Lattice dynamics study on cubic barium titanate based upon a modified rigid-shell model

Abstract

The rigid-shell model has been revisited in this paper for the lattice dynamics calculations in the paraelectric BaTiO₃ since a few decades ago. The conventional harmonic models of Cowley et al. and Jannot et al., have been modified by including more interatomic force constants. The force constants were adjusted to fit the calculated phonon dispersion curves to the observed data from inelastic neutron scattering studies that were available in the literature. The calculated dispersions agree satisfactorily with the experimental results. Degeneracies of the phonon branches, as required by the crystal symmetry consideration, have been correctly reproduced for the first time. The fitting parameters of our model have values whose trends are seen to have similar behavior to the previous models. Moreover, the newly employed parameters have shown interesting features related to the short-range, non-Coulombic interactions of the ions.

Key Words:

• Perovskite
• phonon
• rigid-shell model
• lattice dynamics