Raman Spectrum in Monoclinic BiVO₄

Abstract

A boule of BiVO 4 single crystal was grown by Czochralski technique and annealed for 24 hours at 500°C. The Laue and conoscopic image techniques were used to determine the crystallographic axes of BiVO 4 single crystal. The Raman spectrum of c(bb)c̄ geometry of monoclinic BiVO 4 was obtained and the A g symmetry mode appearing at 56 cm -1 at room temperature was softened as the temperature approached to the ferroelastic-paraelastic phase trasition point (255°C). The disappearing of soft A g mode at phase transition temperature indicates that it is closely related to the ferroelastic strain which controlles the phase transition, i.e., ferroelastic-paraelastic phase transition in BivO 4 .