INVESTIGATION OF THE RELATIVE STABILITY OF SOLID-PHASES IN THE LA-GRAPHITE SYSTEM BASED ON THE METHOD OF MULTICENTER ATOM-ATOM POTENTIALS

The relative stability of crystalline phases of the lanthanum-carbon s ystem with metal contents up to 33.3 at. % is investigated using the m ethod of semiempirical atom-atom potentials. It is shown that the stab ility of these phases depends on the stoichiometry, the structure and degree of order of the lattice, and also on the crystal size. Among th e bulk phases, the most stable is a phase with the calcium carbide str ucture, followed by phases with the metal graphitide and fluorite stru ctures. 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 ca rbide to graphitide easier, especially when the him of lanthanum-carbo n compound is grown on the surface of single-crystal graphite. (C) 199 7 American Institute of Physics.