Thermal and lattice dynamical properties of Na8Si46 clathrate - art. no. 024303

The experimental heat capacity of Na8Si46 has been determined from 35-300 K , and its lattice parameters have been measured over the range 100-330 K. T he experimental heat capacity and the thermal-expansion coefficient are com pared with theoretical lattice-dynamical calculations for Na8Si46. The latt er accurately reproduce the experimental thermal expansion and also give th e first reliable assignment of the vibrational spectrum of this material, a s judged by comparison of the calculated and experimental heat capacities. In addition, the theoretical results allow a calculation of the Gruneisen p arameter of Na8Si46, which shows enhanced anharmonicity at low temperatures .