Naihua Miao, Nicholas C Bristowe, Bin Xu, Matthieu Verstraete, Philippe Ghosez
By means of first-principles calculations, the structural, electronic, mechanical and dynamical properties of SrRuO3 are investigated. The full phonon dispersion curves of the high-temperature cubic phase of SrRuO3 are reported, highlighting strong antiferrodistortive instabilities extending along the line from the R to the M points of the Brillouin zone. We describe how cubic SrRuO3 can be turned into its Pnma ground state by introducing several rotations of the RuO6 octahedra associated with unstable antiferrodistortive modes. The energetics of different intermediate phases are discussed, pointing out that the coupling of oxygen-rotation modes with anti-polar Sr motions plays a key role in stabilizing the Pnma phase with respect to alternative rotation patterns, a feature likely shared by other orthorhombic ABO3 compounds. The phonon modes, the mechanical properties and heat capacity of the Pnma phase are also reported and compared with available experimental data.
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http://arxiv.org/abs/1307.0315
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