Vibrational spectroscopic study of ferroelectric SbNbO4, antiferroelectric BiNbO4, and their solid solutions.

Abstract

Raman scattering and infrared absorption studies of ferroelectric SbNb${\mathrm{O}}_{4}$, antiferroelectric BiNb${\mathrm{O}}_{4}$, and the solid solution $({\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x})\mathrm{Nb}{\mathrm{O}}_{4}$ for $0<x<1$ in the range 20-1200 ${\mathrm{cm}}^{\ensuremath{-}1}$ are reported. These are the first vibrational spectroscopic investigations in these stibiotantalite-type systems. Symmetry assignments are proposed for the internal modes. Such an assignment is shown to lead to a consistent set of values for the local force constants calculated under the general quadratic valence force field. The nature of the variations of lattice and internal frequencies with changes in ${A}^{3+}$-ion concentration is qualitatively discussed with particular reference to the ferroelectric soft mode.