Effect of Cu substitution on thermoelectric properties of Ge clathrates

Abstract

We have prepared polycrystalline n-type Ba 8Cu 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 10 20cm -3, which is comparable to that for Ba 8Ga 16Ge 30 stoichiometric compounds. The Seebeck coefficient for these compounds is comparable to that for n-Ba 8Ga yGe 46-y, compounds. From the analysis of the properties, the effective mass of the conduction band is estimated to be about 1.4m 0, which is equivalent to or slightly smaller than that of n-Ba 8Ga 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. © 2005 The Thermoelectrics Society of Japan.