INFLUENCE OF HYDROSTATIC PRESSURE ON RAMAN SPECTRA OF epsilon -GaSe AND ZnIn2S4 SINGLE CRYSTALS.

An investigation was made of the influence of hydrostatic pressures on the Raman spectra of epsilon -GaSe (up to 8. 5 kbar) and of ZnIn//2S//4 (up to 10. 9 kbar) at 295 degree K. The values of the parameter gamma //i equals (1/ nu //i)(d nu //i/dP) were determined for both single crystals, and in the case of epsilon -GaSe the mode Gruneisen parameters GAMMA //i were also found. The set of the parameters gamma //i( GAMMA //i) indicated that both crystals had a layer structure with a mixed ionic-covalent binding within the layers. The parameters gamma //i were used to find the number of vibrations in ZnIn//2S//4 (by analogy with epsilon -GaSe) belonging to the ″rigid layer″ type (i. e. , interlayer vibrations). The results showed that ZnIn//2S//4, like epsilon -GaSe, was most likely a two-layer polytype.