Pressure Dependence of Raman Spectra in Low Frequency Region of Ferroelastic NdNbO₄

Abstract

Pressure dependence (up to ∼80 Kbar) of optical modes in low frequency region of NdNbO₄ was investigated by Raman scattering measurements at room temperature. The Raman spectra of NdNbO₄ are found to be quite similar to those of isostructural LaNbO₄. With increasing pressure, the overlapped peaks of the lowest frequency in NdNbO₄ at atmospheric pressure, which are in the different symmetries each other, split around 30 Kbar. This behavior can be explained by the coupling of the optical mode and the order parameter x₆.