Academic literature on the topic 'Europium titanate'

New compounds of sodium samarium titanate Na0.5Sm4.5Ti4O15and sodium europium titanate Na0.5Eu4.5Ti4O15were synthesized successfully by solid state reaction at 1300 oC and 1200 oC, respectively. The lattice parameters of Na0.5Sm4.5Ti4O15and Na0.5Eu4.5Ti4O15were determined at ordinary temperature by using X-ray powder diffraction method. Their Lattice types were determined, and their patterns were indexed. Polycrystalline X-ray diffraction data of sodium samarium titanate were listed. Differences of their crystal structures were analyzed and discussed.

A literature review on the topic of ferroic and multiferroic solid solutions of BaTiO3, SrTiO3 and EuTiO3 forms the first part of this master thesis. The second part describes the experimental preparation and evaluation of the properties of samples of europium strontium titanates - EuxSr1-xTiO3. First, the high temperature solid state synthesis was carried out and relative density and open porosity of the sintered samples were evaluated. The sintered samples showed open porosity higher than 10%. The reasons for this behavior were evaluated and described from the point of view of experimental conditions and thermodynamical calculations. Finally, electric and dielectric properties of selected samples were measured. These results show that these samples are insulators and their residual conductivity is caused probably by oxygen vacancies, arising from the synthesis in a strongly reducing atmosphere of pure hydrogen.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2008.<br>Committee Chair: Sandhage, Kenneth; Committee Member: Barefield, Kent; Committee Member: Bunz, Uwe; Committee Member: Carter, Brent; Committee Member: Tannenbaum, Rina.

Le present travail est consacre a l'etude de guides d'ondes planaires d'oxyde de titane (tio#2), dopes avec des ions erbium et europium, fabriques par le procede sol-gel. La synthese du sol precurseur de tio#2 ainsi que le protocole utilise pour le depot des couches sont decrits en detail. Les proprietes de guidage, obtenues des une temperature d'elaboration relativement basse (100 c), sont utilisees pour suivre la densification de ces guides et pour la determination de leur coefficient d'attenuation. Les parametres optogeometriques (indice de refraction et epaisseur) sont determines par spectroscopie des lignes noires. La rugosite de surface est mise en evidence par microscopie a force atomique (afm). La potentialite du procede sol-gel dans le domaine de l'optique integree est illustree par le matricage de microstructures (reseaux) dans les guides de tio#2. La technique de spectroscopie raman en configuration guidee, est utilisee pour l'etude de la densification de ces guides, notamment pour suivre le processus de cristallisation. Dans le meme but, le dopage avec des ions europium trivalents fournit une information plus locale. Enfin, les proprietes spectroscopiques (fluorescence et durees de vie) de l'ion erbium dans les guides de tio#2, sont etudiees en fonction du taux de dopage (0,1 a 15%) et de la temperature de recuit: l'emission de fluorescence a 1,5 m (#4i#1#3#/#2#4i#1#5#/#2) ainsi que celle de up-conversion sont analysees en configuration guidee. L'influence des groupements hydroxyles sur les declins de fluorescence est suffisamment reduite par un traitement des couches a 600 c. A cette temperature, le maximum de la duree de vie du niveau #4i#1#3#/#2 (4 ms) est atteint dans le cas des guides dopes a 0,1% en ion erbium. Les declins de fluorescence sont ensuite analyses dans l'approximation de judd-ofelt

碩士<br>國立臺南大學<br>材料科學系碩士班<br>100<br>This study were used conventional solid-state reaction technique to prepare the phosphors of Li2TiO3:Eu3+, and doped Eu2O3 to observe the emission characteristic, then co-doped Na+ and K+ to improve its optical property. The research shows that calcined at 800°C for 24 h synthesis phosphors of Li2TiO3: Eu3+ (1 mole%) have better luminescence properties. It has a strongest peak at 394 nm and the second strong peak at 465 nm, the excitation wavelength consistent with the phosphor required. When 394 nm was used as the excitation source, the phosphors emission intensity increased with the time retention to 24 hour to obtain the maximum. The luminescence properties was improved and enhanced for the samples with co-doped sodium and potassium. Co-doped sodium and potassium, the XRD signal of europium oxide is reduced, and Co-doped potassium 10 mole%, shows the best luminescence properties.

