Thermal-Expansion Measurements and Thermodynamics of Solid Krypton

Accurate measurements of the lattice parameter of krypton versus temperature are reported. The measurements allow precise evaluation of the volume expansivity as a function of temperature. These results, together with recent measurements of specific heat, isothermal compressibility, and equilibrium vacancy concentration, provide enough information to allow tabulation and discussion of a number of thermodynamic properties of solid krypton. It is found that the thermal formation of atomic vacancies has a significant effect on all the thermodynamic functions of krypton at the higher temperatures. Entropy and isochoric specific-heat values are analyzed to obtain the leading anharmonic coefficient in the high-temperature expansion for the free energy of krypton. Additional explicit evidence for anharmonicity comes from the observed systematic decrease of Gr\"uneisen parameter with increasing temperature. Finally, numerous published calculations of thermal properties of noble-gas solids are examined. It is concluded that no comprehensive model is presently available to predict the observed properties of krypton and argon within present experimental accuracy.

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