1998 Volume 47 Issue 10 Pages 1012-1018
High-pressure Brillouin scattering studies are described by presenting a total system for determinations of direction-dependent acoustic velocities, refractive index, adiabatic elastic constants, adiabatic bulk modulus, and elastic anisotropy in a simple molecular solid grown in a diamond-anvil cell. The detailed method is presented for an orientationally disordered phase III (1.0≤P≤3.5GPa) of a molecular solid NH3 at 300K. This phase III shows either the molecular rotation or the hydrogen bond. Typical values of three elastic constants are C11=21.1, C12=17.1, and C44=8.1GPa at P=2.56GPa. The elastic anisotropy, A=4.05 at 2.56GPa, is almost constant against pressure for fcc crystalline NH3. These properties are compared with those of solids CH4, Kr, H2S, HCl, and CO2, by concerning with the effects of the molecular rotation and the hydrogen bond under compression.
