Investigation of band gap effect on Raman shift of scheelite PbWO4 studied by Raman spectrometry and first-principles calculations

The Raman frequency shifts of the B-g (58 cm(-1)) and Ag (906 cm(-1)) in the PbWO4 were measured in the temperature range from 4 K to 500 K. We found that the frequency shift of A(g) (906 cm(-1)) shows interesting characteristic of positive change with increasing temperature. The temperature dependence of the Raman shift of these modes was analyzed using both the first-principles calculations and lattice perturbative approach. We found that the quartic anharmonic term of the first-order perturbation, as well as the second order one, and thermal expansion contribute to the temperature dependence of the frequency shift of A(g) (906 cm(-1)).