Linking tracks in mica crystals with phase transitions in a bistable lattice

Abstract

Since the middle of the last century, scientific research has been conducted to explain the nature of the tracks visible to the naked eye in mica muscovite crystals. In the present work, an attempt to link the appearance of tracks with a phase transition in a bistable medium is made using classical molecular dynamics method. For this purpose, a two-dimensional triangular lattice simulating one row of potassium atoms in mica is considered. Interactions between atoms are described via pairwise Morse potential and a local potential, whose minima create a hexagonal lattice. In order to create a bistability in the system, a mismatch between the equilibrium distance of the triangular lattice and the period of the local potential is artificially introduced. The phase transitions arising from a monotonic increase or decrease of the depth of the local potential are described. It is revealed that at lower temperatures the domains of different phases can coexist, but at higher temperatures the domain with lower potential energy grows with heat release by reducing the high energy domain. It is speculated that the considered model, which provides the possibility of coexistence of two different phases, can be used to explain at qualitative level the nature of dark tracks visible with the naked eye in transparent crystals of mica muscovite.