High-temperature thermoelectric properties of α- and β-Eu8Ga16Ge30

We present the thermoelectric properties of an α-Eu₈Ga₁₆Ge₃₀ and a β-Eu₈Ga₁₆Ge₃₀ 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 α and β sample, respectively. The thermoelectric properties of the a sample are, at highest temperatures, degraded by the excitation of carriers into the conduction band.