Experimental revelation of multiband transport in heavily doped BaCd2Sb2 with promising thermoelectric performance

Abstract

Zintl compounds have long been considered as potential thermoelectrics because of the compositional richness that enables a large-scale manipulation on both charge and phonon transport properties. The CaAl2Si2-structured ternary Zintl family with a chemical formula of AB2C2 is particularly interesting for thermoelectric applications in p-type because of its intrinsic low lattice thermal conductivity and its tunable valence band structures. Years of development has led to a realization of thermoelectric figure of merit (zT) of unity or higher in p-type conduction. This work focuses on thermoelectric BaCd2Sb2, a member from this Zintl family that has been rarely investigated. It is revealed that this material shows a sufficiently large band gap of Eg∼0.7eV and an intrinsically low lattice thermal conductivity of 0.6 W/m-K at ∼700 K. Interestingly, a successful doping for increasing the hole concentration by about two orders of magnitude (from ∼6 × 1017 to ∼6 × 1019 cm−3) enables an experimental revelation of charge transport by multiple bands with hole concentrations above 3 × 1019 cm−3. Such a multiband transport and a broad range of hole concentration ensure a superior electronic performance to be achieved, largely contributing to the realization of a zT approaching unity. This work demonstrates BaCd2Sb2 as a novel promising Zintl thermoelectric material.