Pressure effects on model ferroelectric BiFeO₃−PbTiO₃: Multiple phase transitions

Abstract

Pressure-dependent powder x-ray diffraction, Raman spectroscopy, and dielectric constant measurements are performed on 0. 65 BiFeO₃ − 0.35 PbTiO₃. Four structural transitions are reported in 0–34 GPa range. The transitions are observed at 0.7(1), 0.8(1), 3.4(1), and 6.1(1) GPa, where the system transformed from ambient tetragonal P 4 m m to a mixed phase of tetragonal and rhombohedral (P4mm + R3c) , followed by transition to rhombohedral R 3 c , cubic Pm 3 m and again to rhombohedral R 3 c structure, respectively. The transformation to the cubic structure coincides with the ferroelectric-paraelectric transition. Higher-pressure cubic-to-rhombohedral transition shows a slight softening of Raman modes along with an enhancement in spontaneous strain. The high-pressure rhombohedral phase shows signatures of another ferroic transition.