ORDERING IN BXC1-X COMPOUNDS WITH THE GRAPHITE STRUCTURE

We present a theoretical study of the structural stability of ordered configurations of BxC1-x solid solutions with the graphite structure. The calculations were carried out self-consistently using norm-conserv ing pseudopotentials in the local-density approximation. The cohesive energies of a number of ordered structures at different compositions x have been subjected to a cluster expansion, which enables us to predi ct the cohesive energy of the random alloy at the corresponding compos itions and to gain insight on the tendency of the system towards order ing. We find that, at T = 0 K, some ordered configurations have a cohe sive energy higher than the corresponding random distribution at the s ame compositions. The inspection of the cluster interactions leads mor eover to the conclusion that segregation of boron in graphite is highl y discouraged and long-range order is likely to occur.