Melting of dxy Orbital Ordering Accompanied by Suppression of Giant Tetragonal Distortion and Insulator-to-Metal Transition in Cr-Substituted PbVO3

PbVO3 features giant tetragonal distortion (c/a = 1.23) and spontaneous polarization (Ps = 101 μC/cm2) originating from the ordering of dxy orbital of V4+ with single d electrons. A dedicated study of Cr-substituted PbVO3 prepared by high-pressure synthesis afforded a well-defined variation in c/a ratio. Ensuing changes in atomic structure were correlated to ferroelastic domain switching and a temperature-induced structural transition to a cubic phase accompanied with an insulator-to-metal transition and a negative thermal expansion.