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.