Correlation between thermopower and carrier mobility in the thermoelectric semimetal Ta2PdSe6

We have investigated the transport properties of single crystals of a thermoelectric semimetal Ta2PdSe6 and its niobium-substituted (Ta1−xNbx)2PdSe6 by means of resistivity, thermopower, and Hall resistivity measurements. The residual resistivity ratio systematically decreases by the Nb-substitution, indicating enhanced impurity scattering. The slope and peak-top value of thermopower also systematically decrease upon increasing x. We have analyzed the set of transport data by using a two-carrier model, then revealed strong correlation between the thermopower and carrier mobility in the titled compound. We propose that controlling carrier mobility is a possible route to achieve a high-performance thermoelectric semimetal.