The boundaries of thermodynamic stability of "classical" noble gas crystals and the problem of polymorphism
V.N. Bondarev and D.V. Tarasevych
НИИ физики Одесского национального университета им. И.И. Мечникова, ул. Пастера, 27, г. Одесса, 65082, Украина
Received December 8, 2010, revised Juanuary 25, 2011
The equations of the statistical theory of crystals with the pair interaction by Lennard-Jones are used to calculate the thermodynamic stability domain of hypothetical bcc phase discussed in the literature for the Ar type crystals. It is shown that this domain is wholly arranged inside an analogous domain previously calculated by the authors for a real fcc phase of such crystals. This result renders improbable the realization of the bcc phase predicted by a group of authors in the computer simulations on Xe at high temperatures and pressures, and was provoked a critical discussion in the literature. In addition, the quantum corrections to
the thermodynamic functions of “classical” noble gas crystals are considered and the deviation of the spinodal line of Ne from the “universal” one is calculated. The obtained results are in good quantitative agreement with the computer simulation data for the model (with the Lennard-Jones interaction) “crystals” of Ar, Kr, Xe as well as of Ne in the “exotic” domain of negative pressures. Although there are no current experimental indications of the polymorphic transformation of Ne into a modification other than fcc the
discovery of this phenomenon in the predicted range of temperatures T < 70 K and pressures p > 0.3 GPа should be of principle interest.
PACS: 64.10.+h General theory of equations of state and phase equilibria; PACS: 64.60.Bd General theory of phase transitions.
Key words: noble gas crystals, quantum effects, spinodal.