Effect of Europium Substitution on Thermoelectric Properties of Noble-Metal Silicon Clathrates with Ba8-xEuxCuySi46-y Nominal Compositions

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 Ba8-xEuxCuySi46-y (x = 0, 1, 2; y = 4, 5, 6). The Seebeck coefficient and the electrical conductivity of the rare-earth-substituted Ba8-xEuxCuySi46-y samples are consistent with n-type conduction and metal-like behavior. The Hall carrier mobility of Ba8-xEuxCu6Si40 at room temperature decreases with increasing Eu substitution. The conduction band effective mass of rare-earth-substituted Ba8-xEuxCu6Si40 (x = 1, 2) is experimentally estimated to be larger than that of Ba8Cu6Si40. On the basis of ab initio electronic structure calculations for Ba6Eu2Cu6Si40 and Ba8Cu6Si40, it is deduced that the conduction band edges of Ba8Cu6Si40 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. [doi:10.2320/matertrans.E-M2012816]