First-order Raman spectra and lattice dynamics of aNdGaO3crystal

Abstract

The phonon-dispersion curves of the ${\mathrm{NdGaO}}_{3}$ crystal are calculated on the basis of a rigid-ion model by using the measured frequency values by Raman and infrared polarized spectroscopy at room temperature. The temperature dependence of the molar heat capacity of ${\mathrm{NdGaO}}_{3}$ is also calculated using the one-phonon density of states obtained from the phonon-dispersion curves. The first-order polarized Raman spectra of the ${A}_{1g}$ mode in the ${\mathrm{NdGaO}}_{3}$ crystal have been measured in the temperature range between 31 and 500 K. The temperature dependence for the linewidth of the ${A}_{1g}$ modes has been analyzed at 339 and 470 ${\mathrm{cm}}^{\ensuremath{-}1}$ by using the phonon-dispersion curves, and the calculated result reproduces the observed one in the temperature range 31--500 K. Thus, the temperature dependence of the linewidth of the ${A}_{1g}$ modes in the ${\mathrm{NdGaO}}_{3}$ crystal is approximately explained by the cubic anharmonic term in the expansion series of the crystal potential energy.