Identification of the Intrinsic Atomic Disorder in ZrNiSn-based Alloys and Their Effects on Thermoelectric Properties

Atomic disorder is common in half-Heusler (HH) compounds, and it significantly affects thermoelectric properties of HH compounds. Despite the rapid development of material characterization methods, the identification of atomic disorder in HH compounds and their correlation with thermoelectric properties remain big challenges. In this work, ZrNiSn HH samples are prepared by levitation melting combined with spark plasma sintering. HAADF-STEM images indicate that two dominant atom disorder, i.e., Ni-interstitial and Zr/Sn atomic disorder, are coexist in ZrNiSn HH compounds. Both the composition deviation and lattice deformation are observed by EPMA and XRD techniques, which is possibly related to these two types of atomic disorder. The degree of atomic disorder could be regulated by the annealing temperature as well as the carrier injection by Ta doping. We find that such atomic disorder can effectively reduce the lattice thermal conductivity and enhance the electrical conductivity. These variations are mainly attributed to alloy scattering and bandgap reduction. This remarkable decoupling of the electronic conductivity and thermal conductivity means that the ZT of a ZrNiSn sample at 923 K improves by 23% due to the increasing of atomic disorder.