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Dixit, Manisha. "Structure-Property Correlations in Double Perovskite Systems." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1366345489.
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Adams, Ruth. "Structure-composition-property relations in B-site deficient hexagonal perovskite systems." Thesis, University of Huddersfield, 2010. http://eprints.hud.ac.uk/id/eprint/9697/.
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This thesis describes the structural and preliminary electrical characterisation of various “shifted” hexagonal B-site deficient perovskites, of generic formula, A4B3O12. These ceramics are reported to possess promising microwave dielectric properties, which are a requirement for use in the ever evolving mobile telecommunications industry. The 12R crystal structures of the Ba3-xSrxLaNb3O12 series (x = 1 – 3) were refined at variable temperatures using NPD data in space group R-3 and some interesting behaviour was exhibited. All compositions were found to be antiphase tilted, the extent of which being dependent on the A-cation size. Upon heating, the tilt angle for all members of the series was found to decrease, although no tilt transitions from R-3 to R-3m were witnessed for all phases up to 900 °C, and a change in the magnitude of permittivity at 1 MHz was observed for all members except, BaSr2LaNb3O12. Additionally evidence from preliminary low temperature data suggest relaxor ferroelectric type behaviour. Ba2SrLaNb3O12 was found to possess the most promising dielectric properties although room exists for further improvement of the quality factor (Q value). To facilitate further tuning of the dielectric properties, specifically Q, the Ba3- xSrxLaNb3-yTayO12 series (x = 0 - 3, y = 1 - 2) was investigated, with the introduction of Ta5+ on the B-site. Some interesting ordering of A- and B-sites was found to occur, and furthermore, Nb5+ was found to display a preference to inhabit the distorted environment of B(1), adjacent to the “shifted” region, compared to the undistorted B(2) site, in the perovskite block. Unusual microwave dielectric properties were displayed with all compositions exhibiting small and positive temperature coefficient of resonant frequency (TCF) values and significantly small Q values, the reverse of what is expected, thus implying that the B-site has some influence on TCF values in this case. The interesting dielectric properties may be explained by several factors, including, the increased strength associated with the covalency of the Ta-O bond compared to that of Nb-O and the presence of some significant impurity phases, particularly in the intermediate compositions that are richer in Ta5+. The LCR data collected revealed similar results as found for the Ba3-xSrxLaNb3O12 series (x = 1 – 3), highlighting the limiting nature of the temperature range which did not, in fact reflect the true response of the compositions’ behaviour. All of the compositions are antiphase tilted at room temperature therefore the collection of variable temperature diffraction data is warranted. A range of novel Ta-based intergrowth compounds were synthesised and preliminarily characterised. No detailed structural or electrical data were collected for these compounds, however, the ability to form Ta-based intergrowths, in the first instance, has been established. It is postulated that by the formation of these intergrowth phases, the dielectric properties will be effectively tuned in comparison to those of the parent oxides that they are composed of, due to the regularisation of the octahedral layers that occurs upon the formation of such intergrowth structures. This often leads to improved TCF values, and by the introduction of Ta5+, can also give improved Q values. Ta5+ was substituted for Nb5+ in the untilted 5x6y (x = 1 – 3, y = 1) layered compounds, however, it was found that to facilitate this, the replacement of Ba2+ for Sr2+ was also required on the A-site. This double substitution was a requirement to obtain compositions closer to single phase Ta-rich phases compared to Nb-rich compositions.
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Pack, Maria Joyce. "Complex metal oxide materials : synthesis, structural characterisation and development of combined EXAFS and powder differaction analysis." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243098.
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Bing, Yonghong. "Synthesis, structure and properties of high piezo-and ferroelectric complex perovskite systems /." Burnaby B.C. : Simon Fraser University, 2005. http://ir.lib.sfu.ca/handle/1892/2032.
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Al-Hamadany, Raied Abass Saleh. "Quantum mechanical study of point and molecular defects in perovskite nano-systems." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2620.
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Strontium titanate is a perovskite dielectric material with a wide band-gap of 3.25 eV and a large relative dielectric permittivity of 300 at room temperature. The combi- nation of these properties makes SrTiO₃ a promising candidate for various industrial applications. However, there is growing evidence that oxygen vacancies have a sig- nificant impact upon its use, with the diffusion and deep donor level of the oxygen vacancy leading to electrical leakage. A qualitative understanding of the diffusion and electrical properties of oxygen vacancies can help to provide a clearer picture of many phenomena such as resistive switching and leakage current. Utilising SrTiO₃ thin films in various devices leads it to be in contact with other substances such as metal electrodes or other oxides. The lattice-mismatch between thin film SrTiO₃ and other material means that thin film SrTiO₃ is grown under bi-axial strain. The magnitude and the value of strain are driven by the lattice parameters of the material it is in contact with and the strain might be compressive or tensile. Here, the results of first principle density functional theory calculations performed using the AIMPRO code are presented. It is found that thin film SrTiO₃undergoes a transition from cubic to tetragonal structure with polarisation along the [001] and [110] directions under compressive and tensile (001) strain respectively. As a key parameter for tailoring the properties of SrTiO₃, the diffusivity of oxygen vacancies under bi-axial tensile or com- pressive strain has been investigated. The structural transition yields anisotropy in oxygen vacancy diffusion for diffusion within and between planes parallel to the plane of strain. Under (001) compressive strain it is found that, in the range of strains consistent with common substrate materials, diffusion energies in different directions are significantly affected, and for high values of strain may be altered by as much as a factor of two. The resulting diffusion anisotropy is expected to impact upon the rate at which oxygen vacancies are injected into the film under bias. By contrast, under (001) tensile strain, the diffusion of oxygen vacancies is predicted to increase in all directions (in-plane and inter-plane), albeit more so in the direction perpendicular to the plane of strain. Doping with a foreign element, namely a transition metal, is an alternative proce- dure for controlling the properties of SrTiO₃. The structural, thermodynamic, electri- cal and electronic properties of zinc-doped SrTiO₃ have been studied in the framework of density functional theory. The interaction of Zn with oxygen vacancies, which is a central theme in this thesis, has also been considered. In oxygen-lean conditions, however, the formation of oxygen vacancies is strongly favoured. It is found that VO may be bound to ZnTi with a binding energy of around 0.81±0.08 eV and no states in the gap. The role that ZnTi may have in the compensation for or capture of oxy- gen vacancy effects is discussed, along with the thermodynamics of Zn under various growth conditions.
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MATTIELLO, SARA. "VARIATIONS ON SELF-ASSEMBLY OF SURFACTANT-BASED CONFINED SYSTEMS." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/199111.
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Il filo conduttore del lavoro è il self-assembly di surfattanti per varie applicazioni nel campo delle nanotecnologie. I surfattanti sono molecole composte da una testa polare e una coda apolare che, in acqua, formano aggregati nanometrici detti micelle. L’interno di una micella è formato dalla porzione apolare dei surfattanti, che minimizza così la sua interazione con l'acqua, per cui non ha affinità. Dal momento che è composto da catene organiche, l'interno delle micelle forma un ambiente adatto alla solubilizzazione di altre specie organiche in base al principio "il simile scioglie il simile". Le micelle funzionano quindi come una “fase segregata” in cui è possibile far interagire tra loro specie poco solubili in acqua.
Nei corso del primo progetto, abbiamo scoperto che un noto surfattante industriale, il Kolliphor® EL, forma micelle fortemente insensibili alla presenza di ossigeno. Questo ci ha permesso di utilizzarle come “scatole fotoniche” per il processo fotofisico di Triplet-Triplet Annihilation Up-Conversion, che sfrutta i livelli di tripletto di due specie organiche interagenti per convertire fotoni di bassa energia in fotoni di energia più elevata. Dal momento che l'ossigeno è un noto quencher di tripletti, è necessario un ambiente anossico. Abbiamo ottimizzato la resa quantica del processo in micella, e utilizzato con successo le micelle per imaging cellulare.
Lo stesso surfattante è stato poi implementato per lo svolgimento di reazioni di sintesi organica di tipo Suzuki-Miyaura, anch’esse fortemente sensibili alla presenza di ossigeno, in condizioni di atmosfera non controllata. Abbiamo dimostrato che il Kolliphor può essere utilizzato con successo per la sintesi senza necessità di deossigenare l’ambiente di reazione, permettendo di ottenere rese di reazione comparabili a quelle di designer surfactants specifici per reazioni di coupling. Inoltre, abbiamo verificato che questo tensioattivo è utilizzabile come “nanoreattore” per la preparazione specificamente di semiconduttori organici.
Le micelle sono oggetti dinamici, che continuamente si formano e digregano della fase acquosa. Nel corso del terzo progetto, abbiamo studiato la possibilità di stabilizzarle utilizzando un metodo originale, ispirato ai network polimerici interpenetrati. L’idea era di creare un sistema che, anche se formato da specie non legate chimicamente, fosse difficilmente separabile poiché formato da catene "aggrovigliate". All'atto pratico, abbiamo sintetizzato un co-surfattante polimerizzabile, e lo abbiamo disperso in una fase micellare formata da un surfattante ramificato: la polimerizzazione, avvenendo dopo la dispersione, avrebbe permesso di creare una catena polimerica interamente tra le maglie del tensioattivo. Dopo aver ottimizzato la polimerizzazione, abbiamo verificato non solo l’incrementata stabilità del sistema alla diluizione e alla temperatura, sintomatica della formazione di un sistema del tipo ricercato, ma anche che il nuovo materiale ha un’incrementata capacità di ritenzione del carico.
