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CoSb3 skutterudites have been prepared by a new chemical method of co-precipitating the constituents from an aqueous solution and subsequent heat treatment at comparably low temperature, resulting in nano-grained powder and thus in a very high concentration of grain boundaries. Under certain conditions grain boundary scattering is expected to be more effective on heat carrying phonons than on charge carriers, causing an increased ratio of electrical to thermal conductivity (σ/κ ratio). Furthermore to overcome the expected reduction of the electrical conductivity by the grain boundary scattering skutterudites with various substitution of Co by Ni and of Sb by Te as well as combined substitutions have been prepared. Their structural and thermoelectric properties have been investigated, i.e. electrical and thermal conductivity as well as Seebeck coefficient and figure of merit. ZT values up to 0.67 at 680 K have been found for these samples.