Strain-induced ferroelectricity in CaTiO\(_3\) from first principles

Abstract

First principles calculations are used to investigate the effects of epitaxial strain on the structure of the perovskite oxide CaTiO\(_3\), with particular focus on the stabilization of a ferroelectric phase related to a polar instability hidden in the orthorhombic equilibrium bulk \(Pbnm\) structure but found in previous first-principles studies of the ideal cubic perovskite high-symmetry reference structure. At 1.5% strain, we find an epitaxial orientation transition between the \(ab\)-\(ePbnm\) phase, favored for compressive strains, and the \(c\)-\(ePbnm\) phase. For larger tensile strains, a polar instability develops in the \(c\)-\(ePbnm\) phase and an epitaxial-strain-induced ferroelectric phase is obtained with polarization along a \(<\)110\(>\) direction with respect to the primitive perovskite lattice vectors of the square substrate.