Enthalpies of formation of cds _xse _1-x solid solutions

The enthalpies of oxidative drop solution (AH _ds) for a series of CdS _xSe _1-xsamples were obtained by calorimetry in molten 3Na ₂0-4MoO ₃ at 975 K. They become more exothermic linearly with increasing S content. The enthalpies of formation from the elements (AH _f,el) depend linearly on molar ratio of S/(S + Se). This is the first report of thermodynamic properties of CdS _xSe _1-x solid solutions measured by any direct calorimetric method. The enthalpies of formation at 298 K from the binary chalcogenide end-members (△H _f,cdm) (M = S, Se) for wurtzite CdS _xSe _1-x are found to be zero within experimental errors. These results strongly suggest that wurtzite CdS and CdSe form an ideal solid solution, despite a substantial difference in molar volume and anion radius. This implies that size difference affects thermodynamics less strongly when larger and more polarizable anions are mixed in chalcogenides than when cations are mixed in oxides.