Pressure effects on model ferroelectricBiFeO3−PbTiO3: Multiple phase transitions

Abstract

Pressure-dependent powder x-ray diffraction, Raman spectroscopy, and dielectric constant measurements are performed on 0.$65{\mathrm{BiFeO}}_{3}\text{\ensuremath{-}}0.35{\mathrm{PbTiO}}_{3}$. 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 $P4mm$ to a mixed phase of tetragonal and rhombohedral $(P4mm+R3c)$, followed by transition to rhombohedral $R3c$, cubic Pm$3m$ and again to rhombohedral $R3c$ 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.