Raman spectra of single crystals TlGaS2 and TlGaSe2 are investigated in equilibrium conditions at room temperature under various hydrostatic pressures up to 7.25 and 9.27 kbar, respectively. Phase transitions at about 5 kbar are shown to occur in both the single crystals. Mode parameters γi = (1/vi) (dvi/dP) are determined for most of the Raman bands observed. The different values of these parameters are used to find out which frequencies have to be assigned to interlayer vibrations. It is shown that Raman spectra can be explained best when the unit cell of TlGaS2 and TlGaSe2 is supposed to contain two layers and the structure of the layer is supposed to be similar to that of TlSe.

No abstract

The influence of hydrostatic pressure on the Raman scattering spectra in e- GaSe (up to 8.5 kbar) and ZnIn,S, (up t o 10.9 kbar) is investigated a t 295 K. Parameters Y{ = (l/vc) (dv,/dp) are obtained for both the single crystals; for E-GaSe values of the mode-Gruneisen parameters are also obtained. The set of the parameters ye(r,) shows that these two crystals are layered ones with ionic-covalent bonds inside the layers; the degree of ionicity in ZnIn,S, is higher than in c-GaSe. "Rigid-layer" (interlayer) vibrations determined for ZnIn,S, and E-GaSe using yi-parameters show that ZnIn,S, is not a one-packet polytype.

No abstract

No abstract