research was to investigate the performance of 3% La-doped BFPT as a device at high temperatures, fields and stresses in comparison to equivalent PZT materials and further understanding of fatigue in both materials - essential for use of either as a commercially viable device. As no such, readily accessible, apparatus for testing ferroelectric ceramics existed it was essential to first develop the capability before experimentation could begin. Upon development of a suitable apparatus, BFLPT and PZT fatigue studies were conducted and the fatigue as a function of domain contributions investigated using weak-signal measurements in bulk materials. Furthermore, using weak-signal measurements a study of domain behaviour at temperature was sought to give insight into the fundamental behaviour of ferroelectric materials at elevated temperatures - something previously only investigated using the likes of synchrotron facilities, and highlighted previously unobserved contribution changes occurring during material ageing.

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22

Abdul, Hadi Zeinab. "Terahertz emission spectroscopy of multiferroic bismuth ferrite : insights into ultrafast currents and phonon dynamics." Electronic Thesis or Diss., Le Mans, 2024. http://www.theses.fr/2024LEMA1030.

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La technologie térahertz (THz) a suscité un intérêt significatif dans la communauté scientifique en raison de sa position unique dans le spectre électromagnétique, complétant le gap entre les régions des micro-ondes et de l'infrarouge. Cette radiation est non ionisante et peut pénétrer divers matériaux sans les endommager, ce qui la rend très attirante pour de nombreuses applications potentielles. Les avancées récentes dans la technologie des lasers ultra-rapides ont élargi l'exploration du rayonnement THz à un large éventail de technologies passionnantes. Elle est désormais utilisée dans des domaines tels que la médecine pour de nouvelles techniques d'imagerie, en spectroscopie pour l'analyse des matériaux, dans les technologies de l'information et de la communication pour le transfert de données plus rapide, et même dans la sécurité, l'agriculture, le contrôle de qualité et la science des matériaux fondamentaux.Par conséquent, le développement de sources THz efficaces et réglables est devenu un défi au sein de la communauté THz pour développer davantage ces applications, motivant l'exploration de nouveaux matériaux et mécanismes d'émission THz. Dans mon projet de doctorat, j'ai exploré un nouvel émetteur THz : le matériau multiferroïque le plus connu, le ferrite de bismuth (BiFeO3). Ce matériau multiferroïque est particulièrement intéressant en raison de ses propriétés multiferroïques distinctives. Le BiFeO3 présente à la fois une large polarisation ferroélectrique et un ordre antiferromagnétique à température ambiante, offrant une interaction unique des ordres ferroélectriques et magnétiques et faisant de ce matériau un candidat prometteur pour la génération de THz.En utilisant un montage de spectroscopie d'émission THz que j'ai construit, avec sa détection électro-optique, j'examine l'émission THz de trois échantillons de BiFeO3 distincts. Le premier avec une polarisation dans le plan, un autre avec une polarisation hors plan, et un troisième présentant deux domaines avec deux différentes orientations de polarisation. Cette technique permet l'observation et l'analyse directes du rayonnement THz émis par ces échantillons suite à l'excitation laser au-dessus du gap.Les études expérimentales impliquent une analyse détaillée des signaux THz émis par les échantillons de BiFeO3 dans des conditions expérimentales variées. En variant les longueurs d'onde de la pompe, les orientations des échantillons, les directions de polarisation de la lumière de la pompe, et la puissance de la pompe, nous pouvons explorer comment ces facteurs influencent l'émission THz. Ensuite, nous séparent la dynamique ultra-rapide des porteurs (courant ultra-rapide) et les vibrations du réseau (phonons optiques) contribuant à ce signal THz émis. Enfin, en analysant leur réponse aux changements des paramètres expérimentaux, nous pouvons approfondir notre compréhension des mécanismes physiques contribuant à ces dynamiques ultra-rapides et à l'émission THz dans BiFeO3
Terahertz (THz) technologies have attracted significant interest in the scientific community due to their unique position in the electromagnetic spectrum, bridging the gap between the microwave and infrared regions. This radiation is non-ionizing and can penetrate various materials without causing damage, making it highly attractive for numerous potential applications. Recent advances in ultrafast laser technology have expanded the exploration of THz radiation into a wide range of exciting technologies. It’s now being used in fields like medicine for new imaging techniques, in spectroscopy for analyzing materials, in information and communication technology for faster data transfer, and even in security, agriculture, quality control and fundamental material science. Consequently, the development of efficient and tunable THz sources has become a major focus within the THz community to expand these applications further, motivating the exploration of new materials and emission mechanisms. In my PhD project, I have explored a promising new THz emitter: the well-known multiferroic material ‘Bismuth Ferrite’ (BiFeO3). This multiferroic material is particularly interesting due to its distinctive multiferroic properties. BiFeO3 exhibits both a large ferroelectric polarization and a antiferromagnetic order at room temperature offering a unique interplay of ferroelectric and magnetic orders and making this material a promising candidate for THz generation. Using a THz emission spectroscopy setup that I constructed, with its electro-optical sampling detection, I examine THz emission from three distinct BiFeO3 samples. First one with in-plane polarization, another with out-of-plane polarization, and a third presenting striped domains with two orientations of polarization. This technique allows for the direct observation and analysis of THz radiation emitted by these samples upon above gap laser excitation. The experimental investigation involves a detailed study of the THz transient signals emitted from the BiFeO3 samples under varying experimental conditions. By varying the pump wavelengths, sample orientations, directions of pump light polarization, and pump power levels, we can explore how these factors influence the THz emission. Following this, we extract the carrier dynamics (ultrafast current) and lattice vibrations (optical phonons) contributions to this THz transient. And finally, by analyzing their response to experimental parameters changes, we can have a deeper understanding of the physical mechanisms contributing to these ultrafast dynamics and THz emission in BiFeO3

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23

Haneberg, Dag Håkon. "A Finite-Size Study on Samarium-Substituted Bismuth Ferrite : Multiferroic and Lead-Free Piezoelectric Materials." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16311.

