Investigation of anharmonicity in rotational phonon mode for BaWO4 crystal

Abstract

Spontaneous Raman spectra in the BaWO4 were measured in the temperature range from 4K to 280K, and the temperature dependence of the linewidth of the Ag (191cm−1) Raman mode was analyzed using the lattice dynamical perturbative approach and one-phonon density of states (PDOS). The linewidth slope for the 191cm−1 peak for an external mode is 7.2 times larger than that for the 926cm−1 peak for a breathing mode. The different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the one-phonon density of states (PDOS) resulting in different anharmonic interactions. The origin may be that the ratio of up-conversion TDOS to down-conversion TDOS for Eg mode (191cm−1) is more than that for Ag (926cm−1). The peak of the Eg mode (191cm−1) is attributed to the coupling mode both a rotation of the Barium and an out-of-phase rotation of the oxygen in x–y plane as a librational mode.