Effect of europium substitution on thermoelectric properties of noble-metal silicon clathrates with Ba 8-xEu xCu ySi 46-y nominal compositions

Abstract

The effect of the substitution of a rare-earth element for a guest element on the electronic and thermoelectric properties is investigated for clathrates with the nominal composition Ba 8-xEu xCu ySi 46-y (x = 0, 1, 2; y = 4, 5, 6). The Seebeck coefficient and the electrical conductivity of the rare-earth-substituted Ba 8-xEu xCu ySi 46-y samples are consistent with n-type conduction and metal-like behavior. The Hall carrier mobility of Ba 8-xEu xCu ySi 40 at room temperature decreases with increasing Eu substitution. The conduction band effective mass of rare-earth-substituted Ba 8-xEu xCu 6Si 40 (x = 1, 2) is experimentally estimated to be larger than that of Ba 8Cu 6Si 40. On the basis of ab initio electronic structure calculations for Ba 6Eu 2Cu 6Si 40 and Ba 8Cu 6Si 40, it is deduced that the conduction band edges of Ba 8Cu 6Si 40 are modified by the substitution of Eu for the guest atom Ba, resulting in an increase in the density-of-states effective mass, which is consistent with the experimental result. © 2012 The Thermoelectrics Society of Japan.