Elasticity of single-crystal methane hydrate at high pressure

Abstract

By using in situ high-pressure Brillouin spectroscopy in a diamond-anvil cell, we have determined the pressure dependence of acoustic velocities, adiabatic elastic moduli, bulk modulus, elastic anisotropy, and Cauchy violation of single-crystal methane hydrate (MH) at pressures up to 0.6 GPa and 296 K. Acoustic velocities show nearly isotropic behaviors with respect to the crystal orientation, and the slight TA-mode softening with pressure implies that the structure of MH is becoming less stable against the shear component under high pressures. Elastic moduli and bulk modulus indicate that MH is slightly more compressible than ice $I_h.$ These results would help to investigate their mechanical and thermodynamical stabilities, and provide important constraints on the icy moons of the outer solar system.