Thermal decomposition of ktn gel and formation of perovskite structure KTN

Abstract

This paper reported the thermal decomposition process of KTN Gel and the formation process perovskite structure KTN. Two pyrochlore phases formed in the heat treatment process, one was potassium-deficient pyrochlore phase K3Ta5O14 • 5H2O, another was potassium-rich pyrochlore phase K3Nb2O6(O, OH) • nH2O. The transformation of two pyrochlore phases and perovskite structure KTN were influenced by the potassium content and the heat treatment temperature. The pyrochlore phases readily formed at a lower temperature, at a higher temperature (680°C-750°C), the pyrochlore phases transformed to the pure perovskite structure KTN, but the perovskite structure KTN would decompose to form potassium-deficient pyrochlore phases Ta2O5 • n(KTaO3)(n=2, 3, 4) with the temperature gone np(>950°C). When potassium was excess in the starting materials, the transformation temperature of the pyrochlore phases to perovskite phase was higher, even at 1200°C. When K/Ta, Nb < 1 in the starting materials, the pure perovskite structure KTN could not be obtained