The phase formation and transition mechanism of lead magnesium niobate-lead titanate [(1-x)Pb(Mg1/3Nb2/3)O-3-xPbTiO(3), PMN-PT, 0 less than or equal to x less than or equal to 1] were investigated by thermal analysis and XRD. The effect of process parameters such as x values, synthesis temperatures, and excess PbO on phase transitions were studied in terms of the diffraction peak splitting. The results show that the perovskite phases undergo the transitions pseudocubic --> rhombohedral --> coexistence of rhombohedral and tetragonal --> tetragonal in the x value range 0-1. At the composition of morphotropic phase boundary, preferential formation of the PMN-PT tetragonal phase was observed and discussed at elevated synthesis temperatures or with enhanced excess PbO. (C) 2003 Elsevier B.V. All rights reserved.