Infine, surfattanti cationici (nello specifico, sali di ammonio) sono stati utilizzati per la sintesi di perovskiti colloidali attraverso un semplice processo di precipitazione da non-solvente. Nel caso di uso di sali di alchilammonio, le “piastrelle” ottenute mantengono le proprietà delle perovskiti cresciute come cristalli singoli, benché la sintesi sia sotto controllo cinetico anziché termodinamico. Inoltre, è possibile riconfigurarle in soluzione, variandone composizione e morfologia, tramite reazioni di scambio di alogeni in opportune condizioni. Quando il legante usato è invece il sale di ammonio di un poli(dimetilsilossano), la perovskite cresce in forma di singoli strati cristallini, sottilissimi e molto ampi. Le proprietà meccaniche di questo materiale rimangono molto simili a quelle del polimero di partenza, facendolo quindi assomigliare a un “semiconduttore liquido”.Self-assembly of surfactant-based structures, and their application in the nanotechnology field, is the fil rouge connecting all the projects discussed. Surfactants are molecules formed by a polar head and an apolar tail covalently connected. In water, they form nanometric aggregates called micelles. The inner portion of a micelle is formed by the apolar blocks of the surfactants, which in this way minimize the interaction with the surrounding aqueous environment. As the inner core is formed by organic chains, it is apt to solubilize other organic species (on the basis of “like dissolves like” principle). Micelles therefore work as a segregated phase, which makes possible the interaction between poorly water-soluble species. During early stages of reaserch, we found that Kolliphor® EL, a widespread and cheap industrial surfactant, forms micelles strongly insensitive to oxygen. We therefore used them to carry out oxygen sensitive processes. A first project focused on their use as “photonic boxes” for Triple-Triplet Annihilation Up-Conversion (TTA-UC). Photophysics of this process is based on triplet levels of organic molecules, easily quenched by molecular oxygen. We developed an easy protocol to perform TTA-UC in air, optimized quantic yield of the process and proved that the obtained micellar dispersion is suitable for cellular imaging. We subsequently used Kolliphor micelles as “nanoreactors” to perform organic synthesis the like Suzuki-Miyaura coupling. This reaction makes use of oxygen sensitive palladium catalysts. We demonstrated that Kolliphor can be successfully used to perform this kind of reaction in standard oxygenated atmosphere, and the reaction yields are comparable to those obtained with surfactants specifically designed for coupling reactions. We also challenged Kolliphor in the synthesis of organic semiconductors with very good results, although the developed method needs some refinements. Micelles are dynamic objects, continuously forming and disrupting in the aqueous phase, a feature that might be discouraging for a series of applications. We developed an original method, inspired by interpenetrated polymer network properties, to stabilize micellar systems. The idea was to create a hardly disentanglable system as the result of mechanical hindrance instead of bond formation, which is the most used strategy. We therefore designed a polymerogenic co-surfactant to be dispersed within a micellar solution formed by a branched surfactant. We aimed at polymerizing the co-surfactant after dispersion in order to create a polymeric chain entangled within the branched surfactant polar heads. We optimized the polymerization reaction in order to obtain a full conversion of the monomers, and therefore we proved the system to be more stable to both dilution and temperature increasing. The newly obtained material, moreover, can be still loaded with organic species, and it shows an increased retention of loading upon solvent evaporation. Finally, we used two different families of cationic surfactant (specifically, ammonium salts) to synthesize colloidal hybrid perovskites through a simple non-solvent precipitation technique. The first family of surfactants is represented by classic alkylammonium halides: they allow to synthesize perovskite nanoplatelets which maintain the properties of the material prepared as single crystal. Moreover, they can be reconfigured in solution: halogen exchange reactions under tailored conditions, in fact, allow to modify both their composition and morphology. The second surfactant used is the ammonium salt of poly(dimethylsiloxane): use of this polymer allows to grow a naturally two-dimensional, unit-cell thick material. Mechanical properties of these perovskites resemble those of the starting polymer, meaning that these platelets might behave like something similar to a “liquid semiconductor”.
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Currie, David Blake. "A study of cation replacement in perovskite-related systems including high temperature superconductors." Thesis, University of the West of Scotland, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254391.
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Chu, Zili. "Neutron diffraction studies of disorder in R₂T₁₇ (R=Nd, Dy, Sm, Tb and T=Fe, Si, Al) and RFeO₃ perovskite systems /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074388.
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Vernon, Marwyn. "Evaluating the economic viability of Perovskite – SHJ monolithically integrated photovoltaic modules." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-357948.
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In this study, the financial and economic viable of perovskite-SHJ tandem solar cells were determined using a detailed bottom-up cost model and energy-yield calculations. Attention to specific advancements in perovskite solar cell layer technology and large-scale deposition have been taken into account to create a realistic, viable commercial scale option for tandem production. A reference tandem technology is used to determine the overall manufacturing cost and minimum sustainable price. Models used show that the tandem technology has the potential to be cost competitive with existing silicon technology given the uncertainty and sensitivity of the values used in this study. It was examined further how non-STC energy yield and service life contributes to the overall economic viability of the tandem module within residential, commercial and utility scale of application. Given the reference tandem module, it is expected to be competitive at the residential level with existing silicon technology if perovskite layers' service life is greater than 20 years. In commercial and utility application, the tandem model is not economically viable due to the reductions seen in the area- and project-related installation costs for existing technology. This thesis concludes by presenting the current limitations in perovskite technology that would inhibit adaptation of this into commercial-scale production and presents alternative applications in which tandem modules would be more favourable.
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Nguyen, Lisa. "Investigation of Selected Molecular and Crystalline Systems using Ultrafast Time Resolved Infrared Spectroscopy." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1574629448290612.
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Wang, Dashan 1948. "Thermal stability of SrFeO3SiO2Si and SrFeO3AI2O3 thin film systems : transmission electron microscopy study of interfacial structures of the thin film systems and conductometric sensing response of SrFeO3AI2O3." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115907.
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The literature review indicates that studies on the structures and properties of perovskites materials have shown attractive applications in the fields of energy, catalysts and sensing materials for fuel cell and sensing industries. Kinetic phenomena in thin film systems, such as solid state amorphization and interface reactions due to diffusion during thin film deposition, are introduced indicating that thermal stability is a concern in thin film sensor device application. The principle of traditional methods of materials characterization is briefly discussed. Emphasis is placed on the functions of analytical transmission electron microscopy.The SrFeO3/SiO2/Si and SrFeO3/Al 2O3 thin film systems have been studied using transmission electron microscopy. The thin films of SrFeO3 were grown by pulsed laser deposition. For the SrFeO3/SiO2/Si system, TEM characterization showed that the microstructure of the film deposited at room temperature contained crystalline and amorphous layers. Silicon diffusion into SrFeO3 films occurred at the SiO2 interface. The silicon-induced interfacial reactions resulted in phase transformations and the growth of complex crystalline and amorphous phases. The principal compositions of these phases were Sr(Fe,Si)12O19, SrOx and amorphous [Sr-Fe-Si-O].
The films in the SrFeO3/Al2O3 system were deposited onto single crystal and sintered polycrystalline Al2O 3 substrates at room temperature and 700°C and subjected to annealing for various periods of time at 700-1000°C. TEM characterization showed that the morphology of the film varied with changes in deposition temperature: a columnar structure was produced at room temperature and layers containing crystalline grains were produced at 700°C. The interfacial structures of the films remained unchanged below 700°C. Interfacial reactions were observed following annealing at 850°C for 5 hours. The phase transformation at the interface was characterized for the film annealed at 1000°C for 5 hours, for which the principal phases were identified as SrAl2-xFe xO4 and SrFe12-yAlyO19. As a result, an isothermal section at 1000°C of a ternary phase diagram for SrO-Al2O3-Fe2O3 is proposed. Evaluation for thin film conductometric sensing applications indicated that the untreated films deposited at 700°C onto both single crystal and sintered Al2O3 substrates exhibited a similar temperature dependency of conductivity in air and a p-type gas sensor response to oxygen and propane at 500°C.
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Wilson, Jamie Robyn. "Measurement and prediction of nonlinear harmonics as a tool for dynamic characterization of electrochemical systems /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9852.
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Grill, Irene [Verfasser], and Achim [Akademischer Betreuer] Hartschuh. "Opto-electronic characterization of charge transport in hybrid perovskite thin film systems for photovoltaic applications / Irene Grill ; Betreuer: Achim Hartschuh." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2018. http://d-nb.info/115849615X/34.
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Pellegrino, Anna Lucia. "Synthesis of hybrid metalorganic/inorganic systems and doped halide thin films for photovoltaics." Doctoral thesis, Università di Catania, 2019. http://hdl.handle.net/10761/4141.
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The aim of the present PhD thesis has been the synthesis of novel materials for photovoltaic (PV) technologies. One possible way to increase the conversion efficiency of silicon solar cells is to shift the incident sunlight spectrum, converting photons poorly exploited by the active PV material into more effective photons. The materials studied as energy converters, consist of thin film layers integrated in the PV panel and made of a host material and an active luminescent species. In the present thesis, the energy conversion systems made of lanthanide doped fluorides (CaF2, NaYF4, NaGdF4, KYF4 and YOF) have been synthetized using MOCVD and sol-gel methods and deeply studied for their potential integration in silicon solar cells. Together with the traditional silicon PV technology, a new class of PV materials, based on inorganic multi-junction technology, new hybrid materials and organic dye-sensitized solar cells (DSSC) is subject of interest in the last years. Hybrid metalorganic/inorganic systems of Eu-complex/NiO films have been developed for the DSSC technology and for the potential improvement of the PV material with new functionalities, that combine the semiconductor behavior of the inorganic part to the luminescent properties of the metalorganic component. The all-inorganic halide perovskite CsPbBr3 has been synthetized through a precipitation method. The perovskite CsPbBr3 has a semiconductor behavior, with an energy band gap useful in the PV application and has the advantages to not have any labile or expensive organic components.
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Melo, Luna Carlos Andres [Verfasser], and John Henry [Akademischer Betreuer] Reina. "Quantum coherence and correlations in photonic qubits and photoactive hybrid organometallic Perovskite systems / Carlos Andres Melo Luna ; Betreuer: John Henry Reina." Bayreuth : Universität Bayreuth, 2019. http://d-nb.info/1188314025/34.
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Cimaroli, Alexander J. "Development of Deposition and Characterization Systems for Thin Film Solar Cells." University of Toledo / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1481295690696407.
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Papadopoulos, Konstantinos. "Investigation of magnetic order in nickel-5d transition metal systems." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-383009.
