Properties of Cu(II) and Ni(II) Sulfides Prepared by Coprecipitation in Aqueous Solution

Among semiconductors, metal sulfides are very interesting materials that may be used for solar energy conversion arrangements. The authors prepared a series of Cu{sub x}Ni{sub 1{minus}x}S powders, where x = 0.05, 0.20, 0.50, and 0.80, by spontaneous precipitation. Various stoichiometries of Cu(NO{sub 3}){sub 2}, Ni(NO{sub 3}){sub 2}, and (NH{sub 4}){sub 2}S solutions at 25 C and pH 2.50, at conditions in which the aqueous solutions were supersaturated with respect to CuS and NiS, yielded precipitates corresponding to intermediate mixed sulfides. The appearance of new peaks in the powder X-ray diffraction spectra suggested the formation of new phases. Measurements of the resistance of the bulk solids as a function of temperature for the preparations with x = 0.05, 0.20, and 0.50 showed a decrease with increasing temperature. A hysteresis was found upon thermal cycling of the sulfide preparations, possibly due to changes in the solid state that affect the energy bands of the semiconductors. The Cu and Ni sulfide preparations with x = 0.80 showed metallic behavior. All preparations were highly charged with suspended in aqueous media, and the electrical charge was found to depend strongly on the activity of copper ion in solutions equilibrated with the solid phase. Finally, currentmore » potential curves of electrodes prepared from the precipitated sulfides under constant illumination gave values for the open circuit potential as high as 0.868 V, with 0.119 mA for the photocurrent and 0.58 for the field factor. These values are encouraging for the potential application of these materials in cells for the conversion of solar into electric energy.« less