Effects of yttrium doping on the thermoelectric properties of Hf 0.6 Zr 0.4 NiSn 0.98 Sb 0.02 half-Heusler alloys A Heusler Fe 2 V 1-x W x Al sintered alloy was synthesized to evaluate the effect of W substitution on thermoelectric properties of the Heusler alloy. The Seebeck coefficient and the electrical conductivity are simultaneously enhanced through electron injection resulting from the W substitution. Comparison with the Si-substituted Fe 2 VAl alloy reveals that the additional electronic states derived from W 5d orbital in the vicinity of pseudogap are likely to degrade the Seebeck coefficient. Thermal conductivity is effectively reduced by the W substitution because of the large atomic mass and volume of W compared to the constituent elements of Fe 2 VAl alloy. The appreciable reduction of thermal conductivity, without a serious deterioration in electrical conduction, enhances the thermoelectric figure of merit in the Heusler alloy. V C 2012 American Institute of Physics.

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Polycrystalline samples in the series Ti1-xTaxS2 with x varying from 0 to 1 were prepared using solid-liquid-vapor reaction and spark plasma sintering. Rietveld refinements of X-ray diffraction data are consistent with the existence of a full solid solution for x ≤ 0.4. Transport measurements reveal that tantalum can act as electron donor when substituted in the Ti sites. As a consequence, the electrical resistivity and the absolute value of the Seebeck coefficient decrease with Ta content due to an increase in the carrier concentration. The lattice thermal conductivity being reduced due to mass fluctuation effect, the ZT values in Ti0.95Ta0.05S2 is slightly increased as compared to TiS2.

Nanoscale constituents in bulk materials can promote enhanced boundary-scattering in the transport of phonons as well as electrons, which is considered a key design factor for enhancing thermoelectric properties. Here, we demonstrate a method for synthesizing zinc oxide bulk materials from nanoparticles without significant grain growth by means of pressure-induced deformation at 200°C. This allows us to comprehensively analyze the grain size dependence of thermoelectric properties in the nanoscale range above 30 nm, the size of a nanoparticle. Grain size was found to largely influence thermal conductivity as well as electrical conductivity. The observed thermal conductivity agreed with the Callaway model, indicating that enhanced phonon boundary-scattering was responsible for the variation. On the contrary, Seebeck coefficient was mostly governed by effective mass and carrier concentration, and was independent of the grain size. The dimensionless figure of merit systematically increased with grain size, which challenged the effect of nanograin on this system.

Nanosize particles of aluminum nitride have been successfully synthesized by a pulsed wire discharge (PWD). Intense pulsed current through an aluminum wire evaporated the wire to produce a high‐density plasma. The plasma was then cooled by an ambient gas mixture of NH3/N2, resulting in nitridation. As a result, nanosize particles of aluminum nitride were formed. The average particle diameter was found to be ∼28 nm with a geometric standard deviation of 1.29. The maximum AlN content of 97% in the powders was achieved by optimizing various parameters: the gas pressure, the ratio of NH3 and N2, the wire diameter, the pulse width, and the input electrical energy. The ratio of the AlN powder production to the electrical energy consumption was evaluated as ∼40 g/(kW·h). Thus, PWD is a very efficient and promising method to synthesize nanosize powders of AlN.