High-temperature thermoelectric properties of /spl alpha/- and /spl beta/-Eu/sub 8/Ga/sub 16/Ge/sub 30/

We present the thermoelectric properties of an /spl alpha/-Eu/sub 8/Ga/sub 16/Ge/sub 30/ and a /spl beta/-Eu/sub 8/Ga/sub 16/Ge/sub 30/ sample with a Ga/Ge ratio that deviates slightly from the ideal 16/30 ratio. Thermopower and resistivity have been measured up to 750 K. From an extrapolation of the thermal conductivity, measured up to 200 K, to higher temperatures we estimate the dimensionless figure of merit to have a maximum of 0.55 and 1.1 at 700 K and 750 K for the /spl alpha/ and /spl beta/ sample, respectively. The thermoelectric properties of the a sample are, at highest temperatures, degraded by the excitation of carriers into the conduction band.