Perovskite phase formation in the PbMg_1/3Nb_2/3 O₃-PbZrO₃-PbTiO₃ system by the columbite route

Abstract

The reaction mechanism of PbMg_1/3Nb_2/3O₃-PbZrO₃-PbTiO₃ (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 °C. The effects of heating and cooling rate during the calcination of 3PbO +MgNb₂O₆+PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-0.1 PZTsolid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 °C for 2 H. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps: (i) decomposition of columbite (MgNb₂O₆) by reacting with PbO at 350 to 600 °C (ii) the formation of a B-site-deficient pyrochlore phase Pb₂Nb_1.33Mg_0.17O_5.50 at close to 650 °C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb₂Nb_1.33Mg_0.17O_5.50 pyrochlore phase with MgO and PZT above 650 °C.