Influence of Columbite MgNb2O6 on the Perovskite Formation and Microstructure of Pb(Mg1/3Nb2/3)O3 Ceramics

The influence of the calcination conditions of MgNb2O6 on the perovskite formation and microstructure of Pb(Mg1/3Nb2/3)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(Mg1/3Nb2/3)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(Mg1/3Nb2/3)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(Mg1/3Nb2/3)O3.