Locked octahedral tilting in orthorhombic perovskites: At the boundary of the general rule predicting phase transitions

Abstract

Mainly ruled by oxygen octahedral rotations, perovskite oxides can exhibit zone boundary transitions (ZBTs) either with $d{T}_{c}/dP>\phantom{\rule{0.16em}{0ex}}0$ or $d{T}_{c}/dP<\phantom{\rule{0.16em}{0ex}}0$. Synchrotron structural investigations at high pressure conditions place $\mathrm{YA}{\mathrm{l}}_{0.25}\mathrm{C}{\mathrm{r}}_{0.75}{\mathrm{O}}_{3}$ orthorhombic perovskite at the boundary of ZBTs. The absence of changes in the octahedral tilting and a volume reduction with pressure exclusively controlled by an isotropic polyhedral compression set $\mathrm{YA}{\mathrm{l}}_{0.25}\mathrm{C}{\mathrm{r}}_{0.75}{\mathrm{O}}_{3}$ as the first finding of a possible asymptote at the Clapeyron relation for predicting ZBTs in perovskites. Furthermore, the discovery of a ``locked-tilt perovskite'' can pave the way to a new class of functional materials.