Raman scattering in CdGa₂Se₄ under pressure

Abstract

Abstract The Raman scattering spectra of CdGa 2 Se 4 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 ordedisorder phase transition in the cation sublattice. A first‐order phase transition under pressure was observed at 20.2 GPa. Using the HarrisoKeating model of the lattice dynamics modified for crystals with the tetragonal structure, the bulk modulus B and the mode‐Grüneisen parameters Γ i were determined for the first time. It is shown that a better agreement between the experimental and calculated values of Γ 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.