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Single-Crystal Growth and Thermoelectric Properties of Ge(Bi,Sb)4Te7

The thermoelectric properties between 10 and 300 K and the growth of single crystals of n-type and p-type GeBi4Te7, GeSb4Te7, and the Ge(Bi1-xSbx)4Te7 solid solution are reported. Single crystals were grown by the modified Bridgman method, and p-type behavior was achieved by the substitution of Bi by Sb in GeBi4Te7. The thermopower in the Ge(Bi1-xSbx)4Te7 solid solution ranges from -117 muVK^-1 to +160 muVK^-1. The crossover from n-type to p-type is continuous with increasing Sb content and is observed at x = 0.15. The highest thermoelectric efficiencies among the tested n-type and p-type samples are ZnT = 0.11 and ZpT = 0.20, respectively. For an optimal n-p couple in this alloy system the composite figure of merit is ZnpT = 0.17 at room temperature.