Ferroelectricity in [111]-oriented epitaxially strained SrTiO3 from first principles

We use first-principles density-functional theory calculations to investigate the effect of biaxial strain in the low-temperature structural and ferroelectric properties of [111]-oriented SrTiO3. We find that [111] biaxial strain, achievable by coherent epitaxial growth along the [111] direction, induces structural distortions in SrTiO3 that are not present in either bulk or [001]-oriented SrTiO3. Under [111] biaxial strain, SrTiO3 displays ferroelectricity at tensile strain, and paraelectricity at compressive strain. We compute the phonon spectrum and macroscopic polarization of SrTiO3 as a function of [111] biaxial strain, and relate our results to the predictions of the free-energy phenomenological model of Pertsev, Tagantsev, and Setter [Phys. Rev. B 61, 825 (2000)PRBMDO0163-182910.1103/PhysRevB.61.R825; Phys. Rev. B 65, 219901 (2002)10.1103/PhysRevB.65.219901].