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In thermoelectric (TE) generators, maximizing the efficiency of conversion of direct heat to electricity requires the reduction of any thermal and electrical contact resistances between the TE legs and the metallic contacts. This requirement is especially challenging in the development of intermediate to high-temperature TE generators. PbTe-based TE materials are known to be highly efficient up to temperatures of around 500 °C; however, only a few practical TE generators based on these materials are currently commercially available. One reason for that is the insufficient bonding techniques between the TE legs and the hot-side metallic contacts. The current research is focused on the interaction between cobalt-metallized n-type 9.104 × 10−3 mol % PbI2-doped PbTe TE legs and the Ag0.32Cu0.43In0.25 brazing alloy, which is free of volatile species. Clear and fine interfaces without any noticeable formation of adverse brittle intermetallic compounds were observed following prolonged thermal treatment testing. Moreover, a reasonable electrical contact resistance of ~2.25 mΩmm2 was observed upon brazing at 600 °C, highlighting the potential of such contacts while developing practical PbTe-based TE generators. [ABSTRACT FROM AUTHOR]

The search for alternative energy sources is presently at the forefront of applied research. In this context, thermoelectricity for direct energy conversion from thermal to electrical energy plays an important role. This paper is concerned with the development of highly efficient p-type GePbTe alloys for thermoelectric applications, using spark plasma sintering. The carrier concentration of GeTe was varied by alloying of PbTe and/or by BiTe doping. Very high ZT values up to ~1.8 at 500°C were obtained by doping PbGeTe with 3 mol% BiTe. [ABSTRACT FROM AUTHOR]

Thermoelectrics is a renewable energy method, capable of a direct conversion of waste heat into useful electricity, which can be applied for tackling global warming, high pollution levels and dilution of fossil energy sources. For this purpose novel and highly efficient thermoelectric compositions should be developed and analyzed under practical operation conditions. In the current research the effects of grain size and thermal treatment under operation conditions on the thermoelectric performance of Ge 0.962 Bi 0.038 Te 1.057 were investigated. Following hot-pressing both positive electronic and lattice effects were identified for sub-micron grained samples, enabling very high figure of merit, ZT , values of up to 1.8. These values were slightly degraded down to ≈ 1.4 following thermal treatment, mainly due to grain coarsening, highlighting the requirement of grain growth inhibition for maximizing the potential of this composition. • Nano-grained Ge 0.962 Bi 0.038 Te 1.057 was found to exhibit a very high ZT of 1.8 following hot-pressing. • This impressing ZT was attributed to both enhanced phonon scattering and electronic donor states at grain boundaries. • Reduction of ZT to 1.4 was noticed after thermal treatment, highlighting the requirement of grain growth inhibition [ABSTRACT FROM AUTHOR]

Mechanical alloying synthesis was applied on the thermoelectric half-Heusler materials in order to explore the potential of such scalable synthesis method in this family of compounds. (Hf,Ti)Co(Sb,Sn) solid solutions were prepared by mechanical alloying followed by hot pressing and their thermoelectric properties were studied in the temperature range of 300–980 K. After successful synthesis, two different methods were applied to enhance the thermoelectric performance of p-type (Hf,Ti)Co(Sb,Sn) materials: (a) adjustment of the Ti/Hf ratio and (b) fine tuning of carrier concentration by the substitution of Sb with Sn. The isoelectronic substitution of Ti with Hf led to an important reduction in the lattice thermal conductivity and a high ZT of 0.84 at 980 K for Hf 0.6 Ti 0.4 CoSb 0.8 Sn 0.2. The effect of charge carrier concentration was investigated by preparing Hf 0.6 Ti 0.4 CoSb 1−y Sn y (0.15, 0.17, 0.20, 0.23, 0.25) compounds, using different mechanical alloying durations. The Hf 0.6 Ti 0.4 CoSb 0.83 Sn 0.17 composition, prepared by 4 h ball-milling, reached an impressive ZT ~1.1 at 973 K. • Half-Heusler solid solutions were synthesized via mechanical alloying as single phases. • Hf 1−x Ti x CoSb 0.80 Sn 0.20 and Hf 0.6 Ti 0.4 CoSb 1−y Sn y series were studied. • The Hf 0.6 Ti 0.4 CoSb 0.83 Sn 0.17 composition reached the maximum ZT of 1.1 at 973 K. [ABSTRACT FROM AUTHOR]