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Multiferroic materials combine two or more ferroic orders such as ferroelectricity, ferromagnetism and ferroelasticity. They have a great interest for the development of the next generations of digital electronic memory devices. Bismuth ferrite has shown to posess both ferroelectric and magnetic order at room temperature, which makes it both scientifically and comercially interesting.The negative impact on the environment by using lead in mass-produced units has made development of lead-free piezoelectric materials for use in sensors, actuators and transducers prioritized and samarium substituted bismuth ferrite has shown to posess a piezoelectric response high enough to be considered for commercial applications. In this project work, 10mol% samarium substituted bismuth ferrite, Bi_{0.9}Sm_{0.1}FeO_{3}, powders have been synthesized using a wet-chemical method and calcined to a range of temperatures to achieve a range of nanocrystalline sizes in the powders. These powders has been investigated using X-ray diffraction (XRD), Rietveld refinement and differential scanning calorimetry (DSC). The powders have also been milled, pressed and sintered to pellets for ferroelectric and piezoelectric testing. The crystal structure was found to belong to the R3c group as for bismuth ferrite, BiFeO_{3}, but the unit cell geometry is changed slightly, and the ferroelectric polarizability is lowered in the case of samarium substitution. This fact is interesting regarding piezoelectricity by thereby increasing the ability to achieve a higher piezoelectric response. No results were achieved from ferroelectric and piezoelectric measurement due to the conductivity found in the sintered pellets were too high, probably due to secondary sillenite phases found in the material. There has been found a finite size effect of a decrease in unit cell volume and tetragonality, of which the decrease in volume is contradictory to the expectations. There is also clear finite size effects on the decrease of cooperative displacement of cations, a measure for the polarization, and for the lowering of the ferroelectric phase transition temperature. The finite size effect for the ferroelectric phase transition has not been reported before. The magnetic phase transition temperature also show a decrease as a clear finite size effect. A linear relationship between electric polarization and magnetic ordering has also been observed in this project. The results from this project contributes to the understanding of material properties of BiFeO_{3} and derived compositions by an investigation of substitution effects and finite size effects. The results presented here motivates further research on these materials.

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24

Khan, Mikael Ali. "Preparation and properties of bismuth ferrite-lead titanate thin films prepared by pulsed laser deposition." Thesis, University of Leeds, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485633.

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Development of ferroelectric thin films has been a subject of intensive investigation in recent years due to their promise in nextÃ‚Â· generation electronic devices. This report encompasses anÃ‚Â· initial investigation into the pulsed laser deposition of thin films of bismuth ferrite-lead titanate (l-x)BiFe03-xPbTi03 (BFPT) on platinized silicon (Pt/Si) substrates. The work presented lays down optimised processing conditions for the preparation of BFPT thin films on Pt/Si substrates and presents an understanding of structure-property relationships of this material system thereby providing a firm platform to go forward and exploit this material in various thin film applications, particularly those requiring large remanent polarizations. The growth conditions were optimized by changing a range of process .parameters such as background oxygen pressure, substrate temperature and target to substrate distance which have a critical influence on the film structure and properties. The film structure was studied using X-ray diffraction and scanning electron microscopy. The ferroelectric properties have been presented in terms of typical polarization-field P-E hysteresis behaviour, in conjunction with leakage current measurements and impedance spectroscopy. Investigation into the electrical properties indicates a large increase in the remanent polarization close to the morphotropic phase boundary, making these compositions very attractive for commercial thin film applications e.g. ferroelectric memories.

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25

Yao, Situ. "Preparation and Magneto-optical Effect of Ferrite-based Composites and Thin Films." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215554.

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26

Nguyen, Lucie. "Approche du frittage et du co-frittage de matériaux céramiques et métalliques pour l'élaboration par le procédé d'impression jet d'encre de composants magnétiques." Limoges, 2013. http://www.theses.fr/2013LIMO4005.

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Ce travail est consacré à l’étude du frittage de matériaux céramiques et métalliques en vue de leur co-frittage pour l’élaboration d’un composant magnétique mis en forme par un procédé d’impression jet d’encre. L’étude et la compréhension du frittage du matériau isolant (à base de silice) avec ou sans additifs de type TiO2, Bi2O3, ZnO se sont appuyées sur l’identification in situ par MEBE et DRX des transformations de phases et des mécanismes de densification intervenant au cours du traitement thermique. Il a été notamment montré que ces additifs pouvaient jouer le rôle soit de modificateur soit de formateur du réseau de la silice vitreuse et conduire ainsi à de fortes variations de la température de cristallisation et de densification. Les cinétiques de densification et l’amplitude des retraits des matériaux isolant, conducteur et magnétique étant très différentes, plusieurs voies d’amélioration ont été préconisées en vue de leur cofrittage : dopage du matériau conducteur, température de calcination du matériau magnétique. . . . Ces choix ont permis, à terme, la réalisation de composants bimatériaux mis en forme par impression jet d’encre aux designs proches de celui du composant final
This work deals with the study of the sintering of ceramic and metallic materials to allow their co-sintering for the development of a magnetic component shaped by ink-jet printing. The study and understanding of the sintering of the dielectric material (composed of silica) with or without additives such as TiO2, Bi2O3, ZnO relied on the in situ characterizations by ESEM and XRD of the phase transformations, the mechanisms of densification occurring during the heat treatment. It has been shown that these additives could act either as former or modifier of the vitreous silica network and lead to large variations in the crystallization température and densification. The densification kinetics and shrinkage amplitude of the dielectric, conductive and magnetic materials are very different, several improvement possibilities were advocated for their co-sintering: doping of the conductive material, calcination température of the magnetic material. . . . These solutions allowed the élaboration of bimaterial components shaped by ink-jet printing with designs close to the one of the final component

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27

Lepoittevin, Christophe. "Nouvelles ferrites de strontium présentant des structures complexes : synthèse et caractérisation structurale." Caen, 2006. http://www.theses.fr/2006CAEN2063.

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Ce travail de thèse est consacré à la recherche de nouvelles phases dans le système A-Sr-Fe-O (A = Bi ou Pb) riche en fer et à leur caractérisation structurale à l’aide de techniques telles que la microscopie électronique en transmission et la diffraction des rayons X sur poudre et sur monocristal. Le composé à l’origine de cette étude est le composé Sr4Fe6O13- dont la structure, déjà décrite il y a quelques années, consiste en l’alternance d’une simple couche perovskite [Sr2Fe2O6] avec une couche complexe [Sr2Fe4O7-delta]. Ce travail de thèse a permis de mettre en évidence et de comprendre des mécanismes structuraux complexes qui avaient été peu étudiés auparavant, puis d’exprimer cet oxyde sous la forme Fe2(Sr2)FeO6. 5-delta apparenté aux structures de type 2201. Les substitutions effectuées sur les sites Sr ont permis d’isoler quatre nouvelles phases. La première est l’oxyde Bi4Sr14Fe24O56, dont la caractérisation structurale a conduit à une description sous forme de doubles couches perovskite [(Bi,Sr)2Fe2O6]2 alternant avec une couche complexe [(Bi,Sr)2Fe4O7-delta]. Ce composé s’exprime sous la forme Fe2(Bi0. 69Sr1. 31)SrFe2O9. 5±delta/2, apparentée aux structures de type 2212. Une nouvelle phase obtenue par les substitutions sur le site Sr est la ferrite Pb4Sr13Fe24O53 dont la structure, dite en terrasses, résulte de l’intercroissance de quatre motifs 2201 avec trois motifs 2212 suivant la direction [203] de la sous-maille. Les deux dernières phases synthétisées et caractérisées structuralement sont les perovskites ordonnées déficitaires Bi1/3Sr2/3FeO2. 67 et Bi0. 5Ca0. 5FeO2. 75. Tous ces composés sont antiferromagnétiques associés à un comportement électrique de type semi-conducteur

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28

Smith, Thomas. "Studies of p-type semiconductor photoelectrodes for tandem solar cells." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/14522.

