Thermodynamics and microstructure of vacancies in rare gas crystals at high temperature

A self-consistent statistical method is used to calculate the Gibbs free energy of vacancy formation in heavy rare gas crystals at high temperature. It is shown that the vacancy formation free energy rapidly falls in the vicinity of the melting point of the crystal. Such behavior is attributed to approaching the anharmonic instability point of vibrational subsystem of the solid

Influence of vibrational anharmonicity and vacancies on thermodynamic properties of the rare gas crystals

A statistical method is used to calculate thermodynamic properties of Ar, Kr and Xe (isobaric and isochoric heat capacity, bulk modulus, thermal expansion coefficient, interatomic distances, Grüneisen parameter), and good agreement with experimental values is observed. It is shown that at high temperature, slightly above the melting point of the rare gas crystals, an instability of the crystalline state occurs. As temperature approaches this instability the isobaric heat capacity and the thermal expansion coefficient show strong increases similar to the experimentally observed anomalies

Melting and thermodynamic properties of rare gas nanocrystals

A self-consistent statistical method [Phys. Rev. B66, 054302 (2002)] is used to describe thermodynamic properties of free rare gas nanocrystals using thin plates as examples. It is shown that size influence on thermodynamic properties of nanocrystals is caused by size-dependent quantization of the vibration spectrum affecting the parameters of a statistical distribution function of atomic displacements and, thus, governing size dependence of average values of energetic contributions to the Gibbs free energy of the system. For Xe nanocrystals, we present calculated size dependences of the Debye temperature, heat capacity, interatomic distance, melting temperature, etc

Effect of Crystal Quality on HCP-BCC Phase Transition in Solid 4He

The kinetics of HCP-BCC structure phase transition is studied by precise pressure measurement technique in 4He crystals of different quality. An anomalous pressure behavior in bad quality crystals under constant volume conditions is detected just after HCP-BCC structure phase transition. A sharp pressure drop of 0.2 bar was observed at constant temperature. The subsequent pressure kinetics is a non-monotonic temperature function. The effect observed can be explained if we suppose that microscopic liquid droplets appear on the HCP-BCC interphase region in bad quality crystals. After the interphase region disappearance, these droplets are crystallized with pressure reduction. It is shown that this effect is absent in high quality thermal-treated crystals.Comment: 4 pages, 4 figure

Thermodynamic properties of cubic boron nitride based on an analytic mean field approach

05.70.Ce Thermodynamic functions and equations of state, 65.40.-b Thermal properties of crystalline solids,