Electronic scattering in half-Heusler thermoelectrics from resistivity data

Abstract

A key part of optimising thermoelectric materials is understanding the electronic scattering mechanism. For half-Heusler thermoelectrics, the dominant mechanisms are acoustic phonon scattering in pure systems and alloy scattering in highly alloyed systems. In this report, the significance of the residual resistivity ρ0 is highlighted. Large ρ0 values can lead to misidentification of the dominant scattering mechanism when only high-temperature ρ(T) data is available. A straightforward approach to analyse ρ(T) is proposed and applied to a range of HH systems. This reveals large levels of structural disorder in XIVNiSn, whilst XVFeSb has the strongest coupling with acoustic phonons. The electronic scattering mechanism depends sensitively on composition, with acoustic (∝T1.5), metallic (∝T1) and alloy (∝T0.5) scattering observed within the main families of half-Heusler compounds. With the aid of velocity of sound, band mass and carrier concentration data, the deformation potential can be obtained, enabling quantification of the interaction between phonons and carriers, from fits to resistivity data. This work provides a route for the analysis of experimental ρ(T) data that can be applied to a range of thermoelectric materials.

Mechanistic Insights into the Formation of Thermoelectric TiNiSn from In Situ Neutron Powder Diffraction

“…Analysis of transport data has suggested that there is metal-like electronic conduction through the impurity band in addition to the regular valence and conduction bands . In order to accommodate these two conduction channels, σ( T ) was fitted using a parallel degenerate (σ deg , metal-like) and semiconducting (σ int ) channel σ = σ deg + σ int = ( ρ 0 + A T 1.5 ) − 1 + B e false( prefix− E g / 2 k normalB T false) Here, the T 1.5 temperature dependence is typical for acoustic phonon scattering and ρ 0 is the residual electrical resistivity at 0 K. The intrinsic term does not explicitly consider the high mobility ratio, but this minimal model provides a good fit to the data. The final fit parameters are given in Table , and the quality of the fit can be inspected in Figure a.…”

“…Analysis of transport data has suggested that there is metallike electronic conduction through the impurity band in addition to the regular valence and conduction bands. 58 In order to accommodate these two conduction channels, σ(T) was fitted using a parallel degenerate (σ deg , metal-like) and semiconducting (σ int ) channel 62 AT Be ( )…”

Recent progress in phosphide materials for thermoelectric conversion

“…At this point it is unclear if acoustic phonon scattering is indeed the dominant scattering mechanism, with optical phonon and ionised impurity scattering also likely to contribute, but the obtained values of E def are fairly large for thermoelectric materials. 28,[127][128][129] Further work on understanding electronic transport (carrier scattering) in these materials is needed and can provide avenues for further materials discovery and optimisation.…”

“…There continues to be a need for improved thermoelectric materials, based on sustainable large power factors (S 2 σ) but their overall zT continues to be limited by large intrinsic thermal conductivity. 27,28 There is considerable interest in Zintl thermoelectrics based on Sb, with antimonide skutterudites reported with large S 2 σ and zT [29][30][31][32][33] and more recently Mg 3 Sb 2 phases with high zT near room temperature in n-type samples. [34][35][36][37][38] There are several excellent reviews and book chapters covering Sb-based thermoelectrics, [39][40][41][42][43][44] which support very good zT values, often substantially exceeding unity.…”

“…26 Half-Heuslers boast large power factors ( S 2 σ ) but their overall zT continues to be limited by large intrinsic thermal conductivity. 27,28…”