Compositional Tailoring for Realizing High Thermoelectric Performance in Hafnium-Free n-Type ZrNiSn Half-Heusler Alloys

Abstract

Compositional tailoring enables fine-tuning of thermoelectric (TE) transport parameters by synergistic modulation of electronic and vibrational properties. In the present work, the aspects of compositionally tailored defects have been explored in ZrNiSn-based half-Heusler (HH) TE materials to achieve high TE performance and cost effectiveness in n-type Hffree HH alloys. In off-stoichiometric Ni-rich ZrNi 1+x Sn alloys in a low Ni doping limit (x < 0.1), excess Ni induces defects (Ni/vacancy antisite + interstitials), which tend to cause band structure modification. In addition, the structural similarity of HH and full-Heusler (FH) compounds and formation energetics lead to an intrinsic phase segregation of FH nanoscale precipitates that are coherently dispersed within the ZrNiSn HH matrix as nanoclusters. A consonance was achieved experimentally between these two competing mechanisms for optimal HH composition having both FH precipitates and Ni/vacancy antisite defects in the HH matrix by elevating the sintering temperature up to the solubility limit range of the ZrNiSn system. Defect-mediated optimization of electrical and thermal transport via carrier concentration tuning, energy filtering, and possibly all scale-hierarchical architecture resulted in a maximum ZT ≈ 1.1 at 873 K for the optimized ZrNi 1.03 Sn composition. Our findings highlight the realistic prospect of enhancing TE performance via compositional engineering approach for wide applications of TE.

Advances in half-Heusler alloys for thermoelectric power generation

“…Here, melting is followed by ball milling and rapid consolidation at high temperature and under applied pressure, often using spark plasma sintering (SPS), but no long duration heating is used. 47,48,70,71 This can be a favourable route that maintains embedded nanostructures that would be annealed out at high temperatures. 72 In some instances, most notably for ZrCoBi, the melting step is removed altogether, leading to an efficient synthetic protocol.…”

Self Doping for Synergistically Tuning the Electronic and Thermal Transport Coefficients in n-type Half-Heuslers

“…Nagendra et al achieved zT ≈ 1.1 at 873 K for the optimized ZrNi 1.03 Sn composition. 35 Our first-principles theoretical investigation of the experimental results also showed that self doping of Ni (by 3 %) in ZrNiSn also leads to an unprecedented lowering in the κ L . 40 On the other hand, the same group examined the implication of intrinsic doping and spinodal decomposition on the thermal and electrical transport parameters of nonstoichiometric (Ti, Zr)CoSb HH systems.…”

“…An analysis of change in lattice parameter and space group with doping is given in the supplementary (see SI section S2, Table S1), the lattice parameter is typically found to be increased with doping concentration, which is found to be in agreement with experimental literature. 35,42,58 The stability of these compositions i.e., ZrY 1+m Z (Y = Ni, Pd, Co; Z = Sn, Sb and m = 0, 0.03, 0.125, 0.5, 1) is analyzed by calculating the formation energies using eqn 1.…”

“…25 However, it has been also observed that off-stoichiometric excess elemental doping of these half-Heusler phases also leads to a drastic lowering in the κ L . [33][34][35][36] Douglas et al have studied phase evolution in TiNiSn materials by adding extra Ni (≤ 0.25), leading to the formation of two coexisting phases (half-Heusler-TiNiSn and full Heusler-TiNi 2 Sn) and observed an increase in the value of zT from 0.35 to 0.44 37 at 800K. Similarly, Chai and Kimura also investigated the microstructural evolution of TiNiSn and obtained a large density of nano-sized full-Heusler (FH) precipitates within the half-Heusler matrix in slightly Ni-rich TiNiSn and found an increase in the power factor at high temperatures (∼ 3.5 mWm −1 K −2 compared to ∼ 2.5 mWm −1 K −2 at 700K) for the parent compound TiNiSn.…”

Scalable colloidal synthesis of Bi2Te2.7Se0.3 plate-like particles give access to a high-performing n-type thermoelectric material for low temperature application

“…The calculated CF of our TE material decreases with increasing temperature as a result of its direct correlation with ZT, and it is comparable to other state-of-the-art n-type TE materials in mid-temperature range. 69 This result suggests that n-type BTS consolidated from plate-like particles will also be a suitable TE material for segmentation with high-performance mid-temperature TE materials 22 , such as PbTe 70 and half-Heuslers, [71][72][73][74] for achieving efficient TE energy conversion. commercial applications, zone melting is a commonly used production technology for Bi2Te3based materials and devices.…”