Alloying for orbital alignment enables thermoelectric enhancement of EuCd2Sb2
Abstract
Alignment of doubly degenerate pxy and nondegenerate pz band orbitals at the Γ point in the Brillouin zone for high orbital degeneracy has been demonstrated as an effective strategy for advancing thermoelectric AB2C2 Zintl compounds in p-type conduction. Formation of solid solutions of different compounds with opposite energy offsets between pxy and pz orbitals would enable a minimization of energy offset to realize an orbital alignment, and thereby lead to an enhanced electronic performance. Here we show that alloying EuCd2Sb2 with EuZn2Sb2 not only effectively aligns the pxy and pz valence bands for superior electronic performance, but also significantly reduces the lattice thermal conductivity resulting from the phonon scattering by alloy defects. Eventually, the average thermoelectric figure of merit (zT) of the EuCd1.4Zn0.6Sb2 alloy is enhanced by at least 35% compared to that of pristine EuCd2Sb2 and the alloying agent EuZn2Sb2, demonstrating that this alloy is a promising thermoelectric material.