Double Half-Heuslers

Abstract

Despite decades of research on half-Heusler thermoelectrics, they are predominantly investigated as ternary compounds. From the same chemical phase space, we explore an enormous class of double half-Heuslers based on aliovalent substitution with ordered ground states. These compounds are constrained via crystal chemistry to exhibit much lower thermal conductivities (k L ) relative to the well-known ternary compounds. Additional avenues for k L reduction via alloying with their ''defective'' ternary components emerge that significantly advance the search for high-performance thermoelectric half-Heuslers.

Enhanced Thermoelectric Properties in p‐Type Double Half‐Heusler Ti2−yHfyFeNiSb2−xSnx Compounds

“…The standard diffraction peaks of Ti(Fe 0.5 Ni 0.5 )Sb slightly deviate from that of TiCoSb, which may be due to the lattice distortion caused by Fe and Ni atoms in the Co site. In addition, no observation of additional superlattice diffraction lines related to the Fe and Ni ordering indicates that Fe and Ni atoms are randomly distributed . The diffraction peaks of Ti 2− y Hf y FeNiSb 1.7 Sn 0.3 gradually shift to lower angles as the substituted Hf content increases because of the larger atomic radius of Hf than that of Ti .…”

“…The difference is that Fe atoms and Ni atoms occupy the position of Co atoms in a ratio of 1:1 in Ti 2 FeNiSb 2 . The Fe/Ni disordered scattering makes Ti 2 FeNiSb 2 having much lower intrinsic lattice thermal conductivity than that of TiCoSb …”

“…Following the applications of half‐Heusler compounds with nominal 17‐ and 19‐electron in the field of thermoelectrics, Snyder and co‐workers recently proposed the concept of double half‐Heusler . Taking Ti 2 FeNiSb 2 as an example, it can be regarded as a combination of 17‐electron TiFeSb and 19‐electron TiNiSb .…”

“…Taking Ti 2 FeNiSb 2 as an example, it can be regarded as a combination of 17‐electron TiFeSb and 19‐electron TiNiSb . The quaternary compounds based on the aliovalent substitution have a lower intrinsic thermal conductivity due to the smaller group velocity phonons and the disordered scattering . Although double half‐Heusler compounds have lower intrinsic lattice thermal conductivity, the electrical properties are extremely poor.…”

Machine Learning Chemical Guidelines for Engineering Electronic Structures in Half-Heusler Thermoelectric Materials

“…Conversely, in the Fe-substituted analog, the L-pocket dominates; TiFeSb has 17 valence electrons and a smaller difference in valence. While TiNiSb and TiFeSb are not stable themselves, there are implications for forming solid solutions between TiCoSb and either of the metallic end-members (electronic doping) [29]-the relative energies of the Γand L-points may change.…”