Ultraviolet Laser Raman Spectroscopy on Sr₂Nb₂O₇ at High Temperature to Estimate Chemical Bonds

Abstract

Raman spectra of Sr₂Nb₂O₇ have been successfully obtained at temperatures up to 1643 K for the first time, using a continuous-wave ultraviolet Raman spectroscopic system designed to measure the Raman scattering from materials at high temperature. The Raman spectra of Sr₂Nb₂O₇ with a symmetry of Cmc2₁ are described in terms of the parameter related to temperature variation at constant pressure, defined in a similar way to the Gruneisen parameter. By means of comparing vibrational modes of Sr₂Ta₂O₇, the higher frequency modes located above 210 cm^-1 are assigned to NbO₆ internal modes. The parameter of NbO₆ internal modes is as large as that of lattice modes, reflecting the weak chemical-bond strength of Nb–O bonds.