EuTiO3 (ETO) is a perovskite-type oxide consisting of divalent Eu and tetravalent Ti. Due to Eu2+ possessing a half-filled 4f shell with a large spin magnetic moment (7 μB), ETO is a magnetic material with localized Eu 4f electrons, which are related to its giant Seebeck coefficient and considerable thermoelectric performance. Crystalline ETO is isostructural with SrTiO3 (cubic, Pm3̅m) on the long-range scale at ambient temperature, but its local structure has a high degree of disorder. In this dissertation, the magnetic Eu2+ was partly substituted by isovalent nonmagnetic alkaline-earth metal cations A (A = Ba2+, Sr2+, Ca2+, and Mg2+). The aims were to synthesize perovskite-type Eu1−xAxTiO3−δ solid solutions and investigate their crystal structures, local structures, electronic band structures, thermoelectric properties, and interrelations among them. All samples were synthesized by using a two-step process including the Pechini method for precursor synthesis and subsequent high-temperature annealing under reducing atmosphere. The combination of crystal structure and transport properties analysis revealed that polycrystalline Eu1−xAxTiO3−δ (A = Ba2+, Sr2+, Ca2+) solid solutions were successfully synthesized in the full compositional range of 0 ≤ x ≤ 1. An exception was the (partial) Mg2+ substitution. It was impossible within the used experimental parameters to obtain a single-phase Eu1–xMgxTiO3 solid solution, resulting from that the ionic radius of Mg2+ is too small to be bonded in an AO12 cuboctahedron. In the case of Sr2+ substitution, the long-range cubic symmetry was maintained in the entire compositional range due to the virtually equal ionic radii of Sr2+ and Eu2+. A minor effect on the electrical conductivity and the ZT values had been achieved by the Sr2+ substitution in a wide compositional range. Promising thermoelectric results were observed for the Ba2+ and Ca2+ substituted samples. The partial substitution of Eu2+ with Ba2+/Ca2+ led to an expansion/contraction of cubic sub-cell volume, resulting in different kinds of lattice defects and local structural distortions. Both Ba2+ and Ca2+ substitutions increased electrical conductivity, decreased lattice thermal conductivity, and hence improved the ZT values. In comparison with Ba2+ substitution, the enhanced thermoelectric performance by Ca2+ substitution was more pronounced at lower temperatures. Since the ionic radius of Ca2+ is smaller than that of Eu2+, the given smaller unit cell induced chemical pressure which facilitated lattice deformations and defect formations (e.g. Eu3+). The resulting impurity levels in the electronic band structure played an important role in the electronic conduction at low temperatures. The pristine ETO sample displayed a glass-like thermal conductivity (κ) at low temperatures, while the Ca2+-rich samples displayed ordinary crystalline κ behavior. The glass-feature of κ was one solid evidence for verifying the local structure disorder of ETO. Due to a large spin moment of Eu2+, magnons as additional heat carriers contributed with a large magnitude to the heat conduction in all Eu2+ containing samples at intermediate temperatures. The temperature-independent large Seebeck coefficient below ambient temperature was ascribed to the magnon-drag effect together with the influence of Eu 4f hybridization and the local structural disorder. The influence of Eu2+ 4f electrons on transport properties was strongly related to crystal structure variations, which was verified through isovalent chemical substitution by A-site cations with different ionic radii. The obtained results demonstrated how by invoking “lattice deformation and local disorder” one can manipulate the electronic transport properties and in parallel reduce intrinsic lattice κ of the perovskite-type ETO oxides. The substitution of Eu2+ with naturally abundant Ca2+ is a promising approach for improving thermoelectric performance and simultaneously reducing the usage of valuable europium.

