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Thermoelectric generators (TEGs) are devices capable of transforming heat energy into electricity and vice versa. Although TEGs are known and have been in use for around five decades, they are implemented in only a limited range of applications, mainly extraterrestrial applications. This is due to their low technical readiness level (TRL) for widespread use, which is only at levels of 3–5 approaching laboratory prototypes. One of the most setbacks in reaching higher TRL is the lack of understanding of the mechanical and thermo-mechanical properties of TE materials. Out of ~105,000 entries about TE materials only ~100 entries deal with mechanical properties, while only 3 deal with thermo-mechanical properties. GeTe-based alloys with varying other elements, forming efficient p-type thermoelectric materials in the 200 ÷ 500 °C temperature range, have been intensively researched since the 1960s and have been successfully applied in practical TEGs. Yet, their temperature-dependent mechanical properties were never reported, preventing the fulfillment of their potential in a wide variety of practical applications. The combined effects of temperature and mechanical compression of GeTe were explored in the current research by implementing novel quantitative crystallographic methods to statistically describe dislocation activity and modification of the micro-texture as inflecting by the testing conditions. It is suggested, through utilizing these methods, that the combined effect of compression and temperature leads to the dissolving of twin boundaries, which increases dislocation mobility and results in a brittle-to-ductile transition at ~0.45 of the homologous temperature. [ABSTRACT FROM AUTHOR]

Most of the recent methods for thermoelectric (TE) enhancement are focused on reduction of the lattice thermal conductivity values, with an only limited success on efficiency enhancement due to an improved electronic doping action. This is attributed partly to the correlation between the involved electronic properties, contradicting each other in terms of the TE efficiency, and partly to the difficulty of effectively doping such alloys in the optimal 1019 cm−3 carrier concentration range. Even a positive application of an optimal electronic doping level usually results in a narrow maximal figure of merit (ZT) values range, which is followed by an onset of an intrinsic conduction, degrading these values at higher temperatures. Here, a novel BiTe‐ and Cu‐co‐doping of GeTe is reported. Incorporation of Cu electron donors into GeTe–BiTe vacancies results in an effective compensation of the inherent high holes' concentration of GeTe toward the optimal range with pronounced carriers scattering mechanism of ionized impurities, in addition to the known acoustic phonons mechanism, while enhancing of Seebeck coefficient. Adverse high temperature intrinsic conduction effects are suppressed by the rhombohedral‐to‐cubic phase transition of GeTe, extending the maximal ZTs range of ≈1.55 ± 0.1 over a large temperature range. [ABSTRACT FROM AUTHOR]

In an attempt to enhance the thermal to electrical conversion efficiency, novel complicated thermoelectric alloys are constantly reported. Most of these reports, correlate the low lattice thermal conductivity values, attributing to the enhanced efficiencies, to nanofeatures apparent in their systems. Yet, since most of the highly efficient thermoelectric materials ever reported are based on complicated alloys, a major reduction of the lattice thermal conductivity can be solely attributed to alloying/disordering effects. The current manuscript, explores by combined experimental and theoretical, using density functional theory and analytical modeling, approaches the lattice thermal conductivity values originated solely by alloying/disordering effects in the highly thermoelectrically efficient p-type Ge xPb1- xTe alloys. By comparing these calculated results to various reported experimental values following different synthesis routes, it is shown that solution-treated samples fit well to the calculated values while for phase-separated samples, a significant lattice thermal conductivity reduction of ∼50% might be expected. [ABSTRACT FROM AUTHOR]

We demonstrate the potential of metallurgical controlling of the phase separation reaction, by means of spark plasma sintering consolidation and subsequently controlled heat treatments sequence, for enhancement the thermoelectric properties of the p-type Ge0.87Pb0.13Te composition. Very high ZTs of up to ∼2, attributed to the nucleation of sub-micron phase separation domains and to comparable sized twinning and dislocation networks features, were observed. Based on the experimentally measured transport properties, combined with the previously reported phase separated n-type (Pb0.95Sn0.05Te)0.92(PbS)0.08 composition, a maximal efficiency value of ∼11.5% was theoretically calculated. These ZT and efficiency values are among the highest reported for single composition non-segmented bulk material legs. [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]

GeTe-based alloys have been considered as p -type thermoelectric materials for decades. Yet the fact that they possess intrinsically high concentration of cation germanium vacancies have triggered the thermoelectric community in finding alternatives and strategies to optimize their efficiency. While most of the published studies mainly discuss the stoichiometric alloy, here we demonstrate the introduction of excess germanium/tellurium to the system. The nonstoichiometric alloy is doped with bismuth, acting as a donor simultaneously with an increased number of vacancies, enabling higher solubility of other impurities (iodine/indium). This strategy and the mechanisms involved, has been investigated and correlated to the microstructural characteristics. ZT of ~1.6 was obtained but more importantly, it opens the opportunity for a potential route for further thermoelectric enhancement. • GeTe -based alloys shows ZT enhancement throughout all temperature range, reaching a 60% improvement compared to pure GeTe. • Achieved by electronic optimization using doping nonstoichiometric Ge x Te 1-x with both BiTe and cationic/anionic impurities. • General effective media evaluation enables the assessment of other routes for further transport properties enhancement. [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]