A Monte Carlo Study of Disorder in the High Pressure Mixed Crystal N₂-Ar

Abstract

In order to obtain a better notion of the experimental results in our laboratory, Monte Carlo calculations have been performed of the N ₂-Ar crystal on the N ₂-rich side, in the p-T region where the ε and δ phases exist in pure N ₂. Considering the enthalpy, the system prefers the Ar atoms to be located on the sphere positions. The ε* phase is present for mixtures down to $x_{N_2 } = 0.90$ but is most likely metastable. The ε*-δ* transition shifts to lower temperatures with decreasing $x_{N_2 }$. The 2 ^nd order transition within the δ phase continues to exist to even smaller $x_{N_2 }$. In contrast to the ε* -δ* transition, the transition temperature for the 2 ^nd order transition does not shift to lower temperatures. For a mixture of $x_{N_2 } = 0.83,$ it is within 5 K from the pure 2 ^nd order transition at a pressure of 7.0 GPa.