Effect of Ti on the stability of phases in the (1 - X)Pb(Mg _1/3Nb _2/3)O ₃-xPbTiO ₃ solid solution

Occurrence of the M_B-type monoclinic phase induced by the lattice distortion of the rhombohedral structure was evidenced by means of high-resolution x-ray powder diffraction, simplified integrate-breadth analysis and Rietveld refinement in the (1-x)- Pb(Mg_1/3Nb_2/3)O ₃-xPbTiO₃(PMN-xPT) ceramics with 15%≤x≤30%. The obvious distortion of lattice along [00h]_Cwas observed in the composition range 23%≤x≤30%, and increased with the Ti content. Rietveld refinements indicate that the M_B-type monoclinic phase exists in the composition range 23%≤x≤25%, and coexists, as a majority phase, with the M_C-type monoclinic phase for 26%≤x≤30%. The rhombohedral (R) phase is stable in the composition range of 15%≤x < 23%. The effect of Ti on the lattice distortion and phase stability in the PMN-PT solid solution is discussed based on the model of competition between rhombohedral and tetragonal polar orders.