Influence of Columbite MgNb₂O₆ on the Perovskite Formation and Microstructure of Pb(Mg_1/3Nb_2/3)O₃ Ceramics

Abstract

The influence of the calcination conditions of MgNb₂O₆ on the perovskite formation and microstructure of Pb(Mg_1/3Nb_2/3)O₃ prepared by the columbite process was investigated. The purity of MgNb₂O₆ was found to significantly affect the formation process of perovskite phase. Lower purity of MgNb₂O₆ led to retard the formation of perovskite phase. Calcination at temperatures above 800°C resulted in the complete formation of MgNb₂O₆. Pure MgNb₂O₆ efficiently reacted with PbO, and accelerated the formation of perovskite phase. On the condition of without adding excess MgO or PbO, heating 1000°C-calcined MgNb₂O₆ with PbO at 800°C for 2h resulted in monophasic Pb(Mg_1/3Nb_2/3)O₃ having submicron size. On the other hand, when MgNb₂O₆ was prepared by 1200°C-calcination, the unfavorable grain-growth of MgNb₂O₆ caused the decrease in the reactivity between MgNb₂O₆ and PbO. The over-calcination of MgNb₂O₆ also led the grain size of Pb(Mg_1/3Nb_2/3)O₃ to greatly increase to be around 2.5μm. Consequently, the calcination conditions of MgNb₂O₆ markedly affected the reaction kinetics and grain size of Pb(Mg_1/3Nb_2/3)O₃.