Effect of Cu Substitution on Thermoelectric Properties of Ge Clathrates

Abstract

We have prepared polycrystalline n-type Ba₈Cu_xGa_yGe_46−x−y (x=0–5, y=16−3x) clathrate compounds by arc melting and spark plasma sintering techniques and investigated the effect of Cu substitution for Ge on their thermoelectric properties. The Hall carrier concentration for Cu-substituted compounds is almost constant at the order of 10²⁰ cm⁻³, which is comparable to that for Ba₈Ga₁₆Ge₃₀ stoichiometric compounds. The Seebeck coefficient for these compounds is comparable to that for n-Ba₈Ga_yGe_46−y compounds. From the analysis of the properties, the effective mass of the conduction band is estimated to be about 1.4 m₀, which is equivalent to or slightly smaller than that of n-Ba₈Ga_yGe_46−y compounds. The Hall mobility increases as the Cu composition increases. Its temperature dependence obeys approximately T^−1⁄2 dependence in the range of 80–300 K, indicating the dominance of the alloy disorder scattering. Two models are discussed to account for the reduction in the alloy disorder scattering by Cu substitution.