ELASTIC COEFFICIENTS IN TLGA(S1-XSEX)2 AND TLINXGA1-XS2 LAYER MIXED-CRYSTALS BY BRILLOUIN-SCATTERING

The compositional variation of the elastic coefficients C-11 and C33 f or TlGa(S1-xSex) and TlInxGa1-xS2 layer mixed crystals are discussed u sing Brillouin scattering measurements. Clear anomalies are observed f or the longitudinal phonons propagating parallel to the (00 1) plane ( elastic coefficient C-11) at x(c) congruent-to 0.8 and x(c) congruent- to 0.3 in TlInxGa1-xS2 and TlGa(S1-xSex)2, respectively. These anomali es are explained by the formation of infinite clusters. A considerable difference in the rate of change of the elastic coefficient C33 with the composition for the mixed crystals TlGa(S1-xSex)2 and TlInxGa1-xS2 is observed. The temperature variation of C33 for a TlIn0.95Ga0.05S2 mixed crystals is also given and the results are discussed.