Average Thermoelectric Figure Of Merit Research Articles

Enhanced Average Thermoelectric Figure of Merit of the PbTe-SrTe-MnTe Alloy.

Thermoelectric properties of Na-doped PbTe-SrTe system have been improved by the addition of Mn. The substitution of Mn for Pb modifies the band structure of the PbTe-SrTe alloy, which enlarges the band gap and increases the valence band degeneracy. This leads to increased thermopowers and power factors near room temperature, and the electronic contribution to the total thermal conductivity is also substantially reduced due to increased resistivity. Moreover, alloying of MnTe within the PbTe matrix introduces low angle grain boundaries, and significantly reduces the lattice thermal conductivity due to the dislocation scattering. A thermoelectric figure of merit as high as 1.98 and an enhancement of the average thermoelectric figure of merit by 18% are achieved for the sample with 4 at% Mn with respect to the Mn-free sample, which can be mainly attributed to the synergistic effects of the band structure modification and the dislocation scattering on phonon transport, both induced by alloying with MnTe. Our experimental results demonstrate the promising potential of PbTe-SrTe-MnTe system for the application of waste heat recovery.

Ultrahigh Thermoelectric Figure of Merit and Enhanced Mechanical Stability of p-type AgSb1–xZnxTe2

High-performance thermoelectric materials are desirable in the lower-medium temperature range (450–650 K) for low-grade waste heat recovery. We report a thermoelectric figure of merit (zT) of 1.9 at 585 K in p-type AgSb1–xZnxTe2, which is the highest value measured among the p-type materials in the 450–650 K range. A high average thermoelectric figure of merit (zTavg) of 1.3 is achieved in AgSb0.96Zn0.04Te2. Moreover, the AgSb1–xZnxTe2 sample exhibits a hardness value of ∼6.3 GPa (nanoindentation), which is significantly higher than that of the pristine AgSbTe2. Substitution of Zn in AgSbTe2 suppresses the formation of intrinsic Ag2Te impurity phases, which indeed increases the thermal and mechanical stability. The lattice thermal conductivity for AgSb1–xZnxTe2 samples is reasonably reduced compared to that of the pristine AgSbTe2 because of the significant solid solution point defect phonon scattering. Aliovalent Zn2+ doping in Sb3+ sites in AgSbTe2 increases the p-type carrier concentration, which boost...

Te-Doped Cu2Se nanoplates with a high average thermoelectric figure of merit

Te-doped Cu2Se nanostructures with a high averageZTvalue for Cu2Se0.98Te0.02.

Hot-Injection Synthesis of Cu-Doped Cu₂ZnSnSe₄ Nanocrystals to Reach Thermoelectric zT of 0.70 at 450°C.

As a new class of potential midrange temperature thermoelectric materials, quaternary chalcogenides like Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) suffer from low electrical conductivity due to insufficient doping. In this work, Cu-doped CZTSe nanocrystals consisting of polygon-like nanoparticles are synthesized with sufficient Cu doping contents. The hot-injection synthetic method, rather than the traditional one-pot method, in combination with the hot-pressing method is employed to produce the CZTSe nanocrystals. In Cu-doped CZTSe nanocrystals, the electrical conductivity is enhanced by substitution of Zn(2+) with Cu(+), which introduces additional holes as charge carriers. Meanwhile, the existence of boundaries between nanoparticles in as-synthesized CZTSe nanocrystals collectively results in intensive phonon-boundary scatterings, which remarkably reduce the lattice thermal conductivity. As a result, an average thermoelectric figure of merit of 0.70 is obtained at 450 °C, which is significantly larger than that of the state-of-the-art quaternary chalcogenides thermoelectric materials. The theoretical calculations from the Boltzmann transport equations and the modified effective medium approximation are in good agreement with the experimental data.

Effects of antimony content in MgAg0.97Sbx on output power and energy conversion efficiency

We report the effect of Sb content in MgAg0.97Sbx (x = 0.99, 0.9925, 0.995, and 1.00) on output power and leg efficiency. Due to the doubling of carrier concentration with increasing the Sb content, power factor is enhanced around 20% over the whole temperature range. Simultaneously, the average thermoelectric figure of merit (ZT) is even enhanced a little in spite of the increased corresponding thermