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Perovskite Phase (perovskite + phase)
Selected AbstractsCrystal growth features and properties of layered rare earth and barium cobaltatesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005G. L. Bychkov Abstract High quality single crystals of LnBaCo2O5+, (0 < , < 1) (Ln = Pr, Eu, Gd, Tb, Dy) with rectangular shape and average dimensions 5 mm × 5 mm × 1 mm were grown for the first time from overstoichiometric flux melt. The data on the primary crystallization field of most cobaltate phases, which appear in parts of corresponding Gibbs triangles in the range 1373 , 1523 K are discussed. Bulk single crystals of new phases HoBaCo4O7 up to 300 mm3, YBaCo4O7 and TbBaCo4O7 up to 10 mm3 in volume were grown first. A solution of these compounds structure has been found in the space group P63mc. For the Ln = Pr, Gd, Sm, Tb, Dy, Ho based systems under the liquidus line there are several other new cobaltate phases of both perovskite, and hexagonal crystal structure. Stability of the double perovskite phase and temperature of the antiferromagnetic , ferromagnetic phase transition in relation to the radius of rare earth ions are compared. The data on the exact analysis of chemical composition, including EDX and iodometric titration, as well as results on magnetic susceptibility of EuBaCo1- xAlxO5+, (0 < x < 0.3) are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of Cation Ordering in Ba(Yb1/2Ta1/2)O3 by X-Ray Diffraction and Raman SpectroscopyINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2008Dibyaranjan Rout The complex perovskite Ba(Yb1/2Ta1/2)O3 has been prepared by the two-stage solid-state reaction method. Rietveld' refinement analysis indicates cubic perovskite phase with space group . The 1:1 cation ordering at the B-site is revealed by the presence of (111) superlattice reflection in the X-ray diffraction pattern and further evidenced by the presence of A1g and F2g vibrational modes in the Raman spectra. The dielectric constant is measured to be 29.1, the product of quality factor and resonant frequency (Q×f) is found to be 32,000 GHz and the temperature coefficient of resonant frequency (,f) is 135 (ppm/°C) in the temperature range 30,70°C. [source] Processing Conditions and Aging Effect on the Morphology of PZT Electrospun Nanofibers, and Dielectric Properties of the Resulting 3,3 PZT/Polymer CompositeJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Ebru Mensur Alkoy Lead zirconate titanate (PZT) nanofibers are obtained by electrospinning a sol,gel based solution and polyvinyl pyrrolidone (PVP) polymer, and by subsequent sintering of the electrospun precursor fibers. The average diameter of the precursor PZT/PVP green fibers has increased with the aging of the precursor solution along with an increase in the viscosity. Bead-free uniform green PZT/PVP fibers were collected at about an ,230 nm average fiber diameter using a 28 wt% PVP ratio solution with a viscosity of 290 mPa. Shrinkage of 40% was recorded on the fiber diameter after sintering. The X-ray diffraction pattern of the annealed PZT fibers exhibits no preferred orientation and a perovskite phase. Preparation of 3,3 nanocomposites by the infusion of polyvinylester into the nanofiber mat facilitates successful handling of the fragile mats and enables measurements of the dielectric properties. The dielectric constant of the PZT/polyvinylester nanocomposite of about 10% fiber volume fraction was found to be fairly stable and vary from 72 to 62 within the measurement range. The dielectric loss of the composite is below 0.08 at low frequencies and reaches a stable value of 0.04 for most of the measured frequencies. [source] Sintering Behavior and Conductivity Study of Yttrium-Doped BaCeO3,BaZrO3 Solid Solutions Using ZnO AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009He Wang The effect of ZnO on the crystal structure, sintering behavior, and electrical conductivity of yttrium-doped BaCeO3,BaZrO3 was investigated by unfixing or fixing the yttrium content noted as BaCe0.5Zr0.3Y0.2,xZnxO2.9,0.5x and BaCe0.5Zr0.3Y0.2O2.9+yZnO, respectively. Studies on the two series revealed that BaO·ZnO eutectic, rather than ZnO, was responsible for the sintering densification. For BaCe0.5Zr0.3Y0.2,xZnxO2.9,0.5x, the evaporation of ZnO·BaO eutectic was observed after sintering at 1300°C for 10 h, and few impurities were detected by XRD with x<0.20. For BaCe0.5Zr0.3Y0.2O2.9+yZnO, the concomitant loss of BaO with ZnO caused A-site deficiency and led to impurities of Y2O3 for y=0.08 and 0.14, and Y2BaZnO5 for y=0.20 during the sintering. For both series, ZnO enhanced the relative density, which was above 97% with x or y varying from 0.02 to 0.08. Energy-dispersive X-ray spectroscopy analysis revealed that ZnO hardly entered the perovskite phase. The conductivity study also suggested that ZnO did not serve as a dopant and that yttrium content was essential for sustaining a high ionic conduction. Excessive ZnO was especially detrimental to the grain boundary conduction and thus lowered the total electrical conduction. The optimized composition of BaCe0.5Zr0.3Y0.2O2.9+0.04ZnO has been obtained, with both a high relative density (,98.5%) and a high electrical conductivity (1.35 × 10,2 S/cm at 600°C). [source] Microwave Dielectric Properties of A-Site Modified Ba(Co0.7Zn0.3)1/3Nb2/3O3 by La3+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Jian Jiang Bian The