Anisotropic thermal expansion and phase transitions in Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals

The thermal expansion and phase transitions of [0 0 1], [1 1 1], and [112¯] oriented unpoled and poled 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) single crystals were investigated by a dilatometer technique. The temperature dependence of thermal strain and thermal expansion coefficient for all three orientations showed nonlinearity and large anomalies, which related with polar regions and phase transitions. Unpoled crystals exhibited similar feature in thermal expansion. However, [0 0 1] poled crystal showed an intermediate monoclinic (M) state between rhombohedral (R) and tetragonal (T) ferroelectric states. Negative thermal expansion along [1 1 1] direction while a positive thermal expansion along [112¯] direction were observed over a wide temperature range when poled along [1 1 1] direction. The results reveal that the lattice thermal expansion and phase transitions in the crystals are anisotropic and strongly dependent upon temperature and electrical history.