EXISTENCE OF A CO3AL PHASE ISOTYPICAL WITH CU3AU

Phase equilibria in the binary system Co-Al were investigated at concentrations between 25 and 32 at.% Al. Neither a stable nor a metastable phase Co3Al isotypical with Cu3Au was found by means of heat treatment or splat cooling techniques. Oxidation of powdered alloys yielded a cubic primitive phase, cP, a=3.6552(2) angstrom, observed in earlier investigations. The structure of this compound Co3AlOx is of the partially filled perovskite type. Comparing the average 3d electron densities of quasi-homologous phases, the possibility of the existence of a high pressure phase Co3Al(p) with Cu3Au structure is discussed.