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Ab Initio Calculations of the Effect of Non-Rigid Ions on the Statics and Dynamics of Oxides

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1985

Year

Abstract

The potential induced breathing of oxygen ions in a crystal, which plays a major role in explaining the violation of the Cauchy relations and the splitting of the longitudinal and transverse optic frequencies in alkaline earth oxides, is analyzed for BaTiO 3 in the perovskite structure and the distorted structure corresponding to the tetragonal phase. The results indicate that nonspherical ions are required to describe the ferroelectric transition.