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Double perovskite materials exhibit alterations in magnetic order through manipulation oftheir crystal structure. Certain ultra thin metallic bilayers can create an exotic magnetic stateof confined spin textures called skyrmions. In both cases, new atomic arrangements leadto new electrical and magnetic properties. The following work comprises two studies, bothof which examine the magnetic properties of transition metals in either powder or thin filmsamples. The first part is dedicated to a series of muon spin rotation and relaxation (muSR)experiments on a LaSrNiReO6, double perovskite, powder sample. In the muSR technique, aspin polarized muon beam is focused onto a powder envelope in low pressure and temperatureconditions. The spins of the implanted muons evolve depending on the intrinsic or externallyapplied magnetic field according to Larmor precession. The measurement is based onthe detection of decay positrons that carry this precession information on their preferreddecay directions. Measurements that were realized in wTF, ZF and LF setups, reveal asecond transition to magnetic order at Tc ≃ 22K, below a transition that was observed at T =261K from magnetic susceptibility measurements. The experimental results point to threemagnetic phases, paramagnetic for T > 261K, dilute ferrimagnetic for 22 < T < 261K and amagnetically ordered state for T < 22K, that may implicate ferro- and antiferromagnetismfrom Ni sublattices and Ni-Re interactions. The second part follows an attempt to produce and characterize ultra thin bilayer filmsfor the observation of interfacial chiral structures and skyrmions. Co/Fe/MgO (100) andW/Ni/Cu (100) bilayers were grown with magnetron sputter deposition in various layerthicknesses and their structure was determined by X-ray reflectometry (XRR). The XRRscans presented a relatively thick-layered Co/Fe/MgO film, while extremely thin and roughW/Ni/Cu bilayers, for the purposes of studying films with broken interfacial inversionsymmetry. This study was concluded with indicative magneto-transport measurements thatalso point to the reconfiguration of the growth procedure.
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Erten, Onur. "Electronic and Magnetic Properties of Double Perovskites and Oxide Interfaces." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376496346.
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Francese, Tommaso <1988>. "First-Principles Investigation of a Doped BaTiO3-based Perovskite System." Master's Degree Thesis, Università Ca' Foscari Venezia, 2022. http://hdl.handle.net/10579/21469.
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The intriguing nature of the BaTiO3 perovskite system has been largely debated and investigated in recent years thanks to its intrinsic properties like high visible-light absorption coefficients, high photoluminescence quantum yield, long charge carrier diffusion length, colossal magnetoresistance, superconductivity, and many other interesting and valuable solid-state properties. The general application of the perovskite systems covers a wide range of technological devices and solutions that are foreseen to be part of the next future general technological advancement. In this perspective, our work focuses on the ab initio prediction of the basic properties of a subset of BaTiO3-based perovskite models which display different doping rates ranging from 25 to 50%. These doping are performed by replacing Titanium (Ti) with Tin (Sn) (50% substitution) and Barium (Ba) with Strontium (Sr) (25 and 50% substitution), paving the way for more complex modifications required to engineer the intrinsic properties of the studied systems, such as band structure, density of states, bulk modules etc.
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Ismailova, Leyla [Verfasser], and Leonid [Akademischer Betreuer] Dubrovinsky. "An experimental study of the system FeO-Fe2O3-SiO2 at high pressures and temperatures : Garnet, perovskite and post-perovskite phases / Leyla Ismailova ; Betreuer: Leonid Dubrovinsky." Bayreuth : Universität Bayreuth, 2016. http://d-nb.info/1120491541/34.
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NASCIMENTO, Mylena Pinto. "Estudos das propriedades estruturais e morfológicas, e avaliação da possibilidade de utilização como sensores de gases das PEROVSKITAS TRFeO3 (TR= Sm, Eu, Gd)." Universidade Federal de Pernambuco, 2010. https://repositorio.ufpe.br/handle/123456789/18286.
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Esse trabalho apresenta a produção e caracterização estrutural e morfológica das perovskitas simples TRFeO3 (TR = Sm, Eu, Gd), e o estudo da possibilidade de utilização desses sistemas como sensores de gás. Todas as amostras de TRFeO3 foram produzidas pela síntese de reação no estado sólido, que é uma síntese ainda pouco explorada na literatura para a obtenção desse sistema. O estudo das propriedades estruturais foram realizados por difração de raios X e adsorção e dessorção de N2, e a análise morfológica foi realizada através da microscopia eletrônica de varredura (MEV). Todas essas análises foram estudadas em função da temperatura e tempo de sinterização, bem como do cátion da terra rara utilizada. Através das análises por difratometria, foi possível a identificação da fase formada e a estimativa do tamanho médio do cristalito. Tais análises revelaram coexistência de fase com o composto TR3Fe5O12 para amostras sinterizadas a 1200°C, independente do tempo de sinterização utilizado, onde houve uma tendência a um equilíbrio na formação das fases. Já as amostras sinterizadas a 1100°C apresentaram-se monofásicas com o composto TRFeO3, com tamanho de cristalito variando conforme o tempo de sinterização. As imagens de MEV mostraram uma morfologia porosa, adequada para sensores de gás, apresentando grãos com formatos arredondados e formação de pescoço, conforme o tempo de sinterização utilizado. Independente da temperatura e tempo de sinterização, o tamanho dos grãos variaram em torno de 1 mm. Para avaliar a sensibilidade aos vapores de gasolina, foi desenvolvido um sistema baseado em medidas de resistividade elétrica, usando o método de 4-fios de Kelvin. Os resultados revelaram que um mecanismo diferente da literatura, onde a resistividade do material diminuiu quando exposto à atmosfera da mistura ar sintético/gasolina, a partir da temperatura ambiente, com boa reprodutibilidade. Através da dinâmica de tempo de resposta, em alta concentração de vapor do combustível utilizado, foi verificado que a capacidade sensorial dos compostos estudados, possivelmente, possui uma limitação com relação aos parâmetros estruturais, já que ambas propriedades estão relacionadas. Essa observação foi comprovada através do estudo realizado pelas medidas de adsorção e dessorção de N2, onde a área superficial das amostras foi em torno de 1,8 m2/g, o que diminui, significantemente, a sensibilidade.
This paper presents the production and structural and morphological characterization of simple perovskites REFeO3 (RE = Sm, Eu, Gd), and the possibility of using such systems as gas sensors. All REFeO3 samples were produced by the synthesis of solid state reaction, which is still little explored in the literature to obtain this system. The study of structural properties were carried out by X-ray diffraction and N2 adsorption and desorption, and the morphological analysis by scanning electron microscopy (SEM). All these tests were studied as a function of temperature and sintering time, and the rare earth cation used. Through this analysis by diffraction was possible to identify the phase formed and the estimated average size of crystallite. Such analysis revealed the coexistence of phase with the compound RE3Fe5O12 for samples sintered at 1200°C, regardless of time of sintering, where there was a tendency to an equilibrium in the formation stage. The samples sintered at 1100°C were presented with the monophasic compound REFeO3, with crystallite size varying according to the sintering time. The SEM images showed a porous morphology, suitable for gas sensors, showing grains with rounded shapes and neck formation, in accordance with the sintering time used. The grain size varied around 1 mm independent of temperature and sintering time. A system based on measurements of electrical resistivity, using the method of 4-wire Kelvin, was developed to detect the sensitivity to the vapors of gasoline. The results revealed that a different mechanism from literature, where the resistivity of the material decreased when exposed to atmospheric mixing synthetic air/gasoline from the ambient temperature, with good reproducibility. Through the dynamic response time, at high concentration of gasoline vapor, it was found that the sensory ability of the compounds studied, possibly, has a limitation with respect to structural parameters, since both properties are related. This observation was confirmed by the study performed by the measures of the adsorption and desorption of N2, where the surface area of the samples was about 1.8 m2/g, which decreases significantly the sensitivity.
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Shafeie, Samrand. "Structure and Properties Investigations of the La2Co1+z(Ti1-xMgx)1-zO6 Perovskite System." Licentiate thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-55418.
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Perovskite based materials have great potentials for various energy applications and the search for new materials for uses in SOFCs has largely been concentrated to this class of compounds. In this search, we have studied perovskite phases in the system La2Co1+z(Ti1-xMgx)1-zO6, with 0 x 0.9 and z = 0.0, 0.2, 0.4, 0.6. Crystal structures were characterized by XRD and, for selected compositions, also by NPD and SAED. They exhibit with increasing x, as well as increasing z, a progressive increase in symmetry from monoclinic to orthorhombic to rhombohedral. The main focus in this work has been on the investigation of structure-property relations for compositions with 0.0 x 0.5 and z = 0. The nominal oxidation state of Co increases for these with increasing x, from Co2+ for x = 0 to Co3+ for x = 0.5. Magnetic measurements and XANES studies showed that the average spin state of Co changes linearly with increasing x, up to x = 0.5, in accordance with varying proportions of Co with two fixed oxidation states, i.e. Co2+ and Co3+. The data suggests that the Co3+ ions have an IS spin state or a mixture of LS and HS spin states for all compositions with nominally only Co2+ and Co3+ ions, possibly with the exception of the composition with x = 0.1, 0.2 and z = 0, for which the data indicate that the spin state might be HS. The XANES data indicate furthermore that for the perovskite phases with z = 0 and x > 0.5, which in the absence of O atom vacancies contain formally Co4+, the highest oxidation state of Co is Co3+, implying that the substitution of Ti4+ by Mg2+ for x ³ 0.5 effects an oxidation of O2- ions rather than an oxidation of Co3+ ions. The thermal expansion was found to increase nearly linearly with increasing oxidation state of Co. This agrees well with findings in previous studies and is attributable to an increase in the ionic radius of Co3+ ions with increasing temperature, due to a thermal excitation from a LS to IS or LS/HS spin states. High temperature electronic conductivity measurements indicate that the electronic conductivity increases with an increase of both relative and absolute amount of Co3+. The latter can be attributed to an increase in the number of Co-O-Co connections. Additional high temperature magnetic measurements for selected samples, whose susceptibilities did not follow a Curie law behaviour up to room temperature, showed effective magnetic moments that did approach plateaus even at high temperatures (900 K). Interpretations of these data are, however, hindered by the samples losing oxygen during the applied heating-cooling cycle. The present study has shown that the investigated system is suitable for further studies, of more fundamental character, which could provide further insight of the structure-property relationships that depend on the oxidation state of Co.Studies of cobalt based perovskites for cathode materials in solid oxide fuel cells.
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Nye, Daniel. "Investigation of the structure of the perovskite system (1-x)BiFeO3-(x) (K0.5Bi0.5)TiO3." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/93412/.
