Crystal structure and melting in a cell model. II. First-order transitions and metastable states

Abstract

For Pt.I, see ibid., vol.4, 717 (1971). The detailed thermodynamics of the cases of the cell model in paper I is considered. The one-dimensional systems have a first-order melting transition if the interactions extend beyond nearest-neighbour cells. The nearest-neighbour case has a second-order transition. First order transitions also occur for a triangular lattice with nearest-neighbour interactions, a square lattice with first- and second-neighbour interactions, and others. The isotherms for the first-order transitions closely resemble those obtained numerically for a hard square lattice gas by Bellemans and Nigam. The antiferromagnetic version of the cell model on a triangular lattice has two different ordered states and two transitions. Metastable states are defined and located for both the fluid and crystalline phases, and have some surprising features.