A systematic kinetic investigation on the chemical synthesis of BaTiO 3 particles from aqueous solutions of BaCl 2 and TiCl 4 at T < 100°C and at pH 14 has been performed. Initially, a viscous suspension of a Ti-rich gel phase is obtained at room temperature. Later, formation of BaTiO 3 is induced by heating above 70°C and the gel phase is gradually converted to the crystalline perovskite. The isothermal formation kinetics of BaTiO 3 and the evolution of crystal size and particle size during the course of reaction are significantly influenced by temperature, concentration, and barium-to-titanium ratio of the solution. The early stages of reaction (yield < 1%) are dominated by primary nucleation, and slow formation of single nanocrystals of BaTiO 3 was observed by HRTEM. At a later stage, formation of polycrystalline particles occurs by secondary nucleation of BaTiO 3 on the surface of already existing crystals. During this stage, the reaction rate increases by 1 order of magnitude. When the yield exceeds 50%, nucleation becomes less important and the reaction is dominated by growth. Final particles have a diameter in the range 0.3-1.6 µm, depending on the processing parameters.
The incorporation of Er3+ into BaTiO3 ceramics was investigated on samples containing 0.25, 0.5, 1, 2, 8, and 10 at.% of dopant, after sintering at 1350–1550°C in air. For Er3+ concentrations ≤1 at.%, dense and large‐grained ceramics with low room‐temperature resistivity (102–103Ω·cm) were obtained. The observed properties are largely independent of stoichiometry. Simultaneous substitution of Er3+ at both cation sites, with higher preference for the Ba site, is proposed. The behavior of heavily doped ceramics depends on stoichiometry. When Ba/Ti < 1, the electrical properties change from slightly semiconducting to insulating as Er concentration increases from 2 to 8 at.%. The ceramics have tetragonal perovskite structure and contain a large amount of Er2Ti2O7 pyrochlore phase. On the other hand, when Ba/Ti > 1, the ceramics are insulating, fine‐grained, and single phase. In this case, incorporation of Er3+ predominantly occurs at the Ti site, with oxygen vacancy compensation. Incorporation is accompanied by a significant reduction of tetragonality and by expansion of the unit cell. The different results indicate that Er3+ solubility at the Ba site does not exceed 1 at.%, whereas solubility at the Ti site is at least 10 at.%. However, the incorporation of Er3+ and the resulting properties are also strongly affected by sintering conditions.
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