High-pressure elastic properties of liquid and solid ammonia
Abstract
Acoustic velocity, adiabatic elastic constants, adiabatic bulk modulus, and the refractive index of liquid and solid NH3 were determined under pressures up to 3.5 GPa at room temperature, by Brillouin spectroscopy with in situ identification for the orientation of single crystal NH3 in a diamond-anvil cell. Values of three elastic constants and bulk modulus for fcc crystalline NH3 (phase III) are, e.g., C11=23.2, C12=18.8, and C44=8.9 GPa, and BS=20.2 GPa at a pressure of 3.0 GPa, respectively. The elastic anisotropy obtained from the elastic constants shows a large value (4.06 at 3.0 GPa), indicating that rotation-translation coupling of the molecular motions is effective in the orientationally disordered phase III. Comparisons of the pressure dependence of NH3 elastic anisotropy with those for other molecular solids suggest that the hydrogen bond influences on the molecular rotation under compression.
- Publication:
-
Physical Review B
- Pub Date:
- June 1998
- DOI:
- 10.1103/PhysRevB.57.13347
- Bibcode:
- 1998PhRvB..5713347K
- Keywords:
-
- 78.35.+c;
- 62.50.+p;
- 62.65.+k;
- 31.70.Ks;
- Brillouin and Rayleigh scattering;
- other light scattering;
- High-pressure and shock wave effects in solids and liquids;
- Acoustical properties of solids;
- Molecular solids