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Photoelectrodes and photovoltaic devices have been prepared via multiple thin film deposition methods. Aerosol assisted chemical vapour deposition (AACVD), electrodeposition (ED), chemical bath deposition (CBD) and doctor blade technique (DB) have been used to deposit binary and ternary metal oxide films on FTO glass substrates. The prepared thin films were characterised by a combination of SEM (Scanning Electron Microscopy), powder X-ray diffraction, mechanical strength tests and photochemical measurements. Nickel oxide (NiO) thin films prepared by AACVD were determined to have good mechanical strength . with a photocurrent of 7.6 μA cm-2 at 0 V and an onset potential of about 0.10 V. This contrasted with the dark current density of 0.3 μA cm-2 at 0 V. These NiO samples have very high porosity with crystalline columns evidenced by SEM. In comparison with the AACVD methodology, NiO films prepared using a combination of ED and DB show good mechanical strength but a higher photocurrent of 24 μA cm-2 at 0 V and an onset potential of about 0.10 V with a significantly greater dark current density of 7 μA cm-2 at 0 V. The characteristic features shown in the SEM are smaller pores compared to the AACVD method. Copper (II) oxide (CuO) and copper (I) oxide (Cu2O) films were fabricated by AACVD by varying the annealing temperature between 100-325°C in air using a fixed annealing time of 30 min. It was shown by photocurrent density (J-V) measurements that CuO produced at 325 °C was most stable and provided the highest photocurrent of 173 μA cm-2 at 0 V with an onset potential of about 0.23 V. The alignment of zinc oxide (ZnO) nano-rods and nano-tubes fabricated by CBD have been shown to be strongly affected by the seed layer on the FTO substrate. SEM images showed that AACVD provided the best seed layer for aligning the growth of the nano-rods perpendicular to the surface. Nano-rods were successfully altered into nano-tubes using a potassium chloride bath etching method. NiO prepared by both AACVD and the combined ED/DB method were sensitized to absorb more of the solar spectrum using AACVD to deposit CuO over the NiO. A large increase in the photocurrent was observed for the p-type photoelectrode. These p-type photoelectrode showed a photocurrent density of approximately 100 μA cm-2 at 0 V and an onset potential of 0.3 V. This photocathode was then used as a base to produce a solid state p-type solar cell. For the construction of the solid state solar cells several n-type semiconductors were used, these were ZnO, WO3 and BiVO4. WO3 and BiVO4 were successfully produced with BiVO4 proving to be the optimum choice. This cell was then studied more in depth and optimised by controlling the thickness of each layer and annealing temperatures. The best solid state solar cell produced had a Jsc of 0.541 μA cm-2 (541 nA) and a Voc of 0.14 V, TX146 made up of NiO 20 min, CuFe2O4 50 min, CuO 10 min, BiVO4 27 min, using AACVD and then annealed for 30 min at 600°C.

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29

Kirsch, Andrea [Verfasser], Thorsten M. [Akademischer Betreuer] Gesing, Reinhard X. [Gutachter] Fischer, and Götz [Gutachter] Eckold. "Multiferroic bismuth ferrates : Synthesis, structure-property relationships and phase transformations / Andrea Kirsch ; Gutachter: Reinhard X. Fischer, Götz Eckold ; Betreuer: Thorsten M. Gesing." Bremen : Staats- und Universitätsbibliothek Bremen, 2018. http://d-nb.info/1170321089/34.

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30

Velez, Emersson Eduardo Espinosa. "Síntese e estudo das propriedades estruturais, morfológicas e elétricas do composto Bi25FeO39 e suas potenciais aplicações." reponame:Repositório Institucional da UFABC, 2016.

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Orientador: Prof. Dr Carlos Ivan Henao Osorio
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2016.
Neste trabalho, apresentamos novos resultados sobre segurança de protocolos de distribuição quântica de chave de duas vías (TWQKD por suas iniciáis em inglês) que utilizam estados não ortogonáis. Trabalhamos no cenário de protocolos para os quais o pós-processamento é feito com comunicação clássica de uma via e não há pre-processamento. O análise de segurança é implementado com tecnicas que permitem cubrir conjuntos de protocolos bastante amplos. Desse jeito, providenciamos uma nova prova de segurança para um protocolo TWQKD recentemente proposto [32] e pesquisamos a possibilidade de superar seu desempenho. Este protocolo é determinista, o que signica que o receptor pode decodicar os bits codicados com probabilidade igual a um. Mostramos que só há um protocolo TWQKD desse tipo (não reportado na literatura até onde sabemos) com o potencial de ter uma fração secreta maior e em consequência ser mais robusto ao ruído. Além disso, é argumentado que a fração secreta correspondente podería ser a mesma do protocolo "six-state" [9]. Por outro lado, analizamos o desempenho de protocolos TWQKD quando o ruído do canal de comunicação pode depender das polarizações especícas dos estados transmitidos. Encontramos que, para certas famílias de protocolos e uma quantidade de ruído dada, a informação potencialmente ltrada é limitada superiormente pela associada com um canal despolarizante. Adicionalmente, táis protocolos incluem opera ções de "pre-codicação" que poderíam contribuir a esta melhora no caso de ruído assimétrico. Denimos também um parâmetro para caracterizar a eciência de protocolos TWQKD, associado à fração de qubits que o receptor pode decodicar; em concordância, este parâmetro alcança o máximo valor para protocolos deterministas. Discute-se como uma alta eciência pode na prática melhorar fatores como a taxa de bits secretos e a qualidade da estimação do ruído.
We present new results concerning security of Two-Way Quantum Key Distribution (TWQKD) protocols that employ non orthogonal states (e.g. LM05 [22]). We work within the scenario where the classical post-processing is performed with one-way classical communication and there is no pre-processing. The security analysis is carried out with techniques that allow to cover quite broad sets of protocols. In this way, we give a new security proof for a recently proposed TWQKD protocol [32] and investigate the possibility of outperforming it. This protocol is deterministic, meaning that the receiver can decode the encoded bits with probability one. We show that there is only one TWQKD protocol of this kind (non reported in the literature as far as we know) with the potential to have a larger secret fraction and consequently be more robust against noise. Furthermore, it is argued that the corresponding secret fraction could be the same of the 6-State protocol [9]. On the other hand, we analyze the performance of TWQKD protocols when the noise of the communication channel may depend of the particular polarization states being transmitted. We find that, for certain families of protocols and a given amount of total noise, the potentially leaked information is upper bounded by the associated to a depolarizing channel. Moreover, such protocols include "pre-encoding" operations that could contribute to this enhancement in the asymmetric noise case. We also define a parameter to characterize the Efficiency of QKD protocols, referring to the fraction of qubits that the receiver is able to decode; accordingly, this parameter achieves the maximum value for deterministic protocols. It is discussed how a high efficiency can in practice improve factors like the secret key rate and the quality of the noise (or error) estimation.

