Development of Thermoelectric Half-Heusler Alloys over the Past 25 Years

Abstract

Half-Heusler alloys are among the most promising thermoelectric materials. In the present review, thermoelectric properties (at 300 K and 800 K) of more than 1100 compositions from more than 220 publications between 1998 and 2023 were collected and evaluated. The dependence of the peak figure of merit, ZTmax, of p- and n-type half-Heusler alloys on the publishing year and the peak temperature is displayed in several figures. Furthermore, plots of ZT vs. the electrical resistivity, the Seebeck coefficient and the thermal conductivity at 300 K and 800 K are shown and discussed. Especially thermal conductivity vs. power factor leads to a good overview of ZT. For both p- and n-type individually separated into systems, ZTs and peak ZTs in dependence on the composition are displayed and discussed. This overview can help to find the ideal half-Heusler alloy for practical use.

Achieving Compatible p/n-Type Half-Heusler Compositions in Valence Balanced/Unbalanced Mg1–xVxNiSb

“…Fabrication of the Thermoelectric Module with p-and n-Type Mg 1−x V x NiSb. Despite the low thermoelectric performance of Mg 1−x V x NiSb compared to conventional highperformance HH materials, for example, ZrNiSn zT > 1.4 at 873 K, 16 Ti 0.5 Zr 0.25 Hf 0.25 NiSn with zT > 1.5 at 825 K, 43 and others, 4 the advantage of obtaining both p-and n-type materials from the same parent compound makes Mg 1−x V x NiSb compositions more prominent for the fabrication of thermoelectric modules. For example, the difference of the coefficient of linear thermal expansion (CTE) between pand n-type legs can be minimized.…”

“…HH compounds are promising materials for mid-to high-temperature thermo-electric applications because of their high power factor (PF), mechanical durability, and thermal stability. [1][2][3][4]17 Nevertheless, the high lattice thermal conductivity κ L ∼15−20 W m −1 K −1 of HHs 1−4 severely restricts their thermoelectric performance. Alloying and nanostructuring are common strategies to improve the thermoelectric properties by lowering the κ L of the material with enhanced phonon scattering.…”

“…Half-Heusler (HH, general formula: XYZ, with X and Y being mainly transition metal elements and Z being an element from the third to sixth main group) materials have been studied extensively for their possible use in thermoelectrics, spintronics, and magnetic applications. Compositional diversity allows for more freedom in tuning electronic and phonon structures, which is useful for altering thermoelectric properties. − As a result, the short-range/long-range ordering, disorders, and other defects have been investigated in HH compounds. − Common ternary HH phases are semiconductors with valence balanced compositions that stabilize the crystal structure at a specific number of electrons (e.g., valence electron count (VEC) of 18) in the valence shell, as determined by the 18-electron rule. − In a broader sense, these semiconducting mixtures comprised of rare-earth-based compounds can also stabilize as higher VEC systems (e.g., the 27-electron DyNiSb HH). Both 18 VEC (e.g., ZrNiSn) as well as 27 VEC (e.g., DyNiSb) are valence balanced compositions, i.e., net valence (NV) = 0; ZrNiSn (NV = 4 (Zr 4+ s 0 d 0 ) + 0 (Ni 4+ d 10 ) – 4­(Sn 4– s 2 p 6 )) as well as DyNiSb (NV = 3 (Dy 3+ s 0 d 0 ) + 0 (Ni 4+ d 10 ) – 3­(Sb 3– s 2 p 6 )).…”

“…Both 18 VEC (e.g., ZrNiSn) as well as 27 VEC (e.g., DyNiSb) are valence balanced compositions, i.e., net valence (NV) = 0; ZrNiSn (NV = 4 (Zr 4+ s 0 d 0 ) + 0 (Ni 4+ d 10 ) – 4­(Sn 4– s 2 p 6 )) as well as DyNiSb (NV = 3 (Dy 3+ s 0 d 0 ) + 0 (Ni 4+ d 10 ) – 3­(Sb 3– s 2 p 6 )). HH compounds are promising materials for mid- to high-temperature thermoelectric applications because of their high power factor (PF), mechanical durability, and thermal stability. − , Nevertheless, the high lattice thermal conductivity κ L ∼15–20 W m –1 K –1 of HHs − severely restricts their thermoelectric performance. Alloying and nanostructuring are common strategies to improve the thermoelectric properties by lowering the κ L of the material with enhanced phonon scattering. − …”

Structure and Thermoelectric Properties of Mg1–xTixNiSb Quaternary Half-Heusler Alloys

“…Half-Heusler (HH) alloys hold broad application prospects in various fields, including thermoelectrics, spintronics, topological insulators, and semiconductor thin films . In recent years, HH alloys have garnered growing interest, particularly as viable candidates for medium- to high-temperature thermoelectric applications, owing to their exceptional attributes including remarkable thermal stability, mechanical properties, and electrical properties .…”