Suppression of thermal conductivity without impeding electron mobility in n-type XNiSn half-Heusler thermoelectrics

Abstract

Addition of Cu to XNiSn half-Heuslers improves homogeneity and reduces thermal conductivity without affecting electron mobility.

Advances in half-Heusler alloys for thermoelectric power generation

“…63 Similarly Hall data for the Ti 0.5 Zr 0.25 Hf 0.25 NiCu y Sn series conform to m DoS * = 4.1 m e , including the undoped sample. 64 Some data in the Ti 1-x Hf x NiSn 1-y Sb y series also suggests m DoS * = 3.9 m e . 180 While the large m DoS * in the Ti 1-x Ta x Ni 0.92 Sn system was not addressed, first principles calculations on the interstitial Cu-doped materials suggest the appearance of a second conduction band minimum in the electronic bandstructure, supporting the idea that the increase in m DoS * is caused by to an increase in N v .…”

“…Nevertheless, powder-based routes can give good performing samples, but care has to be taken with precursors, and the lower temperatures also place limitations on grain growth. 59,63,64 Other means of achieving reaction include microwave synthesis and self-propagating combustion synthesis. [65][66][67][68][69] After initial reaction it is common to anneal the sample, typically between 900-1000 °C, to equilibrate the sample and increase homogeneity.…”

“…This can be ascribed in large part to low expected diffusion rates of the X IV site atoms, leading to regions with kinetically trapped compositions resulting from the melting stage. 39,168 Interestingly, SEM and SXRD data for Ti 0.5 Zr 0.25 Hf 0.25 NiCu y Sn prepared by a powder route (never exceeding 850 °C) shows an increasing homogenisation on the X IV site with increasing Cu content, 64 which was attributed to the presence of a molten Cu-Sn phase that improves the reaction kinetics during synthesis.…”

“…180 While the large m DoS * in the Ti 1-x Ta x Ni 0.92 Sn system was not addressed, first principles calculations on the interstitial Cu-doped materials suggest the appearance of a second conduction band minimum in the electronic bandstructure, supporting the idea that the increase in m DoS * is caused by to an increase in N v . 64 Given the high volume of publications on the X IV NiSn system, a number of protocols outside of melting, ball-milling and hot-pressing/SPS exist, with TiNiSn being the target of most experimentation. Microwave synthesis has reported for TiNiSn, achieving a peak zT 740 K = 0.45.…”

Atom Probe Tomography of a Cu-Doped TiNiSn Thermoelectric Material: Nanoscale Structure and Optimization of Analysis Conditions

“…Typical compositions are Ti0.5Zr0.25Hf0.25NiSn0.99Sb0.01, where alloying with Ti, Zr and Hf on the X-site is used to embed phonon point-defect scattering and Sb is used as a dopant to achieve the best possible trade-off between S,  and el (Bos, 2021). In a contrasting strategy, small amounts of Cu (0-10% occupancy) on the vacant site in TiNiSn can achieve similar optimisation and leads to promising ZT = 0.6-0.8 at 800 K (Barczak et al, 2018(Barczak et al, , 2019.…”