Anharmonicity on Raman active phonon modes of LaGaO₃

The phonon-dispersion relations of LaGaO₃ crystal are calculated using the first-principle calculations. The first-order Raman spectra in the LaGaO₃ were measured in the temperature range 20-690K. The temperature dependence of linewidth of several modes [the A_g(57 cm^-1) and the B_2g(118 cm^-1) for the low-temperature phase (LT), and the E_g(52 cm^-1) and the E_g(160 cm^-1) for the high-temperature phase (HT)] was analyzed using TDOS due to cubic term. The calculated results reproduce the observed ones in this temperature range without the temperature range (350-400 K) on the precursor effect of the phase transition. Temperature dependence of the linewidth for some rotational modes [the A_g(57 cm^-1) and the B_2g(118 cm^-1) for the LT, and the E_g(52 cm^-1) for the HT] is dominated by the scattering of a thermal phonon by the observed phonon, while that for the bending mode [the E_g(160 cm^-1) for the HT] is dominated by both the scattering and the decay of the observed phonons into two phonons having lower energies. We found that this originates in the large frequency gap in the DOS that produces a difference in anharmonic effects on each peak's channels in the HT.