High-Pressure Brillouin Study on Solid NH₃

Abstract

Adiabatic elastic constants and adiabatic bulk modulus have been determined for the orientationally disordered phase III (plastic phase) of NH₃ at pressures up to 3. 5 GPa at room temperature, by Brillouin measurements with in situ identification for the orientation of single crystal NH₃ in a diamond anvil cell. Typical values of three elastic constants for f. c. c, crystalline NH₃ are C₁₁=21. 1, C₁₂=17. 1, and C₄₄=8. 1 GPa at pressure of 2. 56 GPa. The elastic anisotropy (A=4. 06 at 2. 56 GPa) is almost constant against pressure, and these properties are compared with those of other plastic solids.