Lattice Distortion Upon Compression in Orthorhombic Perovskites: Review and Development of a Predictive Tool

Perovskites are one of the most important class of materials belonging to the category “minerals as advanced materials”. In fact, thousands of works every year are devoted to establish the countless properties of these compounds which were first discovered in 1839 as minerals in the Ural mountains and whose synthetic analogs find now application in many technological fields. The behavior under pressure of the orthorhombic perovskites is essentially associated to the relative compressibilities of the two polyhedra (AO12 and BO6) controlling the tilting and distortion effects. The only two possible structural answers to the compression regime are: 1) the AO12 site is more compressible than the BO6 octahedra, then volume reduction will lead to an increasing of the octahedral tilting; 2) the AO12 site is less compressible than the BO6 octahedra, then the structure will evolve by decreasing the octahedral tilting raising its symmetry towards the cubic archetype. This work was aimed to give a useful tool that relates the lattice distortion of an orthorhombic perovskite under pressure to the relative compressibilities of the two polyhedra, by comparing several high pressure studies of GdFeO3-type perovskites under high-pressure from the literature