Effects of Lanthanum Substitution on Thermoelectric Properties of YbZn2Sb2

La x Yb1−x Zn2Sb2 polycrystalline are prepared by solid-state reaction followed by spark plasma sintering. The effect of La substitution on the thermoelectric properties of La x Yb1−x Zn2Sb2 has been investigated. It is found that the substitution of La for Yb donates extra electrons to compensate for the vacancies and produces point defects to scatter phonons, leading to a significant reduction of the lattice thermal conductivity. As a result, a maximum ZT of 0.4 is obtained at x = 0.01, 18% enhancement in contrast to that of a pure sample as a result of the identical electrical properties and the largely reduced thermal conductivity.