報文

Infrared Phonon Spectra and Lattice Dynamics for NdGaO₃

Jun SUDA and Tsutomu SATO
須田　潤・佐藤　孜

　Polarized infrared reflected spectra of NdGaO₃ crystal are measured at room temperature. The Infrared-active phonon frequencies, linewidths and the dielectric constants are obtained by oscillator fitting procedure of the reflective data measured at room temperature. The phonon dispersion curves of NdGaO₃ are calculated using a shell model. The B_2u mode at 174 cm^-1 involves mixed vibrations of the Nd atoms and GaO₆ octahedra, and the higher frequency mode do not involve motion of Nd atoms above 300 cm^-1. The linewidth of B_2u mode has been analyzed at 174 cm^-1, 356 cm^-1, and 595 cm^-1 using the lattice dynamical perturbative treatment within the cubic anharmonic term in the expansion series of the crystal potential energy, and the calculated results reproduces the observed ones at room temperature. We found that the linewidth of the B_2u mode (174 cm^-1) varied with increasing temperature by comparison with other phonon peaks (356 cm^-1, and 595 cm^-1).

Keywords:　Infrared reflected spectra, Phonon dispersion curve, Shell model, Two-phonon density of states and cubic anharmonic term