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The (1-x)BiFeO3-(x) (K0.5Bi0.5)TiO3 (BFO-KBT) system has been investigated with respect to composition and temperature. Powder samples have been synthesised by the traditional solid state method at regular intervals across the compositional range. High resolution powder x-ray diffraction measurements have been made on these powders between room temperature and up to 950ºC. The data from these measurements have been analysed by the Rietveld method, and the results of these refinements have been used to construct a phase diagram of the BFO-KBT system. It was found that there are no sharp transitions in the phase diagram, either with composition or with respect to temperature, and that aside from the BFO end member, all samples investigated were best fitted with a mixed phase model. At low mol% KBT, it was found that the mixed phase model that best described the system was a mix of rhombohedral R3c and cubic Pm3m. As the mol% KBT was increased, the cubic phase increased, becoming dominant between 15% KBT and 20% KBT. The rhombohedral phase diminished with increasing mol% KBT and was no longer a component in the mixed phase system beyond 60% KBT. At 70% KBT, the room temperature system could still not be modelled with a single phase. A mix of cubic Pm3m and monoclinic P1m1 was used to model the system. At 90% KBT, the model was again found to be best fitted by a different mix of phases, specifically a mix of monoclinic P1m1 and tetragonal P4mm phases were used to model the data. The tetragonal phase was found to become more dominant from this point with increasing mol% KBT, but even the KBT end member was found to be best modelled with a mix of monoclinic P1m1 and tetragonal P4mm phases. It was found that all samples become more cubic with increasing temperature. It was found that the temperature at which the change to a cubic state occurred decreased with increasing mol% KBT. It was also found that at high mol% KBT and high temperature, there was phase separation into a two-cubic mixed phase model instead of the expected single Pm3m cubic phase. This phase separation has been linked to the reported morphotropic phase boundary in the material. The BFO-KBT system was found to change little with respect to temperature below 500ºC, which makes it an attractive material for high temperature device applications if doped with a material with a stronger piezoelectric response. In addition, single crystal x-ray diffraction of BFO-KBT crystals has been undertaken with laboratory-based and synchrotron systems. It was found that the latter was necessary to obtain good results from a refinement of the data in SHELXL due to the absorption of the BFO-KBT system, minimised through the use of a much higher energy x-ray beam. It was found in JANA2006 that the BFO-KBT system was best fit with anharmonic atomic displacement parameters, which was linked to the difference between the short range and long range order in the material.
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Ali, Fawad. "Investigation of metal oxides thin films developed by PVD system for perovskite solar cells." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/127139/1/Fawad_Ali_Thesis.pdf.
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This research presents thin film deposition and characterization of metal oxides using industrially viable Physical Vapour Deposition (PVD) techniques. The research examines low temperature processed electron and hole transport metal oxides for high performance and stable perovskite solar cells. The physical, chemical, optical and electronic properties of the films were investigated and their device performance has been evaluated. The performance of the device improved and the materials cost reduced by replacing the expansive organic materials with more stable inorganic metal oxides.
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Sharp, Matthew David. "The Ba-Pb-O system and its potential as a solid oxide fuel cell (SOFC) cathode material /." St Andrews, 2007. http://hdl.handle.net/10023/378.
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Langhammer, Christoph. "Kalorimetrische Untersuchungen zu Magnetismus, Supraleitung und Nicht-Fermi-Flüssigkeits-Effekten in Systemen mit starken Elektronenkorrelationen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2000. http://nbn-resolving.de/urn:nbn:de:swb:14-991032056140-31582.
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Die Arbeit befaßt sich mit der Messung und Analyse der spezifischen Wärme verschiedener stark korrelierter Elektronensysteme bei tiefen Temperaturen und hohen Magnetfeldern. Zunächst wird der im Rahmen dieser Arbeit verwendete, auf der Meßmethode der thermischen Relaxation beruhende Aufbau des Kalorimeters (Einsatzbereich 0.05K<T<4K und 0<B<12T) ausführlich erläutert. Danach werden die Ergebnisse von Messungen an den drei Schwere-Fermionen-Verbindungen CeCu2Si2, CeNi2Ge2 und YbRh2Si2 dargelegt. Wenngleich alle drei Systeme bei tiefen Temperaturen durch den für Schwere-Fermionen-Systeme charakteristischen, stark erhöhten elektronischen Beitrag zur spezifischen Wärme gekennzeichnet sind zeigen sich deutliche Unterschiede im beobachteten Grundzustandsverhalten. An CeCu2Si2 wird die für T<1K auftretende Konkurrenz zwischen einem supraleitenden und einem magnetischen Grundzustand ausführlich studiert. In YbRh2Si2 zeigt sich bei einer für 4f-Systeme bemerkenswert tiefen Temperatur von ca. 70mK ein Übergang in eine magnetische Phase, während der Grundzustand von CeNi2Ge2 wegen stark ausgeprägter Probenabhängigkeiten immer noch kontrovers diskutiert wird. Des weiteren zeigen alle drei Verbindungen deutliche Abweichungen vom Verhalten einer Fermi-Flüssigkeit. Die Theorie der Fermi-Flüssigkeit hat sich für metallische Verbindungen als sehr erfolgreich auch bei der Beschreibung des Verhaltens eines Systems aus stark wechselwirkenden Ladungsträgern erwiesen. Warum diese Theorie auf die untersuchten Verbindungen nicht anwendbar zu sein scheint, wird im Rahmen moderner Modellvorstellungen wie z. B. der Nähe zu einem quantenkritischen Punkt diskutiert. Die an Sr2RuO4, dem ersten Kupfer-freien Perowskit Supraleiter, durchgeführten Messungen der spezifischen Wärme dokumentieren das Auftreten von zwei Zusatzbeiträgen für T<Tc, die eine Interpretation der spezifischen Wärme des supraleitenden Zustands von Sr2RuO4 im Hinblick auf die Topologie des Ordnungsparameters deutlich erschweren.
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Goldner, Philippe. "Processus de paires dans une perovskite hexagonale : luminescence anti-stokes dans les systemes erbium-erbium et erbium-ytterbium." Paris 6, 1993. http://www.theses.fr/1993PA066376.
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L'etude spectroscopique de differents processus de conversion de frequence est presentee dans cscdbr#3. Dope ou codope par l'erbium et l'ytterbium. Les impuretes trivalentes forment dans cette matrice des paires compensees en charge de facon quasi-exclusive. Une etude par spectroscopie a haute resolution et a basse temperature, de structures de paires a mis en evidence, outre les dimeres symetriques (lacune centrale), un complexe asymetrique (lacune laterale). Dans ce cas, les ions sont couples par un fort transfert d'energie. Dans les echantillons codopes, des paires mixtes ont ete identifiees. D'autre part, un fort couplage entre ions d'une meme paire a ete observe lors de l'etude de la conversion visible-ultraviolette. La position en energie et la duree de vie de niveaux de l'erbium situes a haute energie ont ete mesurees par absorption dans l'etat excite. A partir de ces resultats, l'ensemble des processus donnant naissance aux emissions anti-stokes ont ete analyses a travers la dynamique de fluorescence, ce qui a revele l'importance des mecanismes de competition entre relaxations croisees. Enfin la formation de paires mixtes s'est revelee defavorable au rendement de conversion infrarouge-visible
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Bouilly, Guillaume Jacques. "Synthesis and characterization of transition metal oxides and oxyhydrides using epitaxial thin films deposition." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/200450.
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BIOTTEAU, GAEL. "Etude par diffusion elastique et inelastique de neutrons de systemes perovskites dopes au calcium la 1 - xca xmno 3 presentant des proprietes de magnetoresistance geante." Paris 7, 2000. http://www.theses.fr/2000PA077240.
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Ce travail a ete consacre a l'etude experimentale des proprietes magnetiques statiques et dynamiques des composes la 1 xca xmno 3 faiblement dopes dans la phase isolante. L'etude de la structure magnetique nous a permis de construire jusqu'au dopage x = 0. 2 le diagramme de phase constitue de plusieurs phases magnetiques en fonction de la concentration et de la temperature, dont deux principales : une phase antiferromagnetique cantee en moyenne, pour 0 < x < 0. 125, et une phase ferromagnetique isolante pour 0. 125 x 0. 2. La nature de cet etat cante nous a partiellement ete revelee par des experiences de diffusion diffuse. En effet, ces mesures ont permis l'observation directe d'inhomogeneites ferromagnetiques statiques de petites tailles dans une matrice antiferromagnetique cantee. Ces polarons magnetiques ont une forme et une repartition anisotropes, refletant la structure antiferromagnetique de type a. L'evolution de leur taille caracteristique est faible avec la concentration et s'effectue principalement dans les plans (a,b) ferromagnetiques, l'antiferromagnetisme empechant leur developpement dans la direction c. L'etude de la dynamique de spin a permis de mettre en evidence la coexistence de deux excitations magnetiques, l'une attribuee au couplage de super echange et l'autre, mesuree a plus basse energie, au couplage de double echange induit par les inhomogeneites ferromagnetiques riches en trous. Lorsque l'ordre antiferromagnetique disparait a x = 0. 125, les regions riches en trous s'etendent a grande echelle, le seuil de coalescence etant depasse, et une seule branche d'onde de spin est observee presentant deux regimes en q, separes a la valeur q 0, par un brusque saut de l'energie. Le regime des petits q est attribue aux couplages de double echange a grande echelle dans les regions riches en trous qui ont percole et le regime des grands q aux couplages locaux de super echange entre les ions mn 3 +.
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Liu, Shuhao. "Electronic Transport in Functional Materials and Two-Dimensional Hole System." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1522893320666086.
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DIOT, NADEGE. "Nouveaux oxynitrures de type perovskite ou fluorine dans les systemes m-ta(nb)-o-n (m : alcalinoterreux) et ln-w-o-n (ln : element de terre rare) en vue d'une application comme pigments colores." Rennes 1, 1999. http://www.theses.fr/1999REN10107.
