Raman scattering in CdGa2Se4 under pressure

The Raman scattering spectra of CdGa2Se4 under pressure were investigated at 300 K up to 20.9 GPa. TO as well as LO modes were observed. Two stages were observed in the pressure dependences of Raman bands. Such a behaviour was attributed to the order-disorder phase transition in the cation sublattice. A first-order phase transition under pressure was observed at 20.2 GPa. Using the Harrison-Keating model of the lattice dynamics modified for crystals with the tetragonal structure, the bulk modulus B and the mode-Gruneisen parameters Gamma(i) were determined for the first time. It is shown that a better agreement between the experimental and calculated values of Gamma(i) is observed if one takes into consideration the different behaviour with pressure for the bond-bending and the bond-stretching parameters, which determine the low-(lower than 140 cm(-1)) and high-(higher than 140 cm(-1)) frequency phonons, respectively.