Hydrothermal synthesis of perovskite and pyrochlore powders of potassium tantalate

Potassium tantalate powders were hydrothermally synthesized at 100 to 200 degreesC in 4 to 15 M aqueous KOH solutions. A defect pyrochlore, KTa2O5(OH) . nH(2)O (n approximate to 1.4), was obtained at 4 M KOH, but at 7-12 M KOH, this pyrochlore was gradually replaced by a defect perovskite as the stable phase. At 15 M KOH, there was, no intermediate pyrochlore only a defect perovskite, K0.85Ta0.92O2.43(OH)(0.57) . 0.15H(2)O. Synthesis at higher KOH concentrations led to greater incorporation of protons in the perovskite structures. The potassium vacancies required for charge compensation of incorporated protons could accommodate water molecules in the perovskite structure.