Comment on ‘‘Silent soft mode in hexagonal barium titanate observed by hyper-Raman scattering’’

Abstract
The soft zone-center E2u mode was recently observed by means of hyper-Raman scattering by Inoue et al. [Phys. Rev. B 38, 6352 (1988)]. Knowing that the E2u mode drives the transition, we obtain the lower-symmetry space group of the transition, construct the free energy (including elastic coupling), and show the possible optical modes allowed by symmetry.