Complete determination of elastic stiffness coefficients and local symmetry breaking in the paraelectric barium titanate

The temperature dependence of all independent elastic stiffness coefficients of cubic BaTiO3 was determined over a wide temperature range from 400 degrees C to the Curie point (T-c similar to 131 degrees C) by using Brillouin light scattering spectroscopy. Among the two elastic eigen-modes corresponding to the two measured transverse acoustic waves, (C-11-C-12)/2 showed a large softening in the paraelectric phase, while the change in C-44 was very small. This result caused the elastic anisotropy A, defined as 2C(44)/(C-11-C-12),to increase from similar to 2.1 to similar to 2.7 upon cooling toward the phase transition temperature. The large elastic anisotropy was attributed to the tetragonal instability and the associated anisotropic polarization fluctuations of precursor polar clusters formed by the correlated Ti motions. The elastic anisotropy was fitted by using the Curie-Weiss law resulting in a significant deviation in a certain temperature range between T-c and similar to T-c + 50 degrees C, similar to the dielectric permittivity. Published under license by AIP Publishing.