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In this study, a series of Cu2–x SnSe3 (x = 0.075–0.175) and Cu2Sn1–y Se3 (y = 0.06–0.1) compounds were synthesized by self-propagating high-temperature synthesis combined with plasma-activated sintering. The effects of different cation vacancies (Cu vacancies and Sn vacancies) on the thermoelectric properties are systematically studied. Both Cu vacancies and Sn vacancies enhance the carrier densities and move the Fermi level deeply into the valence band, promoting the multiband from Γ and S points involved in the electrical transport and increasing the effective mass, which is further corroborated by the theoretical calculation. Due to the stronger carrier scattering caused by Cu vacancies, the mobilities of samples with Cu deficiencies reduce leading to decreased power factors. The power factors of samples with Sn deficiencies increase owing to the increased carrier concentration and attaining a maximum power factor of 10.17 μW cm–1 K–2 at 800 K. Besides, the deficiencies of both Cu and Sn strengthen the phonon scattering, and samples with Cu deficiencies obtain lower thermal conductivity than samples with Sn deficiencies due to the lower electronic thermal conductivity. All the samples with cation deficiencies have improved thermoelectric properties. For Cu1.875SnSe3, ZT reaches 0.95 at 800 K, which is 83% higher than those of undoped samples, while for Cu2Sn0.93Se3, ZT reaches 0.87 at 800 K, which is a 67% improvement.

The ZrNiSn alloy, a member of the half-Heusler family of thermoelectric materials, shows great potential for mid-to-high-temperature power generation applications due to its excellent thermoelectric properties, robust mechanical properties, and good thermal stability. The existing synthesis processes of half-Heusler alloys are, however, rather time and energy intensive. In this study, single-phase ZrNiSn bulk materials were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. The analysis of thermodynamic and kinetic processes shows that the SHS reaction in the ternary ZrNiSn alloy is different from the more usual binary systems. It consists of a series of SHS reactions and mass transfers triggered by the SHS fusion of the binary Ni-Sn system that eventually culminates in the formation of single-phase ternary ZrNiSn in a very short time, which reduced the synthesis period from few days to less than an hour. Moreover, the nonequilibrium feature induces Ni interstitials in the structure, which simultaneously enhances the electrical conductivity and decreases the thermal conductivity, which is favorable for thermoelectric properties. The maximum thermoelectric figure of merit ZT of the SHS + SPS-processed ZrNiSnSb alloy reached 0.7 at 870 K. This study opens a new avenue for the fast and low-cost fabrication of half-Heusler thermoelectric materials.

One-step plasma-activated sintering (OS-PAS) fabrication of single-phase high-performance CoSb 3 -based skutterudite thermoelectric material with a hierarchical structure on a time scale of a few minutes is first reported here. The formation mechanism of the CoSb 3 phase and the effects of the current and pressure fields on the phase transformation and microstructure evolution are studied in the one-step PAS process. The application of the panoscopic approach to this system and its effect on the transport properties are investigated. The results show that the hierarchical structure forms during the formation of the skutterudite phase under the effects of both current and sintering pressure. The samples fabricated by the OS-PAS technique have defined hierarchical structures, which scatter phonons more intensely over a broader range of frequencies and significantly reduce the lattice thermal conductivity. High-performance bulk Te-doped skutterudite with the maximum ZT of 1.1 at 820 K for the composition CoSb 2.875 Te 0.125 was obtained. Such high ZT values rival those obtained from single filled skutterudites. This newly developed OS-PAS technique enhances the thermoelectric performance, dramatically shortens the synthesis period and provides a facile method for obtaining hierarchical thermoelectric materials on a large scale. NPG Asia Materials (2017) 9, e352; doi:10.1038/am.2017.1; published online 24 February 2017 INTRODUCTION Thermoelectric technology uses solid-state semiconductors, which can directly convert heat into electricity and vice versa using the Seebeck effect for power generation and Peltier effect for cooling. The efficiency of thermoelectric materials is governed by the dimensionless figure of merit ZT = α 2 σT/κ, where α, σ, T and κ are the Seebeck coefficient, electrical conductivity, absolute temperature and thermal conductivity, respectively. Many studies have been conducted in the past decades 1-5 to enhance the thermoelectric properties with a focus on improving the power factor and decreasing the thermal conductivity. Because of the high electrical transport performance 6,7 and relatively good mechanical properties, 8 skutterudites are considered notably promising for commercial power generation thermoelectric applications 9,10 in the temperature range of 500-900 K. 6,7,11,12 However, the disadvantage of skutterudites is their notably high lattice thermal conductivity of 410 W m − 1 K − 1 . To obtain a higher conversion efficiency, the thermal conductivity must be further reduced.The thermal conductivity of skutterudites derives from the contributions of phonons with a notably broad range of frequencies and mean free paths (MFPs). [13][14][15][16][17] Those phonons are primarily scattered by features in the structure (dopant, nanostructures and so on) that are comparable in size to the MFP of the phonons. For example, the high-frequency (short-wavelength) phonons tend to be scattered more