The roles of Yb-substitution on thermoelectric properties of In4−Yb Se3

Abstract Lead-free In 4 Se 3 is a newly established promising middle temperature n-type thermoelectric (TE) material candidate. Series of Yb-substituted In 4− x Yb x Se 3 ( x = 0.01–0.09) samples are prepared herein and their TE properties and the structure–property relationship are investigated. Magnetic molar susceptibility measurements indicate that Yb is nonmagnetic. However, the Yb doped samples behave abnormally in transport properties. The unit cell volume variations and the carrier concentration ( n e ) changes reveal that Yb substitutes the In4+ site when x 4 Se 3 and behaves in transport property as an +1 ion leading to a slow n e decrease; differently, Yb substitutes the In 3 5+ sites in the unitcell of In 4 Se 3 when x > 0.05, and behaves as an acceptor leading to a sharp n e decline. These are considered to be attributed to the Fermi level pinning of the f and d orbitals of Yb. Such Yb substitution preference is also supported by our primary formation energy calculation. Besides, the carriers that on the pinning level are highly localized, thus contribute very little to the electrical conductivity, but contribute to some degree to the thermal conductivity as shown by property-temperature plots. In addition, the Yb atoms produce resonate states around E F that enhance the Seebeck coefficient. As a heavy atom, Yb effectively scatter phonons resulting in the thermal conductivity reduction. All these factors together give In 3.95 Yb 0.05 Se 3 a significant 30% ZT at 703 K relevant to that of the pure In 4 Se 3 .