Thermoelectric properties of the half-Heusler phase ScNiSb (space group F $\overline{4}$ 3m) were studied on a polycrystalline single-phase sample obtained by arc-melting and spark-plasma-sintering techniques. Measurements of the thermopower, electrical resistivity, and thermal conductivity were performed in the wide temperature range 2–950 K. The material appeared as a p-type conductor, with a fairly large, positive Seebeck coefficient of about 240 μV K⁻¹ near 450 K. Nevertheless, the measured electrical resistivity values were relatively high (83 μΩm at 350 K), resulting in a rather small magnitude of the power factor (less than 1 × 10⁻³ W m⁻¹ K⁻²) in the temperature range examined. Furthermore, the thermal conductivity was high, with a local minimum of about 6 W m⁻¹ K⁻¹ occurring near 600 K. As a result, the dimensionless thermoelectric figure of merit showed a maximum of 0.1 at 810 K. This work suggests that ScNiSb could be a promising base compound for obtaining thermoelectric materials for energy conversion at high temperatures.

Deeper understanding of electrical and thermal transport is critical for further development of thermoelectric materials. Here we describe the thermoelectric performance of a group of rare-earth-bearing half-Heusler phases determined in a wide temperature range. Polycrystalline samples of $\mathrm{Sc}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Dy}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Er}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$, and $\mathrm{Lu}\mathrm{Ni}\mathrm{Sb}$ are synthesized by arc melting and densified by spark plasma sintering. They are characterized by powder x-ray diffraction and scanning electron microscopy. The physical properties are studied by means of heat-capacity and Hall-effect measurements performed in the temperature range from 2 to 300 K, as well as electrical-resistivity, Seebeck-coefficient, and thermal-conductivity measurements performed in the temperature range from 2 to 950 K. All the materials except $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$ are found to be narrow-gap intrinsic $p$-type semiconductors with rather light charge carriers. In $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$, the presence of heavy holes with large weighted mobility is evidenced by the highest power factor among the series ($17\mu \mathrm{W}{\mathrm{K}}^{-2}{\mathrm{cm}}^{-1}$ at 700 K). The experimental electronic relaxation time calculated with the parabolic band formalism is found to range from $0.8\times {10}^{-14}$ to $2.8\times {10}^{-14}$ s. In all the materials studied, the thermal conductivity is between 3 and $6{\mathrm{W\; m}}^{-1}{\mathrm{K}}^{-1}$ near room temperature (i.e., smaller than in other pristine $d$-electron half-Heusler phases reported in the literature). The experimental observation of the reduced thermal conductivity appears fully consistent with the estimated low sound velocity as well as strong point-defect scattering revealed by Debye-Callaway modeling. Furthermore, analysis of the bipolar contribution to the measured thermal conductivity yields abnormally large differences between the mobilities of $n$-type and $p$-type carriers. The latter feature makes the compounds examined excellent candidates for further optimization of their thermoelectric performance via electron doping.

The solid-state reaction of WO₃ with W was studied in order to clarify the phase formation in the binary system W-O around the composition WO_x (2.50 ≤ x ≤ 3) during spark plasma sintering (SPS). A new phase “WO_2.82” is observed in the range 2.72 ≤ x ≤ 2.90 which might have the composition W₁₂O₃₄. The influence of the composition on the thermoelectric properties was investigated for 2.72 ≤ x ≤ 3. The Seebeck coefficient, electrical conductivity and electronic thermal conductivity are continuously tunable with the oxygen-to-tungsten ratio. The phase formation mainly affects the lattice thermal conductivity κ_lat which is significantly reduced until 700 K for the sample with the composition x = 2.84, which contains the phases W₁₈O₄₉ and “WO_2.82”. In single-phase WO_2.90 and multi-phase WO_x materials (2.90 ≤ x ≤ 3), which contain crystallographic shear plane phases, a similar reduced κ_lat is observed only below 560 K and 550 K, respectively. Therefore, the composition range x < 2.90 in which the pentagonal column structural motif is formed might be more suitable for decreasing the lattice thermal conductivity at high temperatures.

Antiferromagnets are normally thought of as materials with compensated magnetic sublattices. This adds to their technological advantages but complicates readout of the antiferromagnetic state. We demonstrate theoretically the existence of a Dzyaloshinskii-Moriya interaction (DMI), which is determined by the magnetic symmetry classes of ${\mathrm{Cr}}_2{\mathrm{O}}_3$ surfaces with an in-plane magnetic easy axis. The DMI explains a previously predicted out-of-plane magnetization at the nominally compensated surfaces of chromia, leading to a surface-localized canted ferrimagnetism. This is in agreement with magnetotransport measurements and with density functional theory predictions that further allow us to quantify the strength of DMI. The temperature dependence of the transversal resistance for these planes shows distinct behavior in comparison with that of the ${\mathrm{Cr}}_2{\mathrm{O}}_3$ $c$ plane, which we attribute to the influence of DMI. Our Letter provides a framework to analyze surface-driven phenomena in antiferromagnets, and motivates the use of nominally compensated chromia surfaces for antiferromagnetic spintronics and magnonics.

This report presents studies of crystal structures of α- and β-In ₂ S ₃ as well as a mechanism of the 1st order α–β phase transition. The structural part is supported by an analysis of thermoelectric properties and by DFT calculations.