sintering behavior, ordering state, and microwave dielectric properties of Ba1,xLa2x/3(Zn0.3Co0.7)1/3Nb2/3O3 Ceramics (0,x,0.06) were investigated in this paper. The X-ray diffraction (XRD) results show that all samples exhibit a single perovskite phase except for the sample with x,0.03. The sinterability is slightly improved by La doping. The long range order (LRO) degree on B-site is greatly increased with the increase of x value up to x=0.015 and then slightly decreased with the further increase of x due to the increasing amount of second phases. The dielectric constant at microwave frequency decreases slightly with the increase of x when x<0.015 and increases slightly with further increasing x for the samples sintered at 1375°C/10 h. The Q×f value increases with x up to x=0.015 and then decreases with further increase of x, which is consistent with the variation trend of LRO degree. The ,f value decreases slightly with the increase of x up to 0.006, then increases greatly with the further increase of x. An optimized dielectric properties of ,r=34, Q×f=63 159, GHz and ,f=5.21 ppm/°C were obtained for the x=0.01 sample sintered at 1425°C/10 h. [source] Phase Composition and Vaporization Study of LaGa1,xAlxO3, 0 ,x, 1, and La0.9Sr0.1Ga0.8,xAlxMg0.2O2.85, x= 0.1, 0.2, 0.3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2003Aleksandra Matraszek The vaporization of the LaGa1,xAlxO3 solid solution, 0 ,x, 1, of the perovskite structure, was investigated using Knudsen effusion mass spectrometry in the temperature range of 1623,1928 K. The partial pressures of the gaseous species O2, Ga, GaO, Ga2O, and LaO were determined for the samples investigated. The equilibrium partial pressures were used for the computation of thermodynamic activities of Ga2O3 and La2O3 at 1800 K. Thermodynamic activities of Al2O3 were obtained using Gibbs,Duhem integration. Gibbs energies of formation of the solid-solution LaGa1,xAlxO3 resulted from the thermodynamic activities of the oxide components. Samples of the chemical composition La0.9Sr0.1Ga0.8,xAlxMg0.2O2.85, x= 0.1, 0.2, 0.3, were of practical importance in solid oxide fuel cell (SOFC) technology and also were investigated. The influence of the aluminum concentration in the perovskite phase on the thermodynamic activity and volatility of Ga2O3 is presented and implications for the potential use of this material in SOFC technology are discussed. [source] Effect of Lead Content on the Structure and Electrical Properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001Huiqing Fan The effects of lead content on the structure and electrical properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 ceramics were investigated. Specimens with various lead concentrations were prepared by the conventional oxide-mixing method. When the lead concentration was slightly less than the stoichiometric amount, a large amount of pyrochlore phase was formed along with the perovskite phase. On the other hand, excessive amounts of lead led to the formation of PbO on the surface of the specimen. These second phases were seriously detrimental to electromechanical properties. The highest piezoelectric properties were observed when an excess of 1 mol% lead was added. By optimizing the specimen composition, excellent piezoelectric and dielectric properties (kp= 0.7, d33= 490 pC/N, and ,m= 15000) were obtained. [source] Mechanical Activation-Assisted Synthesis of Pb(Fe2/3W1/3)O3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2000Seok Khim Ang Perovskite Pb(Fe2/3W1/3)O3 (PFW) was prepared via a mechanical activation-assisted synthesis route from mixed oxides of PbO, Fe2O3, and WO3. The mechanically activated oxide mixture, which exhibited a specific area of >10 m2/g, underwent phase conversion from nanocrystalline lead tungstate (PbWO4) and pyrochlore (Pb2FeWO6.5) phases on sintering to yield perovskite PFW, although the formation of perovskite phase was not triggered by mechanical activation. When heated to 700°C, >98% perovskite phase was formed in the mechanically activated oxide mixture. The perovskite phase was sintered to a density of ,99% of theoretical density at 870°C for 2 h. The sintered PFW exhibited a dielectric constant of 9800 at 10 kHz, which was ,30% higher than that of the PFW derived from the oxide mixture that was not subjected to mechanical activation. [source] Lead-free piezoelectric (Na0.5Bi0.5)0.94TiO3,Ba0.06TiO3 nanofiber by electrospinningPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 9 2009Y. Q. Chen Abstract Lead-free (Na0.5Bi0.5)0.94TiO3,Ba0.06TiO3 (NBT-BT6) nanofibers were synthesized by the sol,gel process and electrospinning, and a butterfly-shaped piezoelectric response was measured by scanning force microscopy. NBT-BT6 nanofibers with perovskite phase were formed, after being cleaned at 700 °C for 1 hour, and the diameters are in the range of 150 nm to 300 nm. The average value of the effective piezoelectric coefficient d33 is 102 pm/V. The high piezoelectricity may be attributed to the easiness for the electric field to tilt the polar vector of the domain and to the increase of the possible spontaneous polarization direction. There is a potential for the application of NBT-BT6 nanofibers in nanoscale piezoelectric devices. