Synergistic effects of Lanthanum substitution on enhancing the thermoelectric properties of β-Zn4Sb3

A core challenge of thermoelectric research is decoupling the otherwise inversely interdependent properties electrical conductivity, thermopower, and lattice thermal conductivity offering synergistic effects. Herein, we present a systematic study in which we have substituted Lanthanum into the Zn-site in β-Zn4Sb3 compound. We observed that La-substitution not only simultaneously enhances electrical conductivity and thermopower over a wide temperature range but also substantially reduces the lattice thermal conductivity. These synergistic effects of La-substitution are discussed in terms of the substitution-induced variation in carrier concentration and effective mass as well as stronger phonon scattering by point defects. As a result, a ∼30% increase of the power factor and a ∼23% reduction in the lattice thermal conductivity led to a state-of-the-art ZT ∼1.3 at 648 K for the bulk sample of β-La0.01Zn3.99Sb3.