Stoichiometry Control and Phase Selection in Hydrothermally Derived BaxSr1–xTiO3 Powders

Ba _x Sr_{1- x} TiO₃ (BST) powders were processed at temperatures <100°C by reacting nanosized TiO₂ powders in alkaline, aqueous solutions of BaCl₂, SrCl₂, and NaOH. The effects of processing variables (NaOH concentration, time, temperature, and the ratios of barium, strontium, and titanium initially in solution) on the resultant BST powder stoichiometry and solid solubility were examined. In all cases, strontium was more readily incorporated into the BST powders than barium, and the extent varied systematically with the processing variables. BST powders that were processed in solutions with a large initial excess of barium and strontium, relative to titanium, consisted of a single-phase solid solution. In contrast, BST powders that were processed in solutions with a small initial excess of barium and strontium, relative to titanium, contained a biphasic solid solution which corresponded to separate barium-rich and strontium-rich phases.