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31

Gonçalves, Lucas Fabrício. "Desenvolvimento de filmes finos multiferróicos de BiFeO3 modificadas com Ca com potencial aplicação em memórias de multiplos estados /." Guaratinguetá, 2018. http://hdl.handle.net/11449/157086.

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Orientador: Alexandre Zirpoli Simoes
Banca: José Vitor Candido de Souza
Banca: Mauricio Antonio Algatti
Banca: Francisco Moura Filho
Banca: Filiberto González Garcia
Resumo: Os elementos de memórias de múltiplos estados nos quais a informação pode ser armazenada tanto nos estados de polarização quanto no estado de magnetização espontânea do elemento, podem ser obtidos, através da fabricação de filmes finos texturizados de BiFeO3 (BFO) dopados com Cálcio, sobre eletrodo de (Pt/TiO2/SiO2/Si), visando otimizar as propriedades ferroeletromagnêticas. O método Pechini ou percursores poliméricos, depositados por "Spin-Coating", é relativamente de fácil controle e baixo custo para a deposição de filmes finos texturizados. O cristal do BiFeO3 possui uma estrutura perovskita distorcida em um sistema romboédrica, mas em formato de filme fino encontramos uma fase pseudo tetragonal favorável as propriedades de memorias de múltiplos estados, como a diminuição da degradação, aumento da polarização espontânea e remanescente, diminuição na corrente de fuga, diminuição do tempo de resposta ao impulso, crescimento epitaxial, controle de vacâncias de oxigênio e diminuição de fases secundarias. Tudo isso é atingido, através de variações das resinas, controlando a volatização excessiva do Bismuto e de parâmetros no crescimento do filme, como, o tempo e temperatura de cristalização, da quantidade de dopante Ca, na variação de diferentes eletrodos óxidos de base para produção do filme fino. Apesar das excelentes propriedades dos filmes finos de BiFeO3 (BFO), dois sérios problemas são comumente encontrados para imediata aplicação deste material em memórias multiferróica... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The multi-state memory elements in which the information can be stored in both the polarization states and the spontaneous magnetization state of the element can be obtained by the production of calcium-doped thin films of BiFeO3 (BFO) on electrode (Pt / TiO2 / SiO2 / Si), in order to optimize ferroelectromagnetic properties. The Pechini method or polymer precursors, deposited by Spin-Coating, is relatively easy to control and low cost for the deposition of textured thin films. The crystal of the BiFeO3 has a perovskite structure distorted in a rhombohedral system, but in thin film format we find a pseudo tetragonal phase favorable to the properties of memories of multiple states, such as the decrease of the degradation, increase of the spontaneous and remaining polarization, decrease in the current reduction of impulse response time, epitaxial growth, control of oxygen vacancies and decrease of secondary phases. All of this is achieved through variations of the resins, controlling the excessive volatilization of Bismuth and parameters in the growth of the film, such as the time and temperature of crystallization, the amount of dopant Ca, in the variation of different base oxides electrodes for production of the thin film. Despite the excellent properties of the BiFeO3 (BFO) thin films, two serious problems are commonly encountered for the immediate application of this material in multiferroic memories: high current density, resulting in Fe (Fe3 + to Fe2 +) valence fluctuatio... (Complete abstract click electronic access below)
Doutor

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32

Valette, Pascale. "Dynamique de paroi de domaines magnetiques dans des grenats ferrimagnetiques." Paris 6, 1987. http://www.theses.fr/1987PA066654.

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Etude des oscillations de parois de domaines magnetiques de couches de grenats substitues (gdbipr)::(3)(alfe)::(5)o::(12) et bi::(3)(algafe)::(5)o::(12) par effet faraday a 6328 a et sous un champ magnetique d'une frequence allant jusqu'a 50mhz. L'intensite lumineuse transmise est mesuree en fonction de la frequence et de l'intensite du champ applique. Deux modeles de parois sont correles aux resultats experimentaux. Un modele de paroi non isolee sans ligne de bloch est en accord avec les resultats experimentaux

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33

Peixoto, Marina Manuela Vieira. "Preparação e caracterização de fibras e nanotubos de BiFeO3 e FeNbO4." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/15732.

