Pressure-induced structural phase transitions and phonon anomalies inReO3: Raman and first-principles study

Abstract

We report high-pressure Raman-scattering studies on single-crystal $\mathrm{Re}{\mathrm{O}}_{3}$ up to 26.9 GPa at room temperature, complemented by first-principles density functional calculations to assign the modes and to develop understanding of the subtle features of the low-pressure phase transition. The pressure $(P)$ dependence of phonon frequencies $(\ensuremath{\omega})$ reveals three phase transitions at 0.6, 3, and 12.5 GPa with characteristic splitting and changes in the slope of $\ensuremath{\omega}(P)$. Our first-principles theoretical analysis confirms the role of the rotational modes of $\mathrm{Re}{\mathrm{O}}_{6},\phantom{\rule{0.16em}{0ex}}{M}_{3}$, to the lowest pressure structural transition, and shows that the transition from the $Pm3m$ to the $Im3$ structure is a weak first-order transition, originating from the strong anharmonic coupling of the ${M}_{3}$ modes with the acoustic modes (strain).