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of the magnetic disaccommodation in La doped YIGPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2005C. Torres Abstract The relaxation of the initial magnetic permeability of La doped yttrium iron garnet (YIG) samples with nominal composition Y3,xLaxFe5O12 (0< x <0.6) is analysed in this work. The results show a very different behaviour depending on the sintering atmosphere used for the fabrication of the samples. Concretely, for the samples sintered in air, it just have been detected the usual relaxation peak found in YIG at 130 K. However, a new relaxation peak appears around room temperature for the samples sintered in CO2 atmosphere when the La content is at least of 0.3. These results have been interpreted in terms of the formation of a secondary perovskite phase when the La solubility limit is reached. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A novel route to perovskite lead zirconate titanate from glycolate precursors via the sol,gel processAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2008N. Tangboriboon Abstract A perovskite lead zirconate titanate was synthesized by the sol-gel process, using lead glycolate, sodium tris(glycozirconate) and titanium glycolate as the starting precursors. For the mole ratio Pb:Zr:Ti of 1:0.5:0.5 [Pb(Zr0.5Ti0.5)O3], TGA-DSC thermal analysis indicated that the percentage of ceramic yield was 55.8, close to the calculated chemical composition value of 49.5. The exothermic peak occurred at 268 °C below the theoretical Curie temperature of 400 °C. The pyrolysis of Pb(Zr0.5Ti0.5)O3 of the perovskite phase was investigated in terms of calcination temperature and time. The structure obtained was of the tetragonal form when calcined at temperatures below 400 °C; it transformed to the tetragonal and the cubic forms of the perovskite phase on calcination above the Curie temperature, as verified by X-ray data. The lead zirconate titanate synthesized and calcined at 400 °C for 1 h had the highest dielectric constant, the highest electrical conductivity and the dielectric loss tangent of 10 190, 0.803 × 10,3 (,.m),1 and 1.513 at 1000 Hz, respectively. The lead zirconate titanate powder synthesized has potential applications as an electronic material. Copyright © 2008 John Wiley & Sons, Ltd. [source] A novel route to perovskite lead titanate from lead and titanium glycolates via the sol,gel processAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 12 2006N. Tangboriboon Abstract Pure perovskite lead titanate powder (PbTiO3) is successfully produced via the sol,gel process using lead and titanium glycolates as starting precursors and has been synthesized by the oxide one spot synthesis process. The obtained lead titanate is of the tetragonal form of the perovskite phase, with high purity and nearly zero moisture content. From high-resolution mass spectra, the XRD technique, Raman-FTIR and TGA-DTA analysis, the lead,titanium glycolates undergo sol,gel transition through the formation of PbOTi bonds. From the SEM micrographs, the PbTiO3 particle shape transforms from an agglomerate sphere to a needle and fiber-like shapes as the calcination temperature is varied above Tc. The corresponding molecular structural transformation, from the tetragonal form to the cubic form, occurs at 430 °C. The lead titanate powder calcined at 300 °C for 3 h has the highest dielectric constant and electrical conductivity values, namely 17470 and 1.83 × 10,3, respectively. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hydrothermal Synthesis and Spark Plasma Sintering of (K, Na)NbO3 Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Nan Liu A facile hydrothermal route was adopted for synthesis of lead-free piezoceramics (K, Na)NbO3 powders. The influences of temperature and KOH/NaOH concentration on the resultant powders were investigated. Although two similar perovskite phases appeared when K/Na ratio tended toward 1:1, the two-phase coexistence tendency was weakened by increasing hydrothermal reaction temperature, and consequently only one phase could be obtained after spark plasma sintering. Reasonably good ferroelectric and piezoelectric properties were obtained for the samples after postannealing, whose piezoelectric constant (d33) reached 135 pC/N. The optimal remnant polarization (Pr) and mechanical quality factor (Qm) were 26.2 ,C/cm2 and 164, respectively, which were both twice as much as those of the samples using powders prepared from solid-state reaction. [source] Low-Temperature Fabrication of Oxide Composites for Solid-Oxide Fuel CellsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004Hongpeng He Composites of yttria-stabilized zirconia (YSZ) with Sr-doped LaCrO3 (LSC) and Sr-doped LaMnO3 (LSM) were prepared by impregnation of a porous YSZ matrix with aqueous solutions of the appropriate metal salts, followed by sintering to various temperatures. XRD measurements showed that perovskite phases formed after sintering at 1073 K, a temperature well below that at which solid-state reactions with YSZ occur. The conductivities of the LSC,YSZ and LSM,YSZ composites prepared in this way were maximized at a sintering temperature of 1373 K for LSC,YSZ and 1523 K for LSM,YSZ, although reasonable conductivities were achieved at much lower temperatures. The conductivities of the two composites increased much more rapidly with the content of the conductive oxide than has been found with conventional composites formed by mixing and sintering the oxide powders. The implications for using this approach to develop novel electrodes for SOFC applications are discussed. [source] | |||||||||||||