Birefringence imaging measurements on the phase diagram of Pb(Mg1/3Nb2/3)O₃–PbTiO₃

The phase diagram of (PbMg 1/3 Nb 2/3 O 3 ) 1− x –(PbTiO 3 ) x (PMN–PT) has been determined to high accuracy over the whole compositional range using birefringence imaging. A steep change has been detected in the thermal hysteresis of phase transitions in the morphotropic phase boundary region at x = 0.295 at the boundary between relaxor and non-relaxor phases. At the same composition at a temperature about 30 °C below T c a monoclinic phase appears. The phase transition between non-relaxor and the monoclinic phase is characterized by a pronounced thermal hysteresis and a large jump in birefringence, showing that this is of first order. A significant change in slope for the compositional dependence of T c has been found for , suggesting a boundary between the tetragonal phase and a phase of lower symmetry. The temperature dependence of the birefringence has been measured for a number of different compositions in the range 0.3< x <1, in which it is found that the birefringence of the monoclinic phase is much higher than that seen in the other phases for x <0.5.