We are living in an age where the demand for energy is growing rapidly. This means that supplies to easily accessible oil and natural gas is unlikely to keep up with the demand as times goes on. The world will have to use energy more efficiently and increase its use of other sources of energy. This study is aiming at developing materials that will improve the power conversion efficiency of photovoltaic cells by using up and down-converting phosphor materials. ZnTiO3-Zn2TiO4 composite and ZnTiO3 phosphors doped with Er3+,Yb3+, Eu3+ and Al3+, which display up and down-converted luminescence were synthesized by a simple high temperature conventional solid state reaction method. The structure, particle morphology, absorption, photoluminescent properties and elemental distribution were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis-NIR absorption spectrometer, photoluminescence (PL) spectroscopy and time of flight secondary ion mass spectroscopy (TOF-SIMS), respectively. ZnTiO3-Zn2TiO4 composite doped with different concentration of Er3+ ions was synthesized via solid state chemical reaction method at 1100 ℃. The X-ray diffraction (XRD) confirmed the crystallization of both the hexagonal ZnTiO3 and cubic spinel Zn2TiO4 phases of the composite. The SEM images of ZnTiO3-Zn2TiO4:Er3+ composite showed that the particle morphology was made up of faceted hexagons. Furthermore, the ZnTiO3-Zn2TiO4:Er3+ phosphors were excited in the near-infrared (NIR) region using a laser diode with a wavelength of 980 nm and displayed both green and red up-conversion emission bands in the visible range at 543, 553, 650 – 670 nm. These emission bands correspond to 2H11/2, 4S1/2→ 4 I15/2 and 4F9/2→ 4 I15/2 transitions of Er3+ ions. However, the interaction mechanisms involved in the upconversion process of ZnTiO3-Zn2TiO4:Er3+ phosphor is discussed with the help of an energylevel schematic diagram and the number of the photons involved in the up-conversion luminescence process were of a double photon mechanism. The decay lifetimes were studied by fitting the luminescence decay curve with a single-component exponential decay. Er3+ and Yb3+ incorporated zinc titanate (ZnTiO3) phosphor powders were synthesized using conventional solid-state reaction method at 800 ℃. A ZnTiO3:Er3+,Yb3+ phosphor that resembled an ecandrewsite single phase with space group R-3 (148) was obtained, as proven by X-ray diffraction (XRD). The SEM image showed a surface morphology composed of agglomerated irregular shaped particles. The energy band gap of ZnTiO3 was engineered by incorporating different concentration of the dopant ions. After irradiating ZnTiO3:Er3+with a 980 nm laser beam, the phosphor up-converted the photon energy to display green and red emissions in the visible range that were positioned at 527, 545 and 665 nm. Enhancement of the luminescence intensity of ZnTiO3:Er3+ phosphor was achieved by variation of Er3+ concentration. Co-doping with Yb3+ ions proved to be effective in enhancing the luminescence intensity of the optimized Er3+ ion emission and new emission bands at 410 and 480 nm, through an energy transfer mechanism were observed. The enhancement of the lifetime of the up-conversion luminescence was also achieved by co-doping ZnTiO3:Er3+ phosphor with Yb3+ ion. The energy transfer mechanisms involved in Er3+ - Yb3+ co-doped ZnTiO3 phosphor was illustrated and discussed in detail. The ZnTiO3:Er3+, Yb3+ thin films were successfully deposited by pulsed laser deposition (PLD) by varying the silicon (100) substrate temperature. The distribution of the ions in the films was investigated and the TOF-SIMS showed that the ions were homogeneously distributed throughout the ZnTiO3 host lattice which indicated a successful incorporation of the Er3+ and Yb3+ ions. The optical response of the phosphors revealed that the reflectance percentages of the ZnTiO3:Er3+, Yb3+ vary with the silicon substrate temperature due to the differences in the thickness and morphological roughness of the thin films. The ZnTiO3:Er3+, Yb3+ thin films also exhibited up-conversion emission from Er3+ electronic transitions, with violet, blue, green and red emission lines at 410, 480, 525, 545 and 660 nm from 2H9/2 → 4 I15/2, 4F7/2 → 4 I15/2, 2H11/2 → 4 I15/2, 4S3/2 → 4 I15/2 and 4F9/2 → 4 I15/2 transitions, respectively. These up-conversion emissions were enhanced by increasing the silicon substrate temperature during the deposition. ZnTiO3 host co-doped with Eu3+ and Al3+ was synthesized by solid state reaction to convert the UV photons to visible photons. Charge compensation effects of Al3+ incorporated ZnTiO3:Eu3+ as a co-dopant ion was reported in detail. The structural and morphological characterization show that the addition of Eu3+ and Al3+ does not affect the phase formation and the surface morphology of the host. The visible emission intensity of Eu3+ ions for an optimal concentration of 2 mol% under 395 nm excitation, was enhanced by incorporating Al3+. The energy level diagram showing the charge compensation mechanism was proposed for the co-doped system.<br>College of Engineering, Science and Technology