Microwave-hydrothermal synthesis of tetragonal BaTiO3 under various conditions

Tetragonal BaTiO3 powders were synthesized by microwave-hydrothermal (MH) method. The effects of reaction time, reaction temperature, and reactant composition on the MH synthesis were investigated. Typical experiments were performed at 240 °C, a temperature above 200 °C in MH processing was not reported by previous workers, and used hydrous titanium oxide and Ba(OH)2 as precursors, in the absence of chloride ions and alkali metal ions to avoid contaminations. In MH process, the formation of tetragonal BaTiO3 was strongly enhanced. Tetragonal BaTiO3 formed in only 3 h and approached full tetragonality (c/a = 1.010) when aged for 20 h. At lower temperature of 220 °C, the rate of the formation of tetragonal BaTiO3 and the growth of particles slowed down, substantially. It was found that the excess Ba2+ in hydrothermal solution played an important role on promoting the formation of tetragonal BaTiO3. A few conventional hydrothermal (CH) experiments were carried out for comparison with the MH experiments.