Half-Heusler-like compounds with wide continuous compositions and tunable p- to n-type semiconducting thermoelectrics

Abstract

Half-Heusler and full-Heusler compounds were considered as independent phases with a natural composition gap. Here we report the discovery of TiRu1+xSb (x = 0.15 ~ 1.0) solid solution with wide homogeneity range and tunable p- to n-type semiconducting thermoelectrics, which bridges the composition gap between half- and full-Heusler phases. At the high-Ru end, strange glass-like thermal transport behavior with unusually low lattice thermal conductivity (~1.65 Wm−1K−1 at 340 K) is observed for TiRu1.8Sb, being the lowest among reported half-Heusler phases. In the composition range of 0.15 < x < 0.50, TiRu1+xSb shows abnormal semiconducting behaviors because tunning Ru composition results in band structure change and carrier-type variation simultaneously, which seemingly correlates with the localized d electrons. This work reveals the possibility of designing fascinating half-Heusler-like materials by manipulating the tetrahedral site occupancy, and also demonstrates the potential of tuning crystal and electronic structures simultaneously to realize intriguing physical properties.

Discovery of triple half-Heusler Mg2VNi3Sb3 with low thermal conductivity

“…Nb 0.8 CoSb for NbCoSb and TiFe 1.5 Sb 55 in TiFeSb). Examples of such unstable metallic XYZ compositions containing impurity phases are NV = −1 based TiFeSb, 24 ZrRuSb, 25 TiRuSb, 26 HfRuSb 27 and NV = 1 based NbCoSb, 28 NbIrSb. 29 XRD results in ref.…”

High figure-of-merit and power generation in high-entropy GeTe-based thermoelectrics

“…Thermoelectric (TE) technology provides the prospect for harvesting waste heat from scattered heat sources, which suffer from low conversion efficiency ( 5 – 8 ). Conversion efficiency is related primarily to the dimensionless figure-of-merit [ zT = S 2 σ T /(κ e + κ L )] of thermoelectric materials, where S , σ, T , κ e , and κ L denote the Seebeck coefficient, electrical conductivity, absolute temperature, carrier, and lattice thermal conductivities, respectively ( 9 – 12 ). To pursue high TE performance, the electrical and thermal transport properties should be simultaneously decoupled and optimized.…”

Structural Understanding of the Slater–Pauling Electron Count in Defective Heusler Thermoelectric TiFe1.5Sb as a Valence Balanced Semiconductor

“…However, the Ti-interstitial defect in the full-Heusler site is likely to be higher in energy than the Fe-interstitial defect as suggested by the fact that the less electropositive transition metal often occupies the full-Heusler site. Phase diagram studies on the Ti–Fe–Sb system show that Ti substitutes for Fe in the Heusler phase at higher temperatures and electronic structure calculations on isovalent TiRu 1.5 Sb show that the structure is semiconducting as long as every two Fe-atoms are substituted for with one Ti-atom, in line with the expected 4+ nature of the Ti-atom.…”

“…Structures (a) and (b) are 17.3 meV/atom and 76 meV/atom higher than the ground-state R 3 m structure, respectively. These results suggest that the occupancies of the 4c and 4d sites and thereby the electronic properties of Slater–Pauling compositions like TiFe 1.5 Sb (e.g., MRu 1.5+ x Sb − ) could be sensitive to temperature. Experimentally, the Ru occupancies of the 4c and 4d sites in the semiconducting isoelectronic TiRu 1.5 Sb have been probed directly using atom-resolved high-angle annular dark-field (HAADF) images and were found to be unequal, which is in line with our analysis.…”

“…Recently, defective Heuslers TiFe 1.33 Sb, MRu 1.5+ x Sb, − and MCo 1.5 Sn (M = Ti, Zr, and Hf) with interstitial defects on the full-Heusler sites (see Figure ) were reported with very low lattice thermal conductivities (as low as 1.65 W m –1 K –1 at T = 300 K). Similar to most other half-Heuslersdefective or defect-freethese defective compounds also stabilize close to the semiconducting ground-state composition .…”