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Mestrado em Engenharia Física
Esta dissertação teve como objetivo a produção e caracterização física de fibras e nanotubos de BiFeO3 e FeNbO4. Para o desenvolvimento destes materiais utilizou-se a técnica de fusão com laser (LFZ), o método sol-gel (Pechini) e o método de poros absorventes. As amostras obtidas foram sujeitas a uma caracterização estrutural por difração de raios-X e espetroscopia de Raman, morfológica por microscopia electrónica de varrimento e elétrica por medidas de constante dielétrica. Os resultados obtidos com a técnica de difração de raios-X mostraram que o gel com tratamento a 750 ºC é polifásico. Para conseguir produzir nanotubos escolheu-se o LaCoO3 como material alternativo. Usando a técnica de fusão de zona com laser (LFZ) obtiveram-se fibras de BiFeO3, FeNbO4 e compósitos de BiFeO3+FeNbO4. Com esta técnica foram crescidas fibras a várias velocidades (5, 10, 25, 50, 100 e 200 mm/h), tendo os resultados obtidos com a difração de raios-X evidenciado que todas as amostras obtidas são polifásicas, sendo a amostra de 10 mm/h para o BiFeO3 e a de 5 mm/h para o FeNbO4 as que apresentam melhores propriedades. As amostras de 5 mm/h de todos os compósitos são aquelas que possuem menor quantidade de segundas fases e portanto foram alvo de estudo mais aprofundado. A caracterização dielétrica permitiu verificar que todas as amostras apresentam fenómenos de relaxação dielétrica. Verifica-se também que para o BiFeO3 a constante dielétrica é superior na amostra crescida à velocidade de 10 mm/h, para o FeNbO4 é superior na amostra crescida a 5 mm/h e nos compósitos a amostra com 75% de BiFeO3 e 25% de FeNbO4 apresenta um comportamento diferente das restantes, eventualmente devido à sua microestrutura singular.
In this work, BiFeO3 and FeNbO4 fibers and nanotubes were prepared and characterized. The samples were obtained using three different preparation techniques: laser floating zone technique (LFZ), sol-gel method (Pechini) and the wetting pore method. Structural characterization of the samples was made using the X-ray diffraction (XRD) and Raman spectroscopy techniques, morphologic characterization by scanning electron microscopy (SEM) and electrical characterization by impedance spectroscopy. The XRD patterns showed that the BiFeO3 gel heat-treatment at 750 °C is polycrystalline. To produce nanotubes, by the wetting pore method, LaCoO3 was used as an alternative material. With the LFZ technique, BiFeO3 and FeNbO4 fibers and BiFeO3 + FeNbO4 composites were prepared. The fibers were grown at various pulling speeds (5, 10, 25, 50, 100 and 200 mm/h), and the XRD patterns demonstrated that all samples are polycrystalline. The BiFeO3 samples growth at 10 mm/h and the FeNbO4 samples growth at 5 mm/h were chosen to be analysed electrically. The composite samples growth at 5 mm/h are those having the least amount of secondary phases, and therefore were subjected to further studies. The dielectric characterization shown that all the samples have a dielectric relaxation phenomenon, thermally activated. It was also verifyed that for the BiFeO3 sample the dielectric constant is higher for the growth speed of 10 mm/h and for the FeNbO4 is higher for the grown speed of 5 mm/h. The composite sample 75% BiFeO3-25% FeNbO4 (% wt) behaves differently from the others, possibly due to its unique microstructure.

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34

Kumari, Akanksha. "Synthesis of Bismuth Ferrite and La –doped Bismuth ferrite by auto combustion technique." Thesis, 2012. http://ethesis.nitrkl.ac.in/3764/1/akanksha_thesis.pdf.

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BiFeO3 is a multiferroic compound which has varied application in sensors and actuator. It shows both ferroelectric and antiferromagnetic property. In the present work BiFeO3 and La-doped BiFeO3 were synthesized by auto combustion technique using glycine as fuel. Glycine to nitrate ratio was kept at 0.1. Phase pure powder can be prepared at 500oC. Synthesized powder was characterized by X-ray diffraction. DSC-TG was used to find out the thermal behavior of synthesized gel and agglomeration tendency and morphology of powder were studied by SEM. La substitution greatly modified the structure of BiFeO3.

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35

Hsiu-JungYen and 顏秀容. "Effects of Cobalt Substitution on Bismuth Ferrite." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/30354049848539278314.

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碩士
國立成功大學
材料科學及工程學系碩博士班
98
Cobalt doped bismuth ferrite were synthesized by both solid state reaction and RF magnetron sputtering. In the solid state sintering process, the formation of BiFeO3 phase was often accompanied by the appearance of some secondary phases like Bi2Fe4O9 and Bi25FeO40. To avoid the problem, various sintering conditions were tried in order to get the most pure phase possible and then, the remaining trace of any secondary phase was washed away using some acid solution. It was found that the relative amount of the secondary phase, Bi2Fe4O9, was reduced by the Co doping. Similar sintering process was used to make the Co doped BiFeO3 targets for the RF magnetron sputtering of thin film samples. Under the optimum growth parameters, the films of pure BiFeO3 phase could be grown on the Pt coated silicon and the conductive FTO glass substrates, without the presence of any secondary phase. 　　The absorption spectra of Co-doped BiFeO3 films were measured by the UV-Vis spectrometry, from which the band gap was calculated to be 2.79 eV, almost exactly the same as the theoretical value for the un-doped pure BiFeO3. Photoluminescence spectra were also measured and a number of broad emission peaks were observed over the wavelength range 380-489 nm, among which the 450 nm emission came from the inter-band transition and the 469 nm emission was probably due to the transition from the Bi2+ defect level to the valence band. The origin of other emissions is not clear yet. In the electric conduction measurements, the resistivity of the BiFeO3 samples was found to decrease with the increasing temperature. The Arrhenius plots of conductivity vs. temperature showed that there existed at least two activation energies, arising from the defect or dopant energy levels inside the band gap. However, these two energy levels seemed not to be relevant to the unknown emissions observed in the photoemission spectra. In the magnetic measurements, the vibration sample magnetometry was employed to measure the M-H curves, which showed that both the saturation magnetization and the coercivity increased with the Co doping level. Thermal gravity analysis under applied magnetic field showed that the magnetization of the Co doped samples disappeared at 400 ?C, manifesting that it could not possibly come from the magnetic secondary phases such as CoFe2O4 (TC= 520 ?C), Fe3O4 (Tc= 585 ?C) and ?-Fe2O3 (Tc= 590 ?C). It was more likely that the Co doping somehow modified the spin arrangements in BiFeO3.

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36

Chih-WeiLai and 賴至緯. "Formation mechanism and dielectric behaviorof bismuth ferrite." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/78933898113177666205.

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Анотація:

碩士
國立成功大學
材料科學及工程學系碩博士班
98
BiFeO3 (BFO) is a potential material in the multiferroic materials. It exhibits ferroelectric ordering and antiferromagnetic ordering at room temperature. But there are many problems to overcome, such as second phase and large leakage current. In the previous study by other reseachers point out that the poor hysteresis loop is due to the large leakage current.In this study, we present a simple wet chemical route for obtaining single phase BiFeO3 powders.The influence on leakage current and ferrocelectric behavior by changing process parameter.Moreover ,we compare BFO by three different stoichiometric to discuss the formation mechenism of the second phase.We can see the different results by measuring P-E curve in different frequency and electric field.

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37

Kisku, Momata. "Surfactant Assisted Autocombustion Synthesis Of Bismuth Ferrite." Thesis, 2009. http://ethesis.nitrkl.ac.in/354/1/final_project_report-Bishmuth_Ferrite_pdf.pdf.

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In this work, bismuth ferrite powders has been synthesized by glycine nitrate auto-combustion method with addition of ammonium lauryl sulfate (anionic) and triton-X (non-ionic) surfactant. The precursor solutions were prepared from ferric and nickel nitrates. The effects of the surfactant on crystallite size has been investigated by XRD techniques. The results showed that addition of surfactant to the starting solution affected the crystallite size in the final product

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38

Ying-HaoWang and 王盈皓. "The Effects of Nickel Substitution on Bismuth Ferrite." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/20251920478389202766.

