Phase transitions in the ferroelectric relaxor (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3 close to the morphotropic phase boundary

Abstract

Structural transformations of unpoled (1−x)Pb(Mg1/3Nb2/3)O3−xPbTiO3(PMN-PT) single crystals (x=0.28 and x=0.32) were analyzed by calorimetry and acoustic spectroscopy. The compositions are close to the morphotropic boundary (MPB). We find extended two-phase regions where cubic and rhombohedral (x=0.28), cubic and tetragonal, tetragonal and monoclinic phases (x=0.32) coexist during cooling and heating. The observed structural transitions in PMN-PT are first order, despite their proximity to the MPB. The predicted tricritical points, if they exist, are possibly located extremely close to the MPB.