Transport properties ofCoGe1.5Se1.5

We have synthesized and characterized polycrystalline $n$- and $p$-type ${\mathrm{CoGe}}_{1.5}{\mathrm{Se}}_{1.5},$ a member of the class of compounds with the skutterudite crystal structure. Both specimens have large room temperature Seebeck coefficients and resistivities. The carrier type depends very sensitively on the atomic ratio between Ge and Se. For both specimens, the carrier mobilities are very low and the thermal conductivity is lower than that of the binary skutterudite ${\mathrm{CoSb}}_3.$ Some of these properties can be attributed to the vacancies in the crystal lattice due to the nonstoichiometric nature of the specimens studied. The transport properties are compared with those of ${\mathrm{CoSb}}_3,$ and the potential for thermoelectric applications is discussed. This work is part of a continuing effort to explore the large phase space of many possible compositions of skutterudites, a promising class of high-efficiency thermoelectric materials.