Investigation of the phonon band gap effect on Raman-active optical phonons in SrMoO4 crystal

The phonon dispersions of SrMoO4 crystal are calculated using the lattice dynamical calculations approach. Spontaneous Raman spectra in the SrMoO4 were measured in the temperature range from 10 K to 295 K, and the temperature dependence of the linewidth of the Bg (95 cm−1) and Ag (888 cm−1) Raman modes was analyzed using the lattice dynamical perturbative approach. We found that different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the phonon spectrum resulting in different anharmonic interactions. The calculated temperature dependence of the linewidth of Ag (888 cm−1) mode was well accounted for the experimental one by including both down-conversion by the cubic term and the dephasing by quartic term. The dephasing processes are increased only at high temperatures and the effect of dephasing is related to the size of a large phonon band gap.