Thermodynamic properties of nickel—selenium alloys

Vapor pressures of selenium in nickel—selenium alloys were determined by an isopiestic method between 450° and 1000°C and between 45 and 66.6 at% Se. Activities of selenium were evaluated according to three methods. For the NiAs-type Ni_1?x Se phase a statistical model was applied assuming random distribution of metal atoms and metal vacancies in the partially vacant (00 1/2) layers of the lattice. Good agreement between experimental and theoretical values was obtained. The interaction energy between nickel vacancies was found to be 8600 cal/g-atom.