Thermoelectric properties of EuZn2Sb2 Zintl compounds: zT enhancement through Yb substitution for Eu

Abstract A Zn 2 Sb 2 ( A : Ca, Sr, Eu, Yb) Zintl compounds have shown excellent thermoelectric performance peaking around 700 K. Among these materials, EuZn 2 Sb 2 and YbZn 2 Sb 2 compounds have the highest carrier mobility, making them particularly interesting. We present the thermoelectric properties of Eu δ Zn 2 Sb 2 (δ = 0.9, 1.0, 1.1) and Eu 1- x Yb x Zn 2 Sb 2 compounds ( x  = 0, 0.1, 0.25, 0.5, 0.75, 1) from 373 to 773 K. Our interest is in studying whether introducing A -site vacancies increases the hole carrier concentration with decreasing Eu content or with increasing Yb substitution, which could lead to optimized power factor at high temperatures. The electrical conductivity showed a non-monotonic change caused by carrier mobility scattering. The thermal conductivity decreased through deviation of the Eu content and through Eu-Yb substitution; in particular, the phonon contribution at 773 K reduced gradually from 1.1 W m −1  K −1 ( x  = 0) to 0.42 W m −1  K −1 ( x  = 1.0) with increasing Yb fraction and reached the predicted minimum lattice thermal conductivity. The dimensionless figure of merit increased from 0.58 to 0.68 at 773 K through a 10% Yb substitution, i.e . Eu 0.9 Yb 0.1 Zn 2 Sb 2 , mainly due to the reduction of phonon thermal conductivity without lowering the power factor.