Phase transition and phase stability in [110]-, [001]-, and [111]-oriented 0.68Pb(Mg1/3Nb2/3)O3−0.32PbTiO3 single crystal under electric field

Abstract

The phase transition and the phase stability in 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PMN-0.32PT) single crystals under different electric fields were investigated over a temperature range from −20 to 200 °C using the dielectric property. Crystals with different orientations were used in the research. First, it is found that the intermediate monoclinic or orthorhombic phases are involved in the phase transition from the rhombohedral to tetragonal phase and that the appearance and stability of the intermediate phases as well as the phase path are strongly dependent on factors, such as the history of the sample and the direction and strength of the electric field. The transition behavior from the rhombohedral to tetragonal phase for the samples during the field-heating process is much more complex than that during the field-cooling process. Second, for the ferroelectric-to-paraelectric phase transition, it is found that the dielectric-constant peak actually reflects two processes: one is the ferroelectric relaxor process and the other is the tetragonal to cubic phase transition. The electric field shifts both transitions toward high temperature at different rates, which results in a “λ-like” dielectric-constant peak in [111]-oriented samples. The results indicate that the polar regions in the ferroelectric relaxors should have a spontaneous polarization along the [111] direction. Finally, the temperature–electric field (T-E) phase diagrams for crystals under electric field along different directions. It is also found that the piezoelectric activities are strongly related to the appearance of the intermediate phases.