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La recherche de nouveaux pigments colores dans le domaine des composes de type nitrure a conduit a la synthese et la caracterisation de nouveaux oxynitrures dans les systemes m-ta(nb)-o-n (m : alcalinoterreux) et ln-w-o-n (ln : element de terre rare). De nouveaux oxydes de type perovskite ont ete decouverts dans le systeme sr-ta-o. Ils forment un domaine de solution solide entre les compositions sr(sr 0. 3 7ta 0. 6 3)o 2. 9 5@ 0. 0 5 et sr(sr 0. 5ta 0. 5)o 2. 7 5@ 0. 2 5. Les oxynitrures correspondants sont isotypes des oxydes precurseurs et presentent une gamme de couleurs s'etendant du jaune pale a l'orange lorsque l'enrichissement en azote croit. L'influence de la nature de l'alcalinoterreux ou du metal de transition sur la couleur a ete determinee grace a l'etude des systemes ca(sr,ba)-ta(nb)-o-n ; un nouvel oxynitrure sr 2nbo 3n a alors ete decouvert. Il est isotype de sr 2tao 3n dont la structure cristalline et electronique est reportee. Cet oxynitrure de type k 2nif 4 possede un reseau anionique partiellement ordonne, inedit. L'origine de sa couleur orange vif est un mecanisme de transition bande a bande (bv / bc). Le role determinant de l'azote dans la couleur est confirme par des calculs de structure de bande sur un ensemble de nitrures et oxynitrures : par rapport a l'oxyde, la presence des orbitales 2p de l'azote au sommet de la bande de valence retrecit la bande interdite et la couleur des oxynitrures evolue du blanc au jaune, a l'orange, au rouge puis au brun selon la valeur du gap. Dans les systemes ln-w-o-n, deux familles d'oxynitrures de structure apparentee a la fluorine ont ete decouvertes a partir des oxydes ln 1 4w 4o 3 3 (formulation de type fluorine a 4x 7. 3 3@ 0. 6 7, a : cations, x : anions) et ln 6wo 1 2 (a 4x 6. 8 5@ 1. 1 5). Ces oxynitrures forment des domaines de solution solide entre l'oxyde de depart et un oxynitrure de formulation limite a 4x 6@ 2. La structure des tungstates ln 6wo 1 2 (ln : y, ho) a ete precisee. On montre que les oxynitrures a 4x 6@ 2 correspondants possedent une structure tres proche de la fluorine. La gamme de couleur des oxynitrures s'etend du jaune pale au marron et kaki, respectivement, pour les series ln 1 4w 4o xn y et ln 6wo xn y, lorsque la teneur en azote croit. On trouve, pour des compositions intermediaires, des poudres de couleur jaune vif prometteuses dans la perspective d'une utilisation comme pigments colores.
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Nadouf, Mohammed. "Synthese et etude de poudres submicroniques de titanate de baryum et de ses solutions solides avec le strontium." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13129.
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On etudie les solutions solides entre titanate de baryum et titanate de strontium. Deux methodes de synthese de ces perovskites sont abordees : la methode ceramique classique, ou l'on fait reagir des solides a haute temperature, et la methode oxalique qui fait intervenir la preparation d'un sel mixte que l'on decompose a basse temperature. Les relations entre la nature des sels des oxydes, le ph de precipitation, la temperature de reaction ou de precipitation et les caracteristiques structurales et proprietes physiques des ceramiques frittees sont etudiees
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Zschornak, Matthias. "Defect-induced local electronic structure modifications within the system SrO - SrTiO3 - TiO2." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2015. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-169703.
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Owing to their versatile orbital character with both local and highly dispersive degrees of freedom, transition metal oxides span the range of ionic, covalent and metallic bonding. They exhibit a vast diversity of electronic phenomena such as high dielectric, piezoelectric, pyroelectric, ferroelectric, magnetic, multiferroic, catalytic, redox, and superconductive properties. The nature of these properties arises from sensitive details in the electronic structure, e.g. orbital mixing and orbital hybridization, due to non-stoichiometry, atomic displacements, broken symmetries etc., and their coupling with external perturbations.
In the work presented here, these variations of the electronic structure of crystals due to structural and electronic defects have been investigated, exemplarily for the quasi-binary system SrO - SrTiO3 - TiO2. A number of binary and ternary structures have been studied, both experimentally as well as by means of electronic modeling. The applied methods comprise Resonant X-ray Scattering techniques like Diffraction Anomalous Fine Structure, Anisotropy of Anomalous Scattering and X-ray Absorption Fine Structure, and simultaneously extensive electronic calculations by means of Density Functional Theory and Finite Difference Method Near-Edge Structure to gain a thorough physical understanding of the underlying processes, interactions and dynamics.
It is analyzed in detail how compositional variations, e.g. manifesting as oxygen vacancies or ordered stacking faults, alter the short-range order and affect the electronic structure, and how the severe changes in mechanical, optical, electrical as well as electrochemical properties evolve. Various symmetry-property relations have been concluded and interpreted on the basis of these modifications in electronic structure for the orbital structure in rutile TiO2, for distorted TiO6 octahedra and related switching mechanisms of the Ti valence, for elasticity and resistivity in strontium titanate, and for surface relaxations in Ruddlesden-Popper phases.
Highlights of the thesis include in particular the methodical development regarding Resonant X-Ray Diffraction, such as the first use of partially forbidden reflections to get the complete phase information not only of the tensorial structure factor but of each individual atomic scattering tensor for a whole spectrum of energies, as well as the determination of orbital degrees of freedom and details of the partial local density of states from these tensors.
On the material side, the most prominent results are the identification of the migration-induced field-stabilized polar phase and the exergonic redox behavior in SrTiO3 caused by defect migration and defect separation.
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Kirchner, Martin. "Existenzbereiche und physikalische Eigenschaften metallreicher Perowskite (SE3X)M (SE = Seltenerd-Metall; X = N, O; M = Al, Ga, In, Sn): Mit Ergänzungen zu den ternären Systemen EA-In-N (EA = Ca, Sr, Ba)." Doctoral thesis, Technische Universität Dresden, 2005. https://tud.qucosa.de/id/qucosa%3A24696.
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Die Existenz metallreicher Perowskite der Zusammensetzung (SE3X)M (X = O, N; SE = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Er, Ho, Tm, Lu; M = Al, Ga, In, Sn) wurde untersucht. Die Charakterisierung der Proben erfolgte mit Röntgenpulverdiffraktometrie und Elementaranalysen (O und N). Oxide (SE3O)Al mit SE = La, Ce, Pr, Nd und Sm und (SE3O)In mit SE = Ce, Pr und Nd wurden erhalten. Die Reihe der Verbindungen (SE3N)Al (SE = La, Ce, Pr, Nd, Sm) wurde um die Seltenerd-Metalle SE = Gd, Tb, Dy, Ho, Er und Tm erweitert. Die metallreichen Perowskite (SE3N)Sn (SE = La, Ce, Pr, Sm) und (SE3N)Ga (SE = Ce, Pr, Sm, Gd, Tb) wurden erstmals beschrieben. Die thermische Stabilität (DSC) der Phasen (SE3X)M ist für die Nitride allgemein am höchsten. Nitride von Al und Ga zersetzen zwischen 1000 °C und 1200 °C, Stannide bleiben bis 1250 °C thermisch stabil. Messungen der magnetischen Suszeptibilität und der LIII-Absorbtionskanten sind in Einklang mit einer Elektronenkonfiguration SE3+. Die gemessenen elektrischen Widerstände sind charakteristisch für schlechte metallische Leiter. Verschiedene Gehaltschnitte SE3Al-(SE3X)Al und SE3In-(SE3X)In wurden mit Röntgenpulverdiffraktometrie und DTA untersucht. Die Oxide und Nitride (SE3X1-y)M (SE = La, Ce; X = N, O) weisen nur geringe Phasenbreiten auf. Die Carbide (Ce3C1-y)In zeigen hingegen signifikante Phasenbreiten. In den Systemen EA-In-N wurden röntgenografisch phasenreine Pulver von (Ca4N)[In]2 und (EA19N7)[In4]2 (EA = Ca, Sr) erhalten. Durch Elementaranalysen auf H, C, N, O, EA und In und Neutronenbeugung am Pulver können alternative Zusammensetzungen mit einer ausgeglichenen Ladungsbilanz im Sinne des Zintl-Konzepts für diese Phasen ausgeschlossen werden. Im System La-Al wurde die neue Phase La16Al13 beobachtet und an Einkristallen sowie an Pulvern charakterisiert. Das in der Literatur im Cu3Au-Strukturtyp beschrieben kubische Polymorph von Ce3Al wurde auf einen ternären metallreichen Perowskit (Ce3X)Al zurückgeführt.
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Ferrara, Chiara. "Solid State NMR studies of functional oxides." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2014. http://tel.archives-ouvertes.fr/tel-00956577.
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The functional oxides are performing materials showing interestant properties. The study of the local environment respect to the average struvture is essential for the deep understanding of the correlations between structure and properties ; this investigation of short and medium range can be performed with the use of solid state NMR techniques. In particular in this thesis three different classes of materials for applications in fields of optic and energy are considered : perovskite structure LaSrAlO4, the melilite system LaSr(Ga/Al)3O7 and the family of orthosylicates Li2(Fe/Mn)SiO4.
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Frison, Jean-Claude. "Cristallogenèse et caractérisations d'oxydes supraconducteurs du système Tl-Ba-Ca-Cu-O." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1990. http://tel.archives-ouvertes.fr/tel-00170306.
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Les cristaux de phases supraconductrices de formulation générale, TlmBa2Can-1CunO2n+m+2 (avec m=1, 2 et n=1, 2, 3) ont été préparés par une technique de croissance en flux. Chaque phase a été caractérisée par diffraction X (Weissenberg, Buerger, cristal tournant) et par micro-spectroscopie Raman. L'analyse par microsonde électronique a révélé des déficits cationiques par rapport a la formulation idéale. Une étude par HREM a montré dans la plupart des cristaux l'absence d'intercroissance à l'échelle atomique. La température critique a été mise en évidence par mesures électriques, mesures sous champ magnétique continu et susceptibilite alternative. Le comportement magnétique révèle une très forte anisotropie entre les propriétés supraconductrices dans la direction de l'axe c et dans le plan (a, b) (Hc1(c)/Hc1(a,b)=1000 pour la phase 2212). Les courbes d'effet Meissner et d'effet d'écran révèle que l'aimantation est réversible près de Tc et irréversible a plus basse température. La ligne d'irréversibilite (H*, T*) a été caractérisée pour la phase 2212.
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Oliveira, Gonçalo Nuno de Pinho. "Local Probing Spinel and Perovskite Complex Magnetic Systems." Doctoral thesis, 2017. https://repositorio-aberto.up.pt/handle/10216/103096.
