Thermodynamic properties of substoichiometric zirconium dioxide at the lower phase boundary

The vaporization behavior of the univariant system, Zr(s,1) + ZrO/sub 2/ (s), has been investigated by a combination of mass effusion and mass-spectrometric techniques over the temperature range 1900 to 2500/sup 0/K. The partial pressures of the gaseous species, Zr(g), ZrO/sub 2/(g), and O(g), across the miscibility gap and the activities and activity coefficients of Zr and ZrO/sub 2/ in the condensed phases have been determined. From these results values for the standard Gibbs energy of formation of the substoichiometric dioxide and the Zr(..cap alpha..) phase saturated with oxygen were calculated as a function of temperature and the corresponding compositions of the phase boundaries.