Brillouin scattering from LA phonons in the layered semiconductor GaS has been measured in a diamond anvil cell up to 17.5 GPa. In the same range, linear compressibilities parallel and perpendicular to the c axis have been determined, as well as the ordinary and extraordinary refractive indices. From these data the variations of the elastic constants Cll and C33 and the sound velocities under pressure are deduced. Brillouin data at ambient pressure give the five independent elastic constants of GaS (D6q), and the compressibilities computed from this set of C;J are found to coincide with the values observed in the high-pressure measurements.The optical-index anisotropy decreases to negligible values above 14 GPa. Comparison with an anisotropic modification of Murnaghan's equation of state shows that under high pressure, interand intra-layer forces still retain their individual behavior, although the former have become comparable in magnitude with the latter. Brillouin scattering in the ethanol-methanol mixture has been measured up to 17.5 GPa and the variation of the elastic constant of the fluid is compared with Tait's and Murnaghan's equations of state.
Brillouin scattering in GaS crystals had been measured under hydrostatic pressures up to 17.5 GPa. Frequency shifts of the Brillouin lines give the pressure dependence of the elastic constants C11 and C33, and the index birefringence. Exponents derived from Murnaghan’s equation of state are compared with a Lennard-Jones description of interatomic forces in GaS.
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