Physicochemical characteristics of mixed copper-cadmium sulfides prepared by coprecipitation

A series of Cu-Cd sulfides were prepared by coprecipitation in aqueous supersaturated solutions at 25 degrees C, pH 2.50. The solids obtained were characterized by powder X-ray diffraction and their elemental composition was determined by chemical analysis. The results showed that in all cases mixed CuS-CdS precipitates were prepared, the ratio of each phase depending on the composition of the supersaturated solutions. A series of precipitates, of (CuS)(x) (CdS)(1-x), were prepared with x = 0.0, 0.20, 0.25, 0.30, 0.35, 0.50, and 1.0. All polycrystalline preparations with x = 0.30 showed metallic behavior typical for CuS, while the mixed sulfides with x = 0.20 and 0.25 showed semiconducting behavior, which however could not be described by any of the models reported in the literature. The band gap energies of 2.40 and 2.39 eV calculated for the two preparations showed that at this composition the material was dominated by the behavior of CdS. The activation energies estimated from the dependence of the solids conductivity on the temperature supported these results. Measurements of the current density at the preparations (x = 0.20 and 0.25) -polypyrrole and Al junctions yielded low values. More promising behavior was shown by the mixed sulfide-polypyrrole junctions, which yielded relatively higher current densities and higher stability.