Physicochemical characteristics of mixed copper-cadmium sulfides prepared by coprecipitation

A series of Cu-Cd sulfides were prepared by coprecipitation in aqueous supe rsaturated solutions at 25 degrees C, pH 2.50. The solids obtained were cha racterized 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 t he composition of the supersaturated solutions. A series of precipitates, o f (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 metall ic behavior typical for CuS, while the mixed sulfides with x = 0.20 and 0.2 5 showed semiconducting behavior, which however could not be described by a ny 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 composi tion the material was dominated by the behavior of CdS. The activation ener gies estimated from the dependence of the solids conductivity on the temper ature supported these results. Measurements of the current density at the p reparations (x = 0.20 and 0.25) -polypyrrole and Al junctions yielded low v alues. More promising behavior was shown by the mixed sulfide-polypyrrole j unctions, which yielded relatively higher current densities and higher stab ility.