Influence of columbite MgNb 2 O 6 on the perovskite formation and microstructure of Pb (Mg 1/3 Nb 2/3 )O 3 ceramics

The influence of the calcination conditions of MgNb 2 O 6 on the perovskite formation and microstructure of Pb (Mg 1/3 Nb 2/3 )O 3 prepared by the columbite process was investigated. The purity of MgNb 2 O 6 was found to significantly affect the formation process of perovskite phase. Lower purity of MgNb 2 O 6 led to retard the formation of perovskite phase. Calcination at temperatures above 800¢XC resulted in the complete formation of MgNb 2 O 6 . Pure MgNb 2 O 6 efficiently reacted with PbO, and accelerated the formation of perovskite phase. On the condition of without adding excess MgO or PbO, heating 1000¢XC-calcined MgNb 2 O 6 with PbO at 800¢XC for 2h resulted in monophasic Pb (Mg 1/3 Nb 2/3 )O 3 having submicron size. On the other hand, when MgNb 2 O 6 was prepared by 1200¢XC-calcination, the unfavorable grain-growth of MgNb 2 O 6 caused the decrease in the reactivity between MgNb 2 O 6 and PbO. The over-calcination of MgNb 2 O 6 also led the grain size of Pb (Mg 1/3 Nb 2/3 )O 3 to greatly increase to be around 2.5 £gm. Consequently, the calcination conditions of MgNb 2 O 6 markedly affected the reaction kinetics and grain size of Pb (Mg 1/3 Nb 2/3 )O 3 .