Structural transition in unpoled (1 − x)PMN–xPT ceramics near the morphotropic boundary

The phase relation and the structural transition in (1 − x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 ceramics for 0.28 ≤ x ≤ 0.4 were investigated by high resolution X-ray powder diffraction (HR-XRD), temperature-dependent X-ray powder diffraction (T-XRD) and dielectric analysis. Unexpected broad and frequency dispersive dielectric anomalies were observed, just below the tetragonal (T)–cubic (C) transition dielectric peaks in temperature dependent dielectric permittivity in the unpoled ceramics for x = 0.32 and 0.34. Structural analysis revealed that the monoclinic (MB) and tetragonal (T) structures coexisted in the composition range 0.32 ≤ x ≤ 0.36 at room temperature and in a wide temperature range for x = 0.32 and 0.34, however, in a non-equilibrium state. The sluggish MB–T transition is closely related to the dielectric anomalies. The metastable ferroelectric phase diagram near MPB was re-constructed based on XRD and dielectric analysis. The phase transition procedure was discussed.