The temperature dependence of the A1g-mode Raman line of MgF2

The first-order Raman spectrum for the A 1g mode of an MgF 2 single crystal was measured at various temperatures from 301 to 973 K. The frequency shift and linewidth change significantly with increasing temperature. In order to analyse the temperature dependence of the frequency shift, first the authors calculated the anharmonic force constants of an MgF 2 crystal. Then applying the lattice-dynamical perturbative treatment to the third- and fourth-order proper self-energy, they evaluated each contribution from the cubic and quartic anharmonic terms to the whole shift and could explain the frequency shift throughout the whole range of temperatures. They found that the cubic as well as quartic anharmonic terms play an important role in the temperature dependence of the Raman frequency shift for the A 1g mode.