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Ab initio phonon dispersion curves and interatomic force constants of barium titanate

Ph. Ghosez·X. Gonze·J. -P. Michenaud
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Abstract

The phonon dispersion curves of cubic BaTiO_3 have been computed within a first-principles approach and the results compared to the experimental data. The curves obtained are very similar to those reported for KNbO_3 by Yu and Krakauer [Phys. Rev. Lett. 74, 4067 (1995)]. They reveal that correlated atomic displacements along <100> chains are at the origin of the ferroelectric instability. A simplified model illustrates that spontaneous collective displacements will occur when a dozen of aligned atoms are coupled. The longitudinal interatomic force constant between nearest neighbour Ti and O atoms is relatively weak in comparison to that between Ti atoms in adjacent cells. The small coupling between Ti and O displacements seems however necessary to reproduce a ferroelectric instability.

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Ph. Ghosez, X. Gonze, J. -P. Michenaud. 1997-06-30. Ab initio phonon dispersion curves and interatomic force constants of barium titanate. https://arxiv.org/abs/cond-mat/9706294

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