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The formation of BaTiO3 nanoparticles by a solid-state reaction between nanocrystalline raw materials BaCO3 and TiO2 was studied as a function of temperature (400°–800°C), time (1–24 h), and titania particle size (15 and 30 nm). The reaction starts at 500°C and a high reaction rate is already observed at 600°C for the finest titania, with up to 90% conversion after 2 h. Two main reaction stages were observed at 600°–700°C. The first step is dominated by nucleation and growth of BaTiO3 at the TiO2–BaCO3 contact points and at the TiO2 surface. Surface diffusion of BaCO3 is, most likely, the prevailing mass transport mechanism responsible for the rapid formation of BaTiO3, even in the absence of a significant contribution from lattice diffusion. The second stage begins when the residual TiO2 cores are completely covered by the product phase. For longer times, the reaction can only proceed by the slower lattice diffusion, resulting in a strong decrease of the reaction rate. Single-phase BaTiO3 nanopowders with a specific surface area of 12–15 m2/g, an average particle size of 70–85 nm, a relative density of 96.5%–98.3%, and a tetragonality of 1.005 were obtained by calcination at 700°–800°C. Critical parameters in the preparation of ultrafine powders by solid-state reactions are the particle size of both raw materials, the absence of large hard agglomerates, and the homogeneity of the mixture. The use of fine raw materials and optimization of the reaction conditions make mechanical activation unnecessary. [ABSTRACT FROM AUTHOR]

Barium titanate has been prepared by solid-state reaction of nanocrystalline TiO2 (70 nm) with BaCO3 of different particle size (650, 140, and 50 nm). The results give evidence of a strong effect of the size of BaCO3 in the solid-state synthesis of barium titanate. The use of nanocrystalline BaCO3 already leads to formation of the single-phase BaTiO3 after calcination for 8 h at 800°C. The final powder consists of primary particles of ≈100 nm, has a narrow particle size distribution with d50=270 nm, and no agglomerates larger than 800 nm. For the coarser carbonate, 4 h calcination at 1000°C are required and the final powder is much coarser. Solid-state reaction of nanocrystalline BaCO3 and TiO2 represents an alternative to chemical preparation routes for the production of barium titanate ultrafine powders. [ABSTRACT FROM AUTHOR]

Barium titanate has been prepared by solid-state reaction of nanocrystalline TiO2 (70 nm) with BaCO3 of different particle size (650, 140, and 50 nm). The results give evidence of a strong effect of the size of BaCO3 in the solid-state synthesis of barium titanate. The use of nanocrystalline BaCO3 already leads to formation of the single-phase BaTiO3 after calcination for 8 h at 800°C. The final powder consists of primary particles of ≈100 nm, has a narrow particle size distribution with d50=270 nm, and no agglomerates larger than 800 nm. For the coarser carbonate, 4 h calcination at 1000°C are required and the final powder is much coarser. Solid-state reaction of nanocrystalline BaCO3 and TiO2 represents an alternative to chemical preparation routes for the production of barium titanate ultrafine powders. [ABSTRACT FROM AUTHOR]

Well-defined and stoichiometric spherical particles of BaTiO[sub 3] of narrow size distribution were produced at 82° and 92°C by precipitation from chloride solutions in a strong alkaline environment. The size of the particles can be tailored in the range from ≈10³ to 70-80 nm by increasing the barium concentration from ≈0.07 to 0.7 mol/L. The particles are composed of tight aggregates resulting from the assembly of several nanocrystals. The size of the nanocrystals decreases from 200-300 to 30-40 nm by increasing reactant concentration. At low barium concentration (≤0.07 mol/L at 82°C, ≤0.06 mol/L at 92°C), formation of BaTiO[sub 3] is strongly slowed down and nonstoichiometric, Ti-rich powders are produced. Under these conditions, the particles have the tendency to develop a dendritic-like morphology. [ABSTRACT FROM AUTHOR]

Examines the incorporation of erbium into barium titanate ceramics. Incorporation of erbium at the titanium site; Reduction of tetragonality; Fabrication of electric and electronic devices.

Atomistic simulation methods based on pair-wise interatomic potentials and energy minimization have been applied to elucidate the energetics of cation vacancies and the incorporation of 13 trivalent M3+ cations (Cr3+, Ga3+, Fe3+, Lu3+, Yb3+, Er3+, Y3+, Tb3+, Gd3+, Eu3+, Sm3+, Nd3+, La3+) in γ-Al2O3. Calculations have been carried out using Al64O96 defect spinel supercells containing eight aluminum vacancies. The lowest energy configurations correspond to a random distribution of tetrahedral and octahedral vacancies. The energy gain in comparison with exclusive tetrahedral or octahedral vacancies is rather small (0.03 and 0.09 eV/Al2O3, respectively). Unit cell volume, density, and lattice properties of optimized structures are in good agreement with the experimental values or the results of high-quality density functional theory calculations. The trends observed for the solution energy of the M2O3 oxides in the supercell with minimum energy indicate the preferential incorporation of the foreign ions at the tetrahedral site and an increase of the solubility of M2O3 in the defect spinel in comparison with α-Al2O3. Configurations with the lowest energy have negative solution energies and, consequently, incorporation of trivalent ions can improve the thermodynamic stability of γ-Al2O3 in comparison with α-Al2O3 and increase the γ→α transition temperature. [ABSTRACT FROM AUTHOR]