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Oliveira, Gonçalo Nuno de Pinho. "Local Probing Spinel and Perovskite Complex Magnetic Systems." Tese, 2017. https://repositorio-aberto.up.pt/handle/10216/103096.
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Sharma, Astha. "Perovskite-silicon tandem based photoelectrochemical systems for efficient solar hydrogen generation." Phd thesis, 2021. http://hdl.handle.net/1885/249071.
Full textAbstract:
Direct solar hydrogen generation(DSTH) is a promising method for renewable hydrogen generation, where solar energy drives the generation of hydrogen and oxygen by molecular dissociation of water on a catalytic or semiconductor surface. Despite an enormous amount of work over the last few decades, DSTH has not yet been implemented on large scale due to low efficiency and high costs. This thesis investigates perovskite-silicon tandem PV and Earth abundant catalysts-based system for low-cost and high-efficiency direct-solar-hydrogen-generation. The thesis starts by identifying performance limitations and conceptualising practical device designs to improve the STH efficiency towards 20%. We develop a new theoretical framework to quantify and compare different loss mechanisms in photovoltaic(PV) based solar hydrogen generation systems and evaluate the potential of different loss mitigation techniques to improve the solar to hydrogen generation efficiency.
Our analysis shows that the two largest losses in an ideal system are energy lost as heat in the photovoltaic component, and current and voltage mismatch between the PV and electrochemical (EC) components due to sub-optimal system configuration. Employing loss mitigation techniques targeting the two major efficiency losses results in predicted STH efficiencies above 20%, without the need for further improvement of the photovoltaic devices or catalyst. These results demonstrate where best to target interventions to mitigate the biggest losses and ensure maximum improvement in the performance. To achieve the STH target set by the DOE for the year 2020, we develop a system with perovskite-silicon tandem PV and Ni based Earth abundant catalysts with a record STH efficiency of 20%. The NiMo electrodes with a high density of NiMo active sites are fabricated in a flower-stem morphology and exhibit an exceptional HER performance. In addition, an improved perovskite top cell with a record open circuit voltage is achieved using n-dodecylammonium bromide. Further analysis is performed to assess the potential for improvement in the STH efficiency. With Si solar cell performance already close to theoretical limits, perovskite solar cell offer opportunities of improvement to improve the tandem performance. Improving the performance of perovskite solar cell alone could improve the STH efficiency to 25%. A technoeconomic analysis is performed to assess the cost competitiveness of the developed system. The levelized cost of hydrogen (LCOH) of DSTH system is calculated as $4.12/Kg. Combining efficiency improvements with projected cost reduction could further reduce the LCOH to $2.3/Kg, presenting a remarkable opportunity to realise cheap renewable hydrogen. Moving towards the aim of a fully integrated system for direct solar hydrogen generation, we develop a photoelectrochemical system based on perovskite PV and Si photocathode system in tandem configuration. We demonstrate a high-performance Si photocathode, incorporating state-of-the-art charge selective passivation and Earth abundant catalysts, with an ABPE of over 10%. Charge selective passivation layers improve the Si photocathode performance by roughly 70% compared to Si photocathode without any passivation, highlighting the importance of the efficiency loss due to recombination at the Si/catalyst interface. An overall water splitting efficiency of 17% is achieved for the photoelectrochemical system when combined with a previously reported Earth abundant OER catalyst and a wide bandgap perovskite solar cell in tandem.
These results show that perovskite-silicon tandem based photoelectrochemical systems have the potential to make large scale direct solar hydrogen generation a reality. This work will encourage dedicated research with a clear awareness of components and system design that needs to be focused on, towards achieving the aim of low-cost, large scale solar hydrogen generation.
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Scalerandi, Francesca. "Use of mixed halide perovskite to achieve highly directional emission by self-alignment of microstructure-emitter systems." Master's thesis, 2021. https://hdl.handle.net/10216/139576.
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Su, Shi-xin, and 蘇世昕. "Investigation in Fabrication Process and Electrical Properties of (Na,K)NbO3-based Multi-component Oxide Systems With Perovskite Crystal Structures." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/54162168968949320510.
Full textAbstract:
碩士義守大學
材料科學與工程學系碩士班
97
Sodium and potassium niobate 〈(Na,K)NbO3〉 is currently believed to be one of piezoelectric materials for replacing the lead-containing Pb(Zr,Ti)O3 from environmental concerns. However, there are so many problems for manufacturing (Na,K)NbO3-containing piezoelectric materials. For example, how to improve its sinterability to further increase its densification is one major task for improving the property of (Na,K)NbO3. Therefore, this research is concentrated on the process improvement of fabricating (Na,K)NbO3 ceramics. There are five different process for sintering (Na,K)NbO3 materials through various initial materials; the first process is obtained from the combinations of Nb2O5 and carbonate salts; the second, Nb2O5 and nitrate solution; the third, Nb2O5 and hydroxide solution; the fourth, nitrate and chloride solutions; the last one, additions of BaTiO3. It is expected that the key points in densification problem of (Na,K)NbO3 can be further solved. From experimental results, it is found: the optimal calcinations temperature in the carbonate system is 950℃; 500℃ in the nitrate system; 500℃ in the hydroxide system; and 350℃ in the nitrate and chloride aqueous solution. Optimal sintering temperature is found to be 1100℃ in the carbonate system; 1050℃ in the nitrate system; 800℃ in the hydroxide system; 1050℃ in the nitrate and chloride aqueous solution; 1050℃ for 0.05% BaTiO3 alloying systems, but 1150℃ for ≧0.10% BaTiO3 alloying systems. As to the densification, the best bulk density of sintering (Na,K)NbO3 ceramics is 3.536g/cm3 in the carbonate system; 3.613g/cm3 in the nitrate system; 2.475g/cm3 in the hydroxide system; but only 3.120g/cm3 in the nitrate and chloride aqueous solution. Overall, from the densification, the nitrate system is found to be the best process for fabricating (Na,K)NbO3 ceramics in this research.
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Scholz, Julius. "Hybrid systems of molecular ruthenium catalyst anchored on oxide films for water oxidation: Functionality of the interface." Diss., 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3F56-7.
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(9525959), Reza Asadpour. "EXPLORING THE POTENTIAL OF LOW-COST PEROVSKITE CELLS AND IMPROVED MODULE RELIABILITY TO REDUCE LEVELIZED COST OF ELECTRICITY." Thesis, 2020.
Find full textAbstract:
The manufacturing cost of solar cells along with their efficiency and reliability define the levelized cost of electricity (LCOE). One needs to reduce LCOE to make solar cells cost competitive compared to other sources of electricity. After a sustained decrease since 2001 the manufacturing cost of the dominant photovoltaic technology based on c-Si solar cells has recently reached a plateau. Further reduction in LCOE is only possible by increasing the efficiency and/or reliability of c-Si cells. Among alternate technologies, organic photovoltaics (OPV) has reduced manufacturing cost, but they do not offer any LCOE gain because their lifetime and efficiency are significantly lower than c-Si. Recently, perovskite solar cells have showed promising results in terms of both cost and efficiency, but their reliability/stability is still a concern and the physical origin of the efficiency gain is not fully understood.
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周發秦. "Structure refinement of double perovskite Ca2-2XSr2XFeMoO6 system and the relationship." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/82667692872667197682.
Full textAbstract:
碩士東海大學
物理學系
89
We report the structural, electrical and magnetic properties and the relationship to physical properties of the double perovskite Ca2-2XSr2XFeMoO6（X = 0.0 ~ 1.0）system. Rietveld refinements were used to accomplish the structural analyses of these samples. With increasing X content, the structure changes from Monoclinic（X = 0.0 ~ 0.15）to Orthorhombic（X = 0.2 ~ 0.3）to Tetragonal（X = 0.4 ~ 1.0）.The volume V of unit cell are increasing as X is increasing from 0 to 1. We also get tolerance factor t from the structure refinement, and t is increasing as X is increasing from 0 to 1. In electrical properties, compounds of the Ca2-2XSr2XFeMoO6 are metallic. Their magnetic properties are ferromagnetic. TC and TP are increasing as X increases from 0 to 1. We also find the relationship between tolerance factor t and physical properties.
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Huang, Tzu-Wei, and 黃子瑋. "The Dielectric Properties of Perovskite Oxide of La1-xKxCo1-xNbxO3 System." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/01557460345874570452.
Full textAbstract:
博士國立成功大學
材料科學及工程學系碩博士班
96
In this study, lanthanide oxides LaCoO3 with perovskite structure (ABO3) is used as the substrate and KNbO3 is added to prepare La1-xKxCo1-xNbxO3 (x = 0 to 1) ceramic powder by solid state reaction with a view to replace La with K and Co with Nb to study the effect of K and Nb on microstructure and electrical properties of LaCoO3 perovskite structure. Meanwhile, through different content of x and sintering conditions, ceramic dielectric properties are studied as well. The results show the success of synthesizing ferroelectric ceramic composite system La1-xKxCo1-xNbxO3 with two-stage solid-state reaction. All the specimens form a single perovskite structure after two hours of sintering at 1400 °C. When adding amount is less than 0.1 (0.1 < x), the crystal structure is rhombohedral. When adding amount is between 0.1 and 0.7 (0.1 ≦ x ≦ 0.7 ) the crystal structure transforms into cubic. When adding amount is greater than 0.7 (0.7 < x), the crystal structure transforms into the orthorhombic. By DSC analysis, the activation energy of crystallization of the powders with x = 0.1 and 0.3 are 121.75 and 116.82 kJ/mol respectively, x = 0.5 and 0.7 are 111.89 and 106.96 kJ/mol respectively. The calculation result of XRD when x = 1 using Rietveld method shows the values of wRp, Rp and X2 are 0.0345, 0.0277, and 1.28 respectively, and its chemical formula: La0.91K0.09Co0.89Nb0.11O3.12 is consistent to the formula La1-xKxCo1-xNbxO3 that we have set, which represents most of the K, Nb, La and Co ions exist in the state of monovalent, quinquevalent, and trivalent respectively in this system. The space group of La1-xKxCo1-xNbxO3 synthesized in this experiment whose ceramic structure is cubic is , in which a = 3.88 Å α = 90°. Observed in TEM analysis, when adding amount x = 0.1, the lattice constant a = 3.89 Å. Meanwhile, in the selected-area-diffraction (SAD) patterns along [001] direction, the super-lattice structure of (100) plane is identified, and in SAD patterns along the [011] and [ ] direction, super-lattice structures of ( ) and ( ) plane are also discovered. La1-xKxCo1-xNbxO3 flaccid ferroelectric ceramics is the grain boundary layer capacitance composed of semi-conductive process gains and high-resistance grain boundaries , at room temperature, x = 0.1 sample sintered at 1400°C for two hours will have the dielectric constant (E) of approximately 58,000 and dielectric loss (tan δ) of approximately 0.8. Based on the Arrhenius equation, The activation energy of the dielectric relaxation is estimated to be 5.88 kJ/mol and the lattice vibrational phonon frequency τ0 is 1.881 × 10-3 s. From XPS analysis results, La exists in the state of trivalent ions in La1-xKxCo1-xNbxO3 system. When the adding amount x = 0.1, Co exists in the state of trivalent cation. In order to form an ABO3 structure, K+ only replaces the La3+ in A position; Nb exists only in the state of quinquevalent in the system.
