Mode softening in cubic BaTiO3and the problem of its adequate description

We compare recent infrared and hyper-Raman-scattering measurements on BaTi${\mathrm{O}}_3$ in its cubic paraelectric phase. By reinterpreting the experimental data of Inoue and Akimoto, we show that the low-frequency part of all hyper-Raman-scattering spectra so far reported can be adequately accounted for by a single highly overdamped classical oscillator which softens continuously when the Curie temperature is approached from above. We discuss the adequacy of more complicated models and estimate the degree of compatibility between the hyper-Raman-scattering data and the infrared results of Luspin et al.