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

Mainly ruled by oxygen octahedral rotations, perovskite oxides can exhibit zone boundary transitions (ZBTs) either with dTc/dP>0 or dTc/dP<0. Synchrotron structural investigations at high pressure conditions place YAl0.25Cr0.75O3 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 YAl0.25Cr0.75O3 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.