Preparation and Characterization of Cu(II), Zn(II) Sulfides Obtained by Spontaneous Precipitation in Electrolyte Solutions

Transition metal sulfides, because of their electronic and spectroscopic properties, are a very interesting class of materials that may be used efficiently for the construction of photoelectric chemical solar cells. In the present work we have prepared a series of mixed Cu and Zn sulfides with the general stoichiometry Cu x Zn 1 - x S by coprecipitation in aqueous solutions. Precipitates with x = 0.10, 0.15, 0.20, 0.22, 0.25, and 0.50 were synthesized by mixing metal nitrates with ammonium sulfide at pH 2.50. The precipitates behaved as n -type semiconductors. The dependence of the conductivity of the materials on temperature and calculations of the thermoelectric power coefficient showed the presence of metallic conducting islands separated by nonconducting parts, for copper content corresponding to x = 0.15, 0.20, and 0.22. For x = 0.10, the precipitates behaved as insulators, whereas for x = 0.50, the precipitates showed metallic character. The morphology and the mean particle size of the precipitates varied with increasing Zn content, yielding for pure CuS, prismatic crystals with a mean size of ∼5 μm. Upon increasing Zn content, polycrystalline materials were obtained, forming aggregates of submicron, spherullitic particles. The measurements of the electrical properties of the materials showed that the conditions of precipitation play an important role for the design of their properties.