Effect of chemical pressure manipulation on the valence and thermoelectric properties of the intermediate valence compound YbCu2-xNixGe2

Abstract

The thermoelectric properties of YbCu 2 Ge 2 at low temperature are unremarkable, however it has been found to be an intermediate valence compound. Previous work has shown that manipulation of valence in such compounds by chemical pressure can have dramatic effects on the value of the Seebeck coefficient. YbCu 2 Ge 2 has been found to exist in a nearly divalent, Yb 2+ , state at room temperature, which if increased towards 2.5 has the promise of increasing the Seebeck coefficient substantially. In this study a full solid solution of YbCu 2 Ge 2 and YbNi 2 Ge 2 was created to exert a chemical pressure on the Yb and shift the valence away from the nominally divalent. A dramatic increase in the Seebeck coefficient was found as well as a substantial decrease in the thermal conductivity. These effects resulted in a substantial increase in ZT at low temperature and further emphasized the applicability and large effect that valence manipulation can have on intermediate valence compounds.