Reply to "Comment on 'Temperature-induced structural phase transition in CaBr2 studied by Raman spectroscopy' "

Abstract

It has been established by the Raman studies of Raptis, McGreevy, and Sequier [Phys. Rev. B 39, 7996 (1989)], and Hahn and Unruh (preceding paper [Phys. Rev. B 43, 12 665 (1991)]) that ${\mathrm{CaBr}}_{2}$ undergoes a temperature-induced second-order phase transition (${\mathit{D}}_{2\mathit{h}}$\ensuremath{\rightarrow}${\mathit{D}}_{4\mathit{h}}$) associated with a soft mode of the lower-symmetry phase. In our studies, detailed high-resolution Raman measurements (down to a low-frequency limit of 10 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) in ${\mathrm{CaBr}}_{2}$ and its isomorphous ${\mathrm{CaCl}}_{2}$ over wide temperature ranges (especially in the case of ${\mathrm{CaCl}}_{2}$) above ${\mathit{T}}_{\mathit{c}}$ have not revealed any soft-mode behavior, implying that the soft mode is Raman inactive in the higher-symmetry phase. This experimental evidence justifies, on the whole, the assignment of Raman modes made by Raptis, McGreevy, and Seguier, which has been partly disputed by Hahn and Unruh.