PREPARATION AND CHARACTERIZATION OF CU(II), ZN(II) SULFIDES OBTAINED BY SPONTANEOUS PRECIPITATION IN ELECTROLYTE-SOLUTIONS

Transition metal sulfides, because of their electronic and spectroscop ic properties, are a very interesting class of materials that may be u sed efficiently for the construction of photoelectric chemical solar c ells. In the present work we have prepared a series of mixed Cu and Zn sulfides with the general stoichiometry CuxZn1-xS 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 s ulfide 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 prese nce of metallic conducting islands separated by nonconducting parts, f or 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 p article size of the precipitates varied with increasing Zn content, yi elding for pure CuS, prismatic crystals with a mean size of similar to 5 mu m. Upon increasing Zn content, polycrystalline materials were ob tained, forming aggregates of submicron, spherullitic particles. The m easurements of the electrical properties of the materials showed that the conditions of precipitation play an important role for the design of their properties.