Investigation of the relative stability of solid phases in the La-graphite system based on the method of multicenter atom-atom potentials

Abstract

The relative stability of crystalline phases of the lanthanum-carbon system with metal contents up to 33.3 at. % is investigated using the method of semiempirical atom-atom potentials. It is shown that the stability of these phases depends on the stoichiometry, the structure and degree of order of the lattice, and also on the crystal size. Among the bulk phases, the most stable is a phase with the calcium carbide structure, followed by phases with the metal graphitide and fluorite structures. In layers with thicknesses of a few nanometers, including 1–4 monolayer films, the energies of formation of lanthanum graphitide and carbide approach one another. This makes the phase transition from carbide to graphitide easier, especially when the film of lanthanum-carbon compound is grown on the surface of single-crystal graphite.