Effects of dopants on the microstructure and phase-purity control in PMN-PT ceramics

The effects of Pb2+, Ba2+, La3+, Y3+ and Gd3+ dopants on the densification and microstructure evolution of PMN-PT ceramics are investigated. The ceramics were reactively-sintered between 850 and 1250 °C in oxygen atmosphere. After sintering, all ceramics reached a relative density greater than 98%. XRD and SEM results revealed that lanthanum doping produces pure perovskite phase with unimodal rounded grains whereas other dopants yield microstructures with faceted grains due to the liquid phase formed in the intermediate stage. The mechanism for the observed differences in phase and morphology is also explored. The slower densification rate of La-doped samples helps maintain an open porosity network and favors the outgassing of the initial excess of PbO. The delayed densification contributes to the formation of pure perovskite at a temperature of 850 °C. Preferential A-site occupancy of La3+ lowers the oxygen vacancy concentration which suppresses grain growth.