The authors have calculated the phonon dispersion curves of barium titanate (BaTiO 3 ) in the cubic phase. A nonlinear shell model is used, in which the fourth-order anharmonic core-shell interaction of the oxygen ion is considered within a self-consistent phonon approximation. The temperature dependence of the ferroelectric soft mode is reproduced by their calculations, leading to the linear and nonlinear contributions of the O polarisability. The values of the relevant model parameters are critically analysed.
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Khatib et al. (1989) studied this question.
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