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39

Asmita, Kumari. "Investigation of Multiferroic Properties of Scandium Substituted Bismuth Ferrite." Thesis, 2013. http://raiith.iith.ac.in/829/1/PH11M02.pdf.

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40

Lu, Yi-Hsien, and 呂奕賢. "Nanoscale Characterization of Bismuth Ferrite Films by Scanning Probe Microscopy." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/00021545914933836056.

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Анотація:

碩士
國立清華大學
材料科學工程學系
93
Bismuth ferrite (BiFeO3, BFO), a multiferroic material possessing both ferroelectric and several magnetic orders at room temperature, is studied by scanning probe microscopy (SPM) in this dissertation. Nanoscale ferroelectric properties including domain distribution, local hysteresis, and local poling are explored by piezoresponse force microscopy (PFM), one of the analyzing tools based on SPM. The magnetic response after an electrical poling is also studied by combining PFM and magnetic force microscopy (MFM), an analyzing tool to investigate nanoscale magnetic domains based on SPM. BFO thin films were produced by magnetron sputtering at 350 �aC. With Pt/Ti/SiO2/Si substrates, BFO films showed good ferroelectricity with obvious hysteresis behavior and piezoelectric coefficients as high as 50 pm/V. However, with LNO/Pt/Ti/SiO2/Si substrate, unstable piezoresponse signal was shown. Direct domain writing using PFM on BFO films was successfully executed over large regions and on single grains. Different voltages were pre-biased at certain areas to show different polarities. A large voltage pulse was also added on a single domain to show reversed polarization. However, the magnetic response after an electrical poling was not observed due to the interference of an electrostatic force.

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41

Wang, Dan, and 王丹. "Doped Bismuth Ferrite-based Perovskite Type Cathode Materials for IT-SOFCs." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/35886765639739263603.

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Анотація:

碩士
國立臺灣大學
材料科學與工程學研究所
104
The effects of nickel, cobalt and manganese doping in bismuth-based ferrite perovskite (Bi0.7Sr0.3FeO3-δ) used as cathode of solid oxide fuel cells have been investigated in this study. The cathode powders were synthesized by EDTA-citric acid method. The phase purity of synthesized perovskites were analyzed by X-ray Diffraction (XRD). The solubility limit of Ni was 3 at%, while Mn can substitute for Fe at least 50 at% in BSF. Electrical conductivity by 2-probe and 4-probe DC methods showed that the 50 mol% doping of Mn on B-site improved the electrical conductivity significantly. The oxygen nonstoichiometry was analyzed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) to reveal the deficiency of oxygen and ionic conductivity in the ferrites. The ionic conductivity of BSF was 4.21 x10-3 S.cm-1 at 800 oC. Anode disk of 300 μm thick coated with thin layer (μm layer thickness) of electrolyte by spin-coating method. The polarization resistance and contact resistance of the half-cell with an 8YSZ-N flat layer and cathode sintered by different sintering temperatures were analyzed by electrochemical impedance spectra analysis (EIS). Finally, the optimal cathode (Bi0.7Sr0.3Fe0.5Mn0.5O 2.88-0.034+20 SDC) was assembled to a full cell and the maximum power output was 119 mW.cm-2 at 800 oC.

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42

Fan, Cheng-Li, and 范振豊. "Electric property and Photovoltaic behavior of ferroelectric bismuth ferrite thin films." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/39208185784334191366.

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43

Das, Krishnendu. "Application Of Bismuth Titanate And Bismuth Ferrite Based Binary/Ternary Heterostructure Nanomaterials Towards Photocatalytic Degradation Of Agrochemical Contaminants." Thesis, 2022. http://ethesis.nitrkl.ac.in/10428/1/2022_PhD_KDas_516CY1016_Application.pdf.

