First-principles prediction of oxygen octahedral rotations in perovskite-structure EuTiO3

TL;DR

This study uses first-principles calculations to predict the structural distortions and stability of EuTiO3 perovskite, revealing preferred octahedral rotation patterns and their effects on properties.

Contribution

It systematically identifies the most stable octahedral tilt patterns in EuTiO3 using first-principles methods, expanding understanding of its structural behavior.

Findings

I4/mcm, Imma, and Rar{3}c structures are energetically favored over the cubic prototype.

Strong phonon instabilities suggest a tendency for symmetry-lowering distortions.

Antiferrodistortive rotations significantly influence EuTiO3's vibrational, optical, and magnetic properties.

Abstract

We present a systematic first-principles study of the structural and vibrational properties of perovskite-structure EuTiO3. Our calculated phonon spectrum of the high-symmetry cubic structural prototype shows strong M- and R-point instabilities, indicating a tendency to symmetry-lowering structural deformations composed of rotations and tilts of the oxygen octahedra. Subsequent explicit study of 14 different octahedral tilt-patterns showed that the I4/mcm, Imma, and R\bar{3}c structures, all with antiferrodistortive rotations of the octahedra, have significantly lower total energy than the prototype Pm\bar{3}m structure. We discuss the dynamical stability of these structures, and the influence of the antiferrodistortive structural distortions on the vibrational, optical, and magnetic properties of EuTiO3, in the context of recent unexplained experimental observations.