Electronic and Polar Properties of Vanadate Compounds Stabilized by Epitaxial Strain

Recent experimental and computational studies have demonstrated pressure and epitaxial stabilization of polar PbVO3 phases with perovskite-derivative crystal structures. In this study, we demonstrate, by density functional theory (DFT) calculations, the stability of similar perovskite-derivative structures in the KVO3 and NaVO3 systems when subjected to compressive biaxial strain. The electronic structure and polar properties of these compounds are computed as a function of biaxial strain, and the results are compared to those obtained for experimentally observed PbVO3 structures. It is demonstrated that the substitution of Pb with monovalent K or Na cations increases the strength of the vanadyl bond due to the removal of the spatially extended Pb 6p states. Both KVO3 and NaVO3 exhibit epitaxially stabilized perovskite-derivative phases having large polarizations and only small total energy increases relative to their unstrained bulk structures. The calculated epitaxial phase diagram for KVO3 predicts a strain-energy driving force for a phase separation from −4% to 1.5% misfit strain into a polar Cm phase, having square-pyramidal coordination of the B-site, and a paraelectric Pbcm phase, having tetrahedral coordination of the B-site. The results show that strain-stabilized polar vanadate compounds may occur for other compositions in addition to PbVO3 and that changes in the A-site species can be used to tune bonding, structure, and functional properties in these systems.