High Thermoelectric Performance in n-Type Degenerate ZrNiSn-Based Half-Heusler Alloys Driven by Enhanced Weighted Mobility and Lattice Anharmonicity

Abstract

ZrNiSn-based half-Heusler (HH) alloys are well-established alloys for n-type mid-temperature thermoelectric applications because of their chemical and thermal stability and narrow band gap driven semiconducting behavior. Here, we observed a high figure of merit, ZT ∼ 1, at 873 K in aliovalent Nb-doped composition Zr1–x Nb x NiSn (x = 0–0.035) for x = 0.03 HH alloy prepared by employing a combination of arc-melting and spark plasma sintering. The high figure of merit is attributed to synergistic enhancement of the power factor with thermal conductivity reduction. Further, the enhancement of the power factor is correlated with the improved weighted mobility and reduction in thermal conductivity is analyzed in the framework of the model based on the theories of Callaway, Slack, and Abeles. The results are corroborated theoretically to establish the efficacy of Nb doping in ZrNiSn within semimetallic regimes for ZT enhancement. The synthesized Hf-free HH alloys establish Nb as an effective dopant for attaining high-ZT and cost-efficient HH-based n-type TE material in a mid-temperature regime for power generation application.

Low Lattice Thermal Conductivity in a Wider Temperature Range for Biphasic-Quaternary (Ti,V)CoSb Half-Heusler Alloys

“…S holds an inverse relationship with σ and increases with increasing temperature. To understand the degenerate electrical transport of the synthesized Ti 1– x V x CoSb HH alloys (0.25 < x < 1), we estimated the carrier effective mass ( m *) based on energy-independent relaxation time approximation, assuming a single parabolic band using the Pisarenko relationship between S and n , which is expressed as S = (8π 2 k B 2 /3 eh 2 ) m * T (π/3 n ) 2/3 , wherein k B and h are the Boltzmann constant and Planck’s constant, respectively. , The evaluated m * (Table ) follows TiCoSb < (Ti, V)­CoSb < VCoSb, where m e represents the mass of an electron, suggesting an increased effective mass with the VEC increase of the HH composition. A higher S was measured for annealed Ti 0.5 V 0.5 CoSb HH alloys, which can be ascribed to reduced n H and increased m * upon annealing due to the occurrence of spinodal decomposition.…”

Reduced Lattice Thermal Conductivity for Half-Heusler ZrNiSn through Cryogenic Mechanical Alloying

“…Temperature dependence of (a) electrical conductivity, (b) Seebeck coefficient, (c) Pisarenko plot at 50 °C, (d) PF, (e) total thermal conductivity, (f) electrical thermal conductivity, (g) lattice thermal conductivity, and (h) TE figure of merit ( zT ) of ZrNiSn compounds. Total and lattice thermal conductivities and zT values of some other studies (ref : levitation melting followed by 10 h planetary BM; ref : AM followed by 6 h planetary BM; ref : levitation melting followed by melt spinning in argon; ref : AM followed by SPS; and ref : AM followed by annealing in 900 °C for 168 h and SPS) are presented for comparison. ,,,, …”

A mechanistic view of defect engineered VFeSb half-Heusler alloys

“…[17][18][19][20][21][22][23] This is due to the remarkable electronic transport with high power factors exhibited by many of these 18 VEC alloys, which desirably can be formed with constituents within the realm of earth-abundant materials. [24][25][26][27][28][29][30][31] Having a ternary equiatomic XYZ composition, most HH alloys crystallize into a cubic crystal system [space group F% 43m (no. 216)] and host a rich variety of 3d, 4d, and 5d transition metal elements.…”