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In this thesis, the facile synthesis and photocatalytic application of bismuth titanate and bismuth ferrite based binary and ternary heterostructure materials has been presented for visible light assisted degradation of agrochemical contaminants with strong endocrine disrupting properties. Initially, suitable combustion synthesis routes were designed for phase pure synthesis of Bi4Ti3O12, Bi2Fe4O9 and Bi20TiO32/Bi4Ti3O12 composites. The synthesized complex oxides were integrated with metal sulfide nanoparticles to prepare binary/ternary p-n and Z-scheme heterostructure materials with improved optical absorption and enhanced photoelectochemical features. The photocatalytic application of the synthesized heterostructure materials were evaluated for photodegradation of pesticides/herbicides/insecticides and water pathogens under visible light irradiation. The detailed mechanistic study and evaluation of degradation pathway was carried out to understand the mechanism of photocatalytic action. Bi4Ti3O12MCPA degradationDiazinon degradationEndosulfan degradationBi2Fe4O9Sulfamethoxazole degradationPhenyl urea herbicides degradationBacterial Inactivation A series of CuS/Bi4Ti3O12 p-n heterojunction materials were synthesized by a two-step process. Initially, the Aurivillius phase Bi4Ti3O12 (BT) was synthesized by a facile combustion route using urea as a fuel. The Bi4Ti3O12 was subsequently modified by deposition of CuS (5-20 wt%) using a hydrothermal route to prepare the heterojunction materials. The methods of synthesis and calcination temperature were important factors which influenced the morphology, particle size and phase purity of Bi4Ti3O12 material. The heterostructure materials exhibited hierarchical flower like structure consisting of ultrathin CuS nanosheets and BT nanoflakes. HRTEM and microstructural study revealed microscopic close interaction between the two phases. The optical and photoelectrochemical measurement study suggested significant improvement in visible light absorption (400-800 nm) and charge carrier separation due to heterojunction formation. The CuS/Bi4Ti3O12 materials showed excellent photocatalytic activity for aqueous phase degradation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicide under visible light (> 95 % degradation in 3 h). The rate constant for CuS/Bi4Ti3O12 materials was 4.5 times higher than the pure BT material towards MCPA degradation. The OH and O2– radicals were identified as the reactive species, the formation of which was confirmed by spectrometric method using terephthalic acid and nitroblue tetrazolium as molecular probes. Further, the combustion synthesized Bi4Ti3O12 material was hybridized with SnS2 to prepare Z-scheme SnS2/Bi4Ti3O12 heterostructure photocatalyst materials. The SnS2 nanoparticles (10-20 nm) were decorated over BT surface using a hydrothermal method. Structural and morphological characterization suggested the presence of orthorhombic BT and hexagonal SnS2 crystalline phases with high interfacial contact and strong interaction at microscopic level. Optical and photoelectrochemical (PEC) measurements revealed improved visible light absorption and enhanced charge carrier separation and migration properties. The SnS2/Bi4Ti3O12 materials displayed excellent photocatalytic activity for degradation of diazinon insecticide (> 90% with kapp ~ 0.019 min-1) in aqueous media under visible light illumination. The valence band (VB) h+ and •OH radicals were identified as major transient species responsible for photodegradation of diazinon. A Z-scheme electron transfer pathway has been proposed to explain adequately the generation of these radicals which was deduced from PEC measurements, scavenger and radical trapping experiments. Mechanistic study revealed that diazinon degradation occurred in a series of steps to produce 2-isopropyl-6-methyl-pyrimidin-4-ol as a major intermediate which was further mineralized over the photocatalyst surface. The process potential of the developed photocatalytic method has been tested for different water matrices and interfering anionic species with radical quenching activity. A series of ternary multi-heterojunction CdS/Bi20TiO32/Bi4Ti3O12 (CdSxBTC) photocatalysts were prepared by hydrothermal deposition of CdS nanoparticles (15-25 nm) over one pot combustion synthesized Bi20TiO32/Bi4Ti3O12 (BTC) nanostructures. Comprehensive characterization of the ternary composites revealed enhanced optical absorption, high interfacial contact, fast electron channelization and a prolonged excited state life time in comparison to pure components. The CdSxBTC composite materials displayed enhanced photocatalytic activity for endosulfan degradation (kapp value 6-12 times greater than pure semiconductors). The cell viability assay study disclosed non-cytotoxic nature of the treated endosulfan solution. A synergistic Type-I bridged coupled Z-scheme electron migration process accounted for robust radical generation ability (•O2− and •OH) and photocatalytic activity of the ternary composites. The facile fabrication of In2S3/Bi2Fe4O9 (ISxBFO) binary heterostructure was performed by hydrothermal deposition of In2S3 nanoparticles (20-40 nm) over combustion synthesized Bi2Fe4O9 nanocuboids. In depth characterization of the composite revealed broad spectrum UV-Vis response, large interfacial contact, facile charge carrier separation and mobility and a prolonged life time of excited state photoelectrons. The ISxBFO heterostructure material exhibited enhanced photocatalytic efficiency for aqueous phase degradation of sulfamethoxazole antibiotics (kapp=0.06 min-1) and phenyl urea herbicides (kapp= 0.028 min-1) with reaction rates 5-8 times higher than the pure components. The cell viability study confirmed non-cytotoxic nature of treated sulfamethoxazole and diuron solutions. The composite materials also showed convincing antibacterial behavior towards toxigenic Vibrio cholerae pathogen. Haemagglutination assay study revealed excellent biocompatibility of the binary composite up to a concentration of 200 mg/L. A Z-scheme electron migration mechanism accounted for the robust radical generation ability (•OH and O2–) and multidimensional photocatalytic activity of the ISxBFO heterostructure material.

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44

Hsu, Jing-Chang, and 許晉章. "The Fabrication and Characteristics Investigation of Bismuth Ferrite Thin Film by Sputtering." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/t2s496.

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碩士
國立臺灣大學
機械工程學研究所
107
In this thesis, we use radio frequency magnetron sputtering deposition technique to fabricate a multiferroic material, Bismuth ferrite(BFO), which possesses ferroelectric and anti-ferromagnetic property in the same time. We deposit BFO samples at the same temperature but anneal them at different temperature and in different atmosphere to find if there are some differences in crystal structure and electric properties. Then we choose the best of all to integrate with Barium titanate into a bilayer thin film. The combination of BTO and BFO is to learn the magneto-electric effect between ferroelectric and anti-ferromagnetic materials. In addition, we fabricate 5 different thickness ratio of the BTO/BFO bilayer to find out at which ratio will the best electric characteristic occur. According to results, the performance of Bismuth ferrite single layers is not good, the leakage current is about 10-1~10-2 ampere, the P-E loops look like a oval ball because of poor dielectric property, and worst of all, we cannot even measure the capacitance property. But everything changes in BTO/BFO bilayer structures due to the interlayer coupling effect. First, the leakage current plummets to 10-6~10-7 ampere. Second, the capacitance becomes measureable and the value is about 6x10-9 farad. Third, the maximum polarization is up to 4 μC/cm2. It’s a tremendous progress from BFO single layer to BTO/BFO bilayer. What disappoints us is that the magneto-electric measurements show that the applied magnetic field has no effect on our samples.

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45

温國宏. "Films Thickness Dependence of Ferroelectric and Photovoltaic Properties of Calcium Doped Bismuth Ferrite." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/47260632657294266642.

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碩士
國立新竹教育大學
應用科學系碩士班
103
In this experiment, the photovoltaic effect with different film thickness of 5% Ca doped BiFeO3 thin films were investigated. The probable physical mechanism were carried out many different measurements which may affect the efficiency of the photovoltaic effect. The specimen of BFO thin films and the electrode were all deposited on Si(100) by RF magnetron sputtering. First, we grew LaNiO3 on Si(100) at 450 . Second, The 5% Ca doped BiFeO3 films were deposited on LaNiO3. Third, we deposited Pt or AZO to do measurements, respectively. Film thickness was estimated by SEM and X-ray reflectivity. Film crystallinity was carried out by X-ray diffraction measurement. The morphology was measured by atomic force microscope and X-ray reflectivity. The hysteresis loop was performed by TF-2000 and the photovoltaic effect were measured by 405 nm laser. BFO was (100) highly preferred along Si (100) substrate from X-ray diffraction measurement. BFO film strain relax as film thickness increase, hence the diffraction peak position shift more close to the expected bulk value. The surface roughness, which was carried out by AFM and X-ray reflectivity has little increase as film thickness thicker. The hysteresis loop showed that the polarization slow down as the film thickness increased. The photovoltaic effect also slow down as the film thicker. The BFO built-in electric field affect the efficiency of photovoltaic effect. As the film thickness increased to 100 nm, the strain relax caused built-in electric field become weaker and the probability of electron and hole recombined increase due to distance between two electrode; therefore, the efficiency of photovoltaic hidden.

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46

Wu, chun-hsien, and 吳俊賢. "Films Thickness Dependence of Ferroelectric and Photovoltaic Properties of Lanthanum Doped Bismuth Ferrite." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/18060275025942903027.

