Efficient interlayer charge release for high-performance layered thermoelectrics

Many layered superlattice materials intrinsically possess large Seebeck coefficient and low lattice thermal conductivity, but poor electrical conductivity because of the interlayer transport barrier for charges, which has become a stumbling block for achieving high thermoelectric performance. Herein, taking BiCuSeO superlattice as an example, it is demonstrated that efficient interlayer charge release can increase carrier concentration, thereby activating multiple Fermi pockets through Bi/Cu dual vacancies and Pb codoping. Experimental results reveal that the extrinsic charges, which are introduced by Pb and initially trapped in the charge-reservoir [Bi2O2]2+ sublayers, are effectively released into [Cu2Se2]2− sublayers via the channels bridged by Bi/Cu dual vacancies. This efficient interlayer charge release endows dual-vacancy- and Pb-codoped BiCuSeO with increased carrier concentration and electrical conductivity. Moreover, with increasing carrier concentration, the Fermi level is pushed down, activating multiple converged valence bands, which helps to maintain a relatively high Seebeck coefficient and yield an enhanced power factor. As a result, a high ZT value of ∼1.4 is achieved at 823 K in codoped Bi0.90Pb0.06Cu0.96SeO, which is superior to that of pristine BiCuSeO and solely doped samples. The present findings provide prospective insights into the exploration of high-performance thermoelectric materials and the underlying transport physics.

Thermoelectric Properties of Half-Heusler Compounds N-type MNiSn and P-type MPtSn (M = Hf, Zr)

To design and to develop Half-Heusler based high-temperature thermoelectric materials, thermoelectric properties of n-type MNiSn and p-type MPtSn (M = Hf, Zr) were investigated based on two respective strategies. For the n-type (Hf, Zr)NiSn, a combined process of optical floating zone melting and hot-pressing was applied aiming to reduce thermal conduction through the lattice contribution. For the p-type HfPtSn, power factor and hence figure of merit ZT were dramatically improved by the p-type doping of Ir and Co targeting for Pt-site, which effectively lower electrical resistivity. The additions of Ir and Co are expected not only to increase carrier concentration but also to suppress the lattice thermal conduction by substituting for Pt.