Solution based temperature of Perovskite-type oxide films and powders
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Conventional solid state reactions are diffusion limited processes that require high temperatures and long reaction times to reach completion. In this work, several solution based methods were utilized to circumvent this diffusion limited reaction and achieve product formation at lower temperatures. The solution methods studied all have the common goal of trapping the homogeneity inherent in a solution and transferring this homogeneity to the solid state, thereby creating a solid atomic mixture of reactants. These atomic mixtures can yield solid state products through {open_quotes}diffusionless{close_quotes} mechanisms. The effectiveness of atomic mixtures in solid state synthesis was tested on three classes of materials, varying in complexity. A procedure was invented for obtaining the highly water soluble salt, titanyl nitrate, TiO(NO{sub 3}){sub 2}, in crystalline form, which allowed the production of titanate materials by freeze drying. The freeze drying procedures yielded phase pure, nanocrystalline BaTiO{sub 3} and the complete SYNROC-B phase assemblage after ten minute heat treatments at 600{degrees}C and 1100{degrees}C, respectively. Two novel methods were developed for the solution based synthesis of Ba{sub 2}YCu{sub 3}O{sub 7-x} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}. Thin and thick films of Ba{sub 2}YCu{sub 3}O{sub 7-x} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} were synthesized by an atmospheric pressure, chemical vapor deposition technique. Liquid ammonia solutions of metal nitrates were atomized with a stream of N{sub 2}O and ignited with a hydrogen/oxygen torch. The resulting flame was used to coat a substrate with superconducting material. Bulk powders of Ba{sub 2}YCu{sub 3}O{sub 7-x} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} were synthesized through a novel acetate glass method. The materials prepared were characterized by XRD, TEM, SEM, TGA, DTA, magnetic susceptibility and electrical resistivity measurements.Keywords:
Nanocrystalline material
Atomic diffusion
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Barium titanate (BaTiO 3 ) powders were prepared by a polymerized complex method based on the Pechini‐type reaction route, wherein a mixed solution of citric acid (CA), ethylene glycol (EG), and barium and titanium ions, with a molar ratio of CA:EG:Ba:Ti = 10:40:1:1, was polymerized to form a transparent resin, which was used as a precursor for BaTiO 3 . Characterization of the initial precursor solution of EG, CA, and barium and titanium ions by Raman scattering and 13 C‐NMR spectroscopy indicated that barium and titanium ions were simultaneously stabilized with CA to form a barium‐titanium mixed‐metal CA complex with a stoichiometry similar to Ba:Ti:CA = 1:1:3. Raman and 13 C‐NMR spectra of the liquid mixture at various reaction stages indicated that the fundamental coordination structure of the mixed‐metal complex remained almost unchanged throughout the polymerization process. X‐ray diffractometry (XRD) measurements indicated formation of pseudo‐cubic BaTiO 3 free from BaCO 3 and TiO 2 when the barium‐titanium polymeric precursor was heat‐treated in air at 500°C for 8 h or at 600°C for 2 h. However, the Raman spectra of the same powders indicated the formation of tetragonal (rather than cubic) BaTiO 3 , with traces of high‐temperature hexagonal BaTiO 3 stabilized at room temperature. XRD of a pyrolyzed product at 500°C for 2 h revealed a simple mixture of BaTiO 3 and an intermediate phase, Ba 2 Ti 2 O 5 . CO 3 . A solid‐state reaction between BaCO 3 and TiO 2 was concluded as not being responsible for the BaTiO 3 formation; rather, BaTiO 3 formed directly by thermal decomposition of the intermediate Ba 2 Ti 2 O 5 . CO 3 phase at temperatures >500°C. In addition, by Raman scattering measurements, the intermediate Ba 2 Ti 2 O 5 . CO 3 phase was found to be unstable in ambient air, yielding BaCO 3 as one of the decomposed products.
Barium
Barium titanate
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Ex-situ post-deposition reaction processing is considered a promising alternative to in-situ physical vapor deposition techniques for coated Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} conductor development. It was reported recently, that attempts at ex-situ processing of long Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} precursor tapes resulted in an inhomogeneous growth rate over the tape length and rather poor properties for the whole sample. We performed a set of experiments in order to clarify the mechanisms for the ex-situ processing of large area films and estimate properties of long coated conductors manufactured by the ex-situ technique. It was found that rate limiting step of ex-situ growth of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} is removal of the reaction product, hydrofluoric acid, by both gas diffusion and convection in the reaction atmosphere. We report on a quantitative model that well describes the observed growth rates for films with various areas.
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The present work reports that highly c ‐axis‐oriented Tl‐Ba‐Ca‐Cu‐O superconducting films with zero‐resistance temperature up to 112 K were successfully prepared using the spray pyrolysis technique with a subsequent Tl‐diffusion treatment. The insalating Ba‐Ca‐Cu‐O precursor films (Ba:Ca:Cu = 2:2:3) were made by spray deposition of the related metal nitrate solution on a preheated (300°–400°C) MgO(001) single‐crystal substrate. The presence of the superconducting phases of the resultant films depended strongly on the types of Tl sources used. The results showed that the formation of the super conducting phases could be achieved more readily by using the bulk Tl‐Ba‐Ca‐du‐O rather than Tl 2 O 3 as a Tl source. In other words, the low Tl content in the TlBaCaCuO bulk source with a resulting low Tl‐vapor pressure is favorable for the formation of a higher T c superconducting phase. The dominant phases in the prepared films were mainly TlBa 2 Ca 2 Cu 3 O/(1223 phase) and Tl 2 Ba 2 CaCu 2 O y (2212 phase). The critical current density of a film with a nearly single‐phase(1223) structure was measured to be 1.2 × 10 4 A/cm 2 at 77 K under zero magnetic field.
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Lutetium
Thermal Stability
Hydrothermal Synthesis
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Partial pressure
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Conventional solid state reactions are diffusion limited processes that require high temperatures and long reaction times to reach completion. In this work, several solution based methods were utilized to circumvent this diffusion limited reaction and achieve product formation at lower temperatures. The solution methods studied all have the common goal of trapping the homogeneity inherent in a solution and transferring this homogeneity to the solid state, thereby creating a solid atomic mixture of reactants. These atomic mixtures can yield solid state products through diffusionless mechanisms. The effectiveness of atomic mixtures in solid state synthesis was tested on three classes of materials, varying in complexity. A procedure was invented for obtaining the highly water soluble salt, titanyl nitrate, TiO(NO3)2, in crystalline form, which allowed the production of titanate materials by freeze drying. The freeze drying procedures yielded phase pure, nanocrystalline BaTiO3 and the complete SYNROC-B phase assemblage after ten minute heat treatments at 600 C and 1,100 C, respectively. Two novel methods were developed for the solution based synthesis of Ba2YCu3O7-x and Bi2Sr2Ca2Cu3O10. Thin and thick films of Ba2YCu3O7-x and Bi2Sr2Ca2Cu3O10 were synthesized by an atmospheric pressure, chemical vapor deposition technique. Liquid ammonia solutions of metal nitrates were atomized with a stream of N2O and ignited with a hydrogen/oxygen torch. The resulting flame was used to coat a substrate with superconducting material. Bulk powders of Ba2YCu3O7-x and Bi2Sr2Ca2Cu3O10 were synthesized through a novel acetate glass method. The materials prepared were characterized by XRD, TEM, SEM, TGA, DTA, magnetic susceptibility and electrical resistivity measurements.
Nanocrystalline material
Atomic diffusion
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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Anhydrous
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Potassium hydroxide
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