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Анотація:

碩士
國立新竹教育大學
應用科學系碩士班
103
The photovoltaic effect was discussed under different thickness of Lanthanum doped BiFeO3 thin film. Thin film were deposited by RF-sputtering.First,LaNiO3 (LNO) was deposited on Si(100) substrate, then BiFeO3 was grown on LNO. The top electrode used aluminum doped zinc oxide (AZO). BFO thickness have 25, 50, 75, 100 and 150 nm, respectively, and the thickness was calibrated by X-ray reflectivity and field emission scanning electron microscopy. Surface roughness was carried out by atomic force microscopy. Lanthanum doped BFO have strain relaxation with film thickness increase which was observed from the peak position shift of theta-two theta scan of X-ray diffraction. As the film thickness increase, the dipole moment decrease and the built-in electric field decrease. The probability of electron-hole recombination become higher as the built-in electric field become smaller; therefore, the efficiency of photovoltaic effect become smaller. The polarization effect played an important role for efficiency of photovoltaic. As the film thickness increase, the resistance has a dramatic increase that dominate the efficiency of photovoltaic more than the polarization effect dominate. The efficiency of photovoltaic do not have straight correlation with film crystallinity, surface roughness, transmittance and leakage current by various measurements under different film thickness.

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47

Peng, Yi Ting, and 彭憶婷. "The study of photovoltaic effect and electronic structure of Neodymium doped Bismuth ferrite." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/78718378629475265465.

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碩士
國立清華大學
材料科學工程學系
104
The BiFeO3 (BFO) materials have received intensive interests in the photovoltaic effect due to the high Curie temperature and the smaller direct band gap than other ferroelectric oxide ceramics. The group of Prof. Tu Chi-Shun has shown the enhanced photovoltaic effect 56 times higher in neodymium doped BFO. Using first-principles calculations, we offered physical insights into the origins of the enhanced photovoltaic effect. The doping effect of Nd in reducing the movable charge density due to oxygen vacancies in BiFeO3 was confirmed by shifting down of Fermi level of electronic structure, resulting in more electrons or holes accumulated on the two sides of p-n junction to enhance Voc and Jsc for increasing photovoltaic effect. The Rietveld analysis showed the concentration Nd around 1.24%. Besides,the scanning transmission electron microscopy image simulation analysis of BFONd and first-principles calculations of total free energy suggested that the Nd atom replaced the Bi atom on the A site of perovskite ABO3.The electronic structure showed that the calculated direct band gaps are respectively about 2.257 and 2.227 eV for BFO and BFONd. We considered that the oxygen vacancy due to the fabrication at high temperature around 870℃, forming the sub-bandgap defect states which lowered the photovoltaic effect. The doped Nd caused the sub-bandgap defect states shifted closer to conduction band easier to overcome the trap states by thermal perturbation, and reduced the movable charge density by shifting down of Fermi level to enhance photovoltaic power conversions. In addition, the optical calculations showed that the absorption coefficient of BFONd was higher than BFO to enhance the photocurrent density, which was proportional to absorption coefficient based on Glass Law. In the quantitative analysis,we can estimated the ratio of Jsc of BFONd and BFO at the laser intensity above 800W/m2 with wavelength 405nm, which was around 30 times higher from the Voc and band gap values for same thickness of BFO and BFONd samples.

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48

Je-WeiLin and 林哲緯. "The crystalline and spin structure of doped Bismuth Ferrite --- Bulk, nanoparticle and film." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/36079884489810435055.

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博士
國立成功大學
物理學系碩博士班
100
In the dissertation, we investigate the mutiferroic bismuth ferrites Bi1−xDyxFeO3 in various forms, including bulk, nanoparticle, and thin film in order to understand the general relation between crystal structure and spin structure. In particular, the crystalline and spin structures are studied with X-ray powder diffraction (XRD), magnetization, scanning electron microscope (SEM) images, electron spin resonance (ESR), and neutron powder diffraction (NPD). The crystal structure for the bulk samples of bismuth ferrites Bi1−xDyxFeO3 with x = 0 ~ 0.05 are indexed based on the rhombohedral space group R3c in the XRD patterns. With x = 0.30 and 0.40, the structure further transforms to the orthorhombic group Pbnm. Weak magnetism of Bi1−xDyxFeO3 is studied via the electron spin resonance (ESR) of X-band (9.53 GHz) at various temperatures. The g-factor of pure BiFeO3 is 2.0, which originates from its cycloidal spin structure; while for the doped Bi1−xDyxFeO3 samples with x 〉 0.10, ESR spectra reveal a second phase with a different g-factor around 1, which is attributed to the homogeneous magnetized phase of Bi1−xDyxFeO3. Temperature dependent of ESR and neutron data further suggest a spin-reorientation at 140 and 200 K. For nanoparticles of Bi1−xDyxFeO3, it is evidential that Dy-doping can lead to suppression of grain size, and the diameter of particle d plays an important role in nanoparticles. The linearity between magnetization and 1/d indicates that the magnetic anisotropy constant Keff does not violate the magnetic anisotropy model. The data shows a great increase of magnetization M without following the linearity in M vs. 1/d at x = 0.4. There exists a critical size dc correlated with magnetic anisotropy constant and exchange constant. When dc is smaller than the cycloid spin wavelength (62 nm), the exchange constant in nanoparticle is enhanced. The ESR spectra of nanoparticles are observed and the resonance field (or g-factors) is different from that of bulk samples. In the ESR spectra of BiFeO3 thin film, there are six sharp lines observed for different resonance field (Hr). These lines are assigned to the five in-plane spin wave (SW) resonances, because the values of Hr have a linear relation with the square of spin wave index n. However, the in-plane mode of n = 5 only appears at 110 K. An unknown mode appears at temperatures of 110 K and 170 K which may be related to the spin reorientation temperatures of Fe3+ magnetic moment.

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49

Tien-YaoChiang and 蔣天堯. "Dielectric Behavior,Leakage Current and Hystereses of Polarization and Magnetization of Bismuth Ferrite/ Barium Ferrite Composite Prepared by a Novel Process." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/64033413911504354024.

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50

Allen, Marc Alexander. "Theoretical determination of electric field-magnetic field phase diagrams of the multiferroic bismuth ferrite." Thesis, 2014. http://hdl.handle.net/1828/5628.

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Bismuth ferrite (BFO) is a multiferroic material with cross-correlation between magnetic and electric orders. With no applied external fields the spin structure of BFO is anitferromagnetic and cycloidal. This ordering prevents the detection of the weak ferromagnetism known to exist in the material. The application of magnetic and electric fields of suitable strength and direction is capable of compelling the Fe3+ spins to align in a homogeneous, antiferromagnetic fashion. This report details how numerical methods were used to simulate the spin alignment of a BFO system under different fields. The results were compiled into electric field-magnetic field phase diagrams of BFO to show the divide between cycloidal and homogeneous systems.
Graduate
0607
0611
marca@uvic.ca

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