Enthalpies of formation of CdS_xSe_1–xsolid solutions

The enthalpies of oxidative drop solution (ΔH_ds) for a series of CdS_xSe_1–xsamples were obtained by calorimetry in molten 3Na₂O·4MoO₃at 975 K. They become more exothermic linearly with increasing S content. The enthalpies of formation from the elements (ΔH_f,el) depend linearly on molar ratio of S/(S + Se). This is the first report of thermodynamic properties of CdS_xSe_1–xsolid solutions measured by any direct calorimetric method. The enthalpies of formation at 298 K from the binary chalcogenide end-members (ΔH_f,CdM) (M= S, Se) for wurtzite CdS_xSe_1–xare 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.