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Gong, Shi-Zong, and 龔世宗. "Structural and magnetic properties of La0.7Pb0.3Mn1-xCoxO3+δ(x = 0.0 ~ 1.0)perovskite-like system." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/60703285211581506637.
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Behera, Sukanti. "Thermoelectrics and Oxygen Sensing Studies of Selected Perovskite Oxides." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2975.
Full textAbstract:
Perovskite oxides show wide range of applications in the area of magnetism, ferroelectricity, piezoelectricity, thermoelectricity, gas sensing, catalyst development, solid oxide fuel cell, etc. This is due to flexibility in the structure and compositions that can be tuned by specific element doping. In the perovskite oxide (ABO3), large cation (A) is 12 -coordinated and smaller B-cation is 6 coordinated with oxide ions. Oxide materials are considered as better candidates for thermoelectric applications (interconversion of thermal into electrical energy) due to its non-toxicity and thermal stability at elevated temperature. These are insulating in nature and the conductivity can be increased by doping A and / or B –sites. Perovskite oxides are also used for oxygen monitoring in different applications including control and optimization of combustion of fossil fuels in industries and automobiles, biological and defines places, etc.
In the present study, we focused on thermoelectric properties in single perovskite oxides of lanthanum cobaltite and calcium manganite and a double perovskite oxide of dysprosium barium cobaltite. Also, the oxygen sensing behaviour of dysprosium barium cobaltite at elevated temperatures is studied. The thesis contains seven chapters and a summary of respective chapters are given below.
The first chapter outlines the basics of thermoelectric and gas sensing applications of both perovskite and double perovskite oxides. In the initial part, thermoelectric phenomena are explained. Thermoelectric effect is the conversion of thermal energy to electrical energy and vice-versa. Higher thermoelectric efficiency
(η) can be achieved by maintaining a large temperature difference across the material. The efficiency depends on the thermoelectric figure of merit (zT) of material, which depends on thermopower (S), electrical resistivity (ρ) and thermal conductivity
(κ) of the material and hence needs to be optimized. The latter part discusses the oxygen sensing property of distorted double perovskite 112 structure type as it shows advantages over other materials due to oxygen nonstoichiometric. Further, an overview of the relevant literature, objective and scope of the thesis are mentioned.
The second chapter elucidates the materials and methods used for the present work. The materials viz. LaCoO3, CaMnO3-δ and DyBaCo2O5+δ, were selected for thermoelectric and oxygen sensing studies. Both the conventional solid state and soft chemistry methods were adopted for the synthesis of these materials. Powders were densified into pellets by hot uniaxial pressing / cold isostatic pressing and various heat treatments were carried out. Samples thus prepared were phase pure as confirmed using powder x-ray diffraction and Rietveld refinement performed for structural analysis. Morphological studies were carried out using scanning electron microscopy and transmission electron microscopy. Further Raman and x-ray photoelectron spectroscopic characterization of these materials were discussed. The transport properties viz. electrical resistivity, thermopower and thermal conductivity of compact pellets were measured at elevated temperatures. Further, the home-built apparatus for room temperature See beck measurements and chemo resistive oxygen sensing were explained in detail as a part of this work.
The third chapter describes the effect of monovalent ion doping (Na+ and K+) at A-site of lanthanum cobaltite on thermoelectric properties. Lanthanum cobaltite system exhibit exotic behaviour due to commensuration phenomena of spin, lattice, charge and metal insulator transition. The synthesis, followed by structural refinements by Rietveld method using Fullprof suit program are explained. The results of the transport properties indicate that there is no appreciable change in the See beck Coefficient of K-doped samples throughout the studied temperature range.
The Na-doped samples exhibit a decrease in the Seebeck value with increasing Na content at room temperature. At higher temperatures Seebeck value matches with that of the parent sample. This may be due to a change in the ratio of the concentration of Co4+/Co3+ ions which increases the configurational entropy of the system. In conclusion, the highest figure of merit (0.01) found for the Na / K- doped lanthanum cobaltite is for 15 atomic wt. % of doping amongst the studied samples.
The fourth chapter explains about Tb/Nb co-doped calcium manganite for thermoelectric applications. The CaMnO3-δ shows enhanced thermoelectric properties, exhibits n-type behavior and the absolute thermopower is found to be 129 µV/K. Here, we investigated the Terbium and Niobium codoped at Ca and Mn-sites respectively. The presence of oxygen non-stoichiometry was confirmed using Raman spectroscopy (Mn3+ peak at 614 cm-1) and δ value was evaluated by iodometric titration. The thermoelectric properties of cold isostatic pressed (CIP) pellets prepared by the solid state and soft chemistry routes are compared. The non-monotonous behavior of absolute thermopower may be due to the increase of Mn3+ in the Mn4+ matrix and also the presence of oxygen defects in compounds. The thermoelectric figure of merit of solid state sample CaMnO3-δ estimated of 0.036 at 825K.
The fifth chapter describes the thermoelectric properties of double Perovskite AA’B2O6 (112 type): (RE)BaCo2O5+δ. It is a disordered double perovskite with non-stoichiometry in oxygen and exhibits mixed valences of Cobalt. Resistivity of DyBaCo2O5+δ was found to be 0.09 Ω cm and Seebeck coefficient is found to be 42 µV/K. In order to improve the thermopower value, the Fe is substituted at Co-site. This varies the valences of Cobalt that in turn leads to a higher thermopower. Also, the morphology of thermally etched CIP pellets recorded and correlated with the transport properties. It shows the highest thermoelectric figure of merit of 0.25 at 773 K for 20 at wt % of Fe substituted sample.
The sixth chapter explains about oxygen sensing studies of DyBaCo2O5+δ (112 type). The detailed structural and morphological characterization studies were carried out. Thermogravimetric analysis at isothermal temperature 873 K shows fast intake/release of oxygen of this disordered double perovskite structure. The higher chemo resistive oxygen sensitivity at the elevated temperature was measured. Further, the systematic study on the effect of oxygen sensing on the substitution of Fe and Cu at Co-site in DyBaCo2-xM xO5+δ was investigated. The possible bulk diffusion mechanism at higher temperature due to movement of oxygen defects were explained. The highest sensitivity was obtained for x = 0.4 at % of Fe and 0.2 at % of Cu at 973 K and 823 K respectively.
The key findings and future aspects are summarized in the chapter-7.
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Kothai, V. "On the Factors Influencing the Stability of Phases in the Multiferroic System BiFeO3-PbTiO3." Thesis, 2015. http://etd.iisc.ernet.in/2005/3949.
Full textAbstract:
Rhombohedral perovskite BiFeO3 is a single phase multiferroic compound exhibiting both magnetic (Neel temperature ~370˚C) and ferroelectric (Curie point ~840˚C) ordering well above the room temperature. Ferroelectricity in BiFeO3 is due to
stereochemically active 6slone pair in Biion which causes large relative displacements of Bi and O ions along the [111] direction. Long range spiral modulation of the canted antiferromagnetic spin arrangement in Feeffectively cancels the macroscopic magnetization due to Dzyaloshinskii–Moriya interaction and thereby prevents linear magneto-electric effect. Synthesizing dense pure BiFeO3 by conventional solid state method is difficult due to the formation of thermodynamically stable secondary phases such as Bi2Fe4O9, Bi25FeO39 and Bi46Fe2O72. To stabilize the perovskite phase and to suppress the cycloid several groups have adopted different strategies such as thin film growth, different synthesis methods and chemical substitution. Of the various substitutions reported in the literature, PbTiO3 substitution has shown very interesting features, such as (i) unusually large tetragonality (c/a~1.19), (ii) formation of morphotropic phase boundary (MPB) and (iii) high curie point Tc~650C. MPB ferroelectric systems such as lead zirconate titanate (PZT) are known to exhibit high piezoelectric response due to the coupling between strain and polarization. Hence the existence of magnetic ordering in BiFeO3-PbTiO3 offers an interesting scenario where polarization, strain and magnetization may couple together. The high Curie point also makes the system an interesting candidate for high temperature piezoelectric application. However its potential as a high temperature piezoelectric material has not been realized yet. A detailed review of literature suggests a lack of clear agreement with regards to the composition range of the reported MPB itself. Different research groups have reported different composition range of MPB for this system even for almost similar synthesis conditions.
The present thesis deals with broadly two parts, firstly with the preparation of pure BiFeO3 by co-precipitation and hydrothermal methods and its thermal stability and secondly resolving the cause of discrepancy in range of MPB reported in BiFeO3-PbTiO3 solid solution. Detailed examination of this system (BiFeO3-PbTiO3) around the reported MPB composition by temperature dependent X-ray, electron and neutron diffraction techniques, in conjunction with a systematic correlation of sintering temperature and time with microstructural and phase formation behavior revealed the fact that the formation of MPB or the single ferroelectric phase is critically dependent on the grain size. This phenomenon is also intimately related to the abnormal grain growth in this system.
Chapter 1 gives the brief overview of the literature on the topics relevant to the present study. The literature survey starts with a brief introduction about the perovskite oxides; their ferroelectric, magnetic and multiferroic properties were discussed in further sections. A brief outline on the grain growth mechanism is described. An overview of BiFeO3 and various synthesis methods, different chemical substitutions and their effect on properties are provided. A brief review of published literature on BiFeO3-PbTiO3 solid solution and its properties is also presented.
Chapter 2 deals with the synthesis of pure BiFeO3, heat treatment and characterisation. BiFeO3 was synthesised by (a) co-precipitation and (b) hydrothermal methods. In co-precipitation method, calcination of precipitate at different temperature resulted in the formation of BiFeO3 along with secondary phases (Bi2Fe4O9 and Bi24FeO39). The optimum calcination temperature to prepare pure BiFeO3 was found to be 560C. The synthesized pure BiFeO3 exhibits weak ferromagnetic hysteresis at room temperature, the degree of which increases slightly at 10K (-263C). The hydrothermal treatment was carried out in (a) carbonate and (b) hydroxide precipitates with KOH as mineralizer. BiFeO3 prepared using hydroxide precipitate was stable till 800C whereas with carbonate precipitate it was stable only till 600C.
Chapter 3 deals with the stability of phases in (1-x)BiFeO3 -(x)PbTiO3 solid solution. Samples prepared by conventional solid state route sometimes remain as dense pellet and on certain occasions it disintegrate completely into powder observed after sintering. Irrespective of the composition, sintering time and temperature, powder X-ray Diffraction (XRD) pattern of the survived pellet (crushed into powder) shows coexistence of rhombohedral (R3c) and tetragonal (P4mm) phases and the disintegrated powder (without crushing) show 100% tetragonal (P4mm) phase. Very high spontaneous tetragonal strain (c/a-1) ~0.19 at MPB is believed to be the origin for disintegration. But in all the survived pellets at least a minor fraction of rhombohedral phase (5-7%) is present. Systematic sintering studies with the time and temperature shows, decreasing the sintering temperature and time will increase the lifetime of the pellet and by increasing the sintering temperature and time the pellet will disintegrate. In this work we have conclusively proved that the wide composition range of MPB reported in the literature is due to kinetic arrest of the metastable rhombohedral phase and that if sufficient temperature and time is given, the metastable phase disappears. The suppression/formation of minor rhombohedral phase is expected due to the play of local kinetic factors during the transformation process. This makes the system behave in an unpredictable way with regard to the fraction of rhombohedral phase that is observed at room temperature.
A systematic X-ray and neutron powder diffraction study of the giant tetragonality multiferroic (1-x)BiFeO3 -(x)PbTiO3 have shown that the compositions close to the morphotropic phase boundary of this system present two different structural phase transition scenarios on cooling from the cubic phase: (i) Pm3m P4mm(T2)+P4mm(T1)
P4mm (T1) and (ii) Pm3m P4mm(T2) + P4mm(T1) + R3c P4mm (T1) + R3c. The comparatively larger tetragonality of the T1 phase as compared to the coexisting isostructural T2 phase is shown to be a result of significantly greater degree of overlap of the Pb/Bi-6s and Ti/Fe-3d with the O-2p orbitals as compared to that in the T2 phase. High temperature electron diffraction studies show that the metastable rhombohedral phase is present in the cubic matrix well above the Curie point as nuclei. Life time of the metastable R3c nuclei is very sensitive to composition and temperature, and nearly
diverges at x → 0.27. MPB like state appears only if the system is cooled before the metastable R3c nuclei could vanish.
Issue of the metastable rhombohedral state is developed further in Chapter 4. A one-to-one correlation was found between the grain size and phase formation behavior. Fine grained (~1µm) microstructure (usually pellets) shows phase coexistence (R3c+P4mm) and the disintegrated coarse grains (~10µm) show tetragonal (P4mm) phase. Microstructural analysis revealed the disintegration was caused by abnormal grain growth along with the disappearance of metastable rhombohedral phase. Abnormal grain growth starts at the periphery/crack i.e., at the free surface and move towards the canter of the pellet. Size reduction of disintegrated coarse grains (~10µm) to fine grains (~1µm) by crushing the sample showed that the system switching form pure tetragonal (P4mm) state to the MPB state comprising of tetragonal and rhombohedral phases (R3c+P4mm). In another approach the smaller sized particles of x=0.20 were synthesized by sol gel method. It was reported that in conventional solid state route x=0.20 exhibits pure rhombohedral phase. The sol-gel sample calcined at 500C (particle size ~15nm) stabilizes tetragonal metastable phase along with the stable rhombohedral phase, the morphotropic phase boundary state. Samples calcined at higher temperature, 800C (particle size ~50nm) also showed stable rhombohedral phase. Ferromagnetic behavior was observed in the sample having phase coexistence and the sample with pure rhombohedral phase showed antiferromagnetic behavior. Hence this material is a promising candidate which can be tuned to exhibit different behavior just by adopting different grain size.
Chapter 5 deals with the magnetic structure of (1-x)BiFeO3 -xPbTiO3 solid solution with change in composition and temperature. Magnetic structure was studied using powder neutron diffraction in the composition range x=0.05 -0.35. Rietveld analysis was carried out for the nuclear and magnetic phases, by considering R3c phase for the nuclear structure. To account for the magnetic Bragg peak at d=4.59Å, three antiferromagnetic models were considered for the magnetic structure: (i) helical spin arrangement as in BiFeO3, (ii) commensurate G-type antiferromagnetic ordering with moments in the a-b plane (of the hexagonal cell), and (iii) commensurate G-type ordering with moments parallel to the c-axis (of the hexagonal cell). The third model was found to be suitable to explain the magnetic peak accurately and the better fitting of magnetic peak was observed in this model compared to others. At room temperature the MPB compositions have rhombohedral and tetragonal nuclear phases along with the rhombohedral magnetic phase. Addition of PbTiO3 in BiFeO3 not only changes the
magnetic structure but also reduces the magnetic moment due to the substitution of Ti in Fesite. High temperature neutron diffraction studies reveal the magnetic transition at ~300C for x=0.20, ~95C for x=0.27 and ~150C for x=0.35. The Neel temperature observed in neutron diffraction studies were also confirmed by DSC and by temperature dependent dielectric studies. For x=0.20, anomalous variation in the lattice parameters and the octahedral tilt angle was observed across the magnetic transition temperature. In the magnetic phase, the c-parameter was contracted and the octahedral tilt angle slightly increased. This result suggests a coupling between spin, lattice and structural degrees of freedom around the transition temperature. Temperature dependent powder neutron diffraction study at low temperature from 300K (27C) to 4K (-269C) in x=0.35 shows the evolution of tetragonal magnetic phase at 200K (-73C) whose intensity is increasing with decrease in temperature. Below 200K, x=0.35 has rhombohedral and tetragonal magnetic and nuclear phases. While in x=0.27 at low temperature, rhombohedral magnetic and nuclear phases are present along with the tetragonal nuclear phase alone (the tetragonal magnetic phase is absent). We propose this discrepancy in the Neel temperature and the magnetic phase formation can be due to the probabilistic nature of the existence of metastable rhombohedral phase which was discussed earlier.
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Guo, An-Zhe, and 郭安哲. "Fabrication of Mixed Halide Perovskite Solar Cells through Ultrasonic Spray Deposition Technique Combined Multi-Channel Pumping Control System." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/c57rtk.
Full textAbstract:
碩士國立中央大學
化學工程與材料工程學系
107
Perovskite solar cells as the most promising material due to low temperature solution processability and low cost have surpassed 20% power conversion efficiency through change element composition. Tuning the composition will change the band gap and the morphology, but it is a complicate procedure to optimize element composition. In general, several composition of precursor must be prepared and tested sequentially. Lack of efficient experimental method to optimize component rapidly. Moreover, it is necessary to develop practical processes that enable the fabrication of up-scale, high-throughput, and high-quality thin films. In this study, perovskite solar cells are fabricated via ultrasonic spray-coated technology combined with multi-channel syringe pump control system. The system provides an experimental method to optimize composition rapidly through adjusting different pumping rates of precursor, and simplifying cumbersome experimental steps and saving raw materials. First, we aim to optimize the halide ratio of CH3NH3PbI3-xBrx precursor based on PbI2, MAI, MABr, and PbI2, PbBr2, MAI respectively. Then, figuring out whether bromide ions from distinguish compounds will have influence on optimizing process. Furthermore, an effective method flash annealing under vacuum is adopted to enhance quality of perovskite thin film with power conversion efficiency of up to 17.1% for small device. Meanwhile, a 70 cm2 high quality perovskite thin film is obtained through optimizing spray-coated parameters and routes with highest efficiency of 17% and 14.95% for average. The process presents a way toward a scalable and industrially compatible manufacturing process capable of creating high-performance perovskite solar cells.
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Chen, Chia-Hung, and 陳佳宏. "Quasi-solid dye-sensitized solar cells integrated with nanomaterials blending gel electrolyte & the optimized process for perovskite solar cell system under atmosphere." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/60982847222517530754.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
104
The first part of this study involves stable qusi-solid state dye synthesized solar cell (QS-DSSC). Polymer gel electrolyte was fabricated by using ionic liquids and a diamine derivative as low molecular mass organogelators (LMOGs). Furthermore, the influence of different nanoparticles such as SiO2, TiO2 and GO to polymer gel electrolyte electrolytes were investigated. In optimizing the photoelectric conversion efficiency of the DSSC with the polymer gel electrolyte is up to 7.21%, which is close to the conversion efficiency of the ionic liquid electrolyte 7.22%. Consequently, the photovoltaic performances of DSSCs based on nano-TiO2 nanocomposite polymer electrolyte gelators are much better than those only polymer gelators. Remarkably, the results of the J-V measurement show a champion of 7.79% power conversion efficiency with NCPE-T. Significantly on successive heating and light soaking stability tests the polymer gel electrolyte and nanocomposite polymer gel electrolyte maintains more than 90% of the original photoelectric conversion efficiency after 10 days, whereas the ionic liquid electrolyte drops to 50%. Intensity modulated photocurrent/photovoltage spectroscopy and electrochemical impedance spectra were conducted to study the kinetic process of electron transport and recombination behavior. The second part is the use of two-step spin-coating method to establish a perovskite solar cell under the atmosphere. With optimizing m-TiO2, PbI2, MAI and HTM layer thickness, the photoelectric conversion efficiency dramatically increase from 0.25% to 8.88%.