Investigation of the phonon band gap effect on Raman-active optical phonons in BaWO4 crystal

The phonon-dispersion relations of BaWO4 crystal are calculated using the lattice dynamical calculations approach. Spontaneous Raman spectra in the BaWO4 were measured in the temperature range from 10 K to 295 K, and the temperature dependence of the linewidth of the Eg (72 cm−1) and Ag (926 cm−1) Raman modes were 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 one-phonon density of states (PDOS) resulting in different anharmonic interactions. This phonon band gap limits the number of relaxation mechanisms for internal vibronic modes, i.e., anharmonic processes between the Ag (926 cm−1) Raman modes and lower energy modes in BaWO4. This leads to a dephasing effect on the Ag (926 cm−1) mode and the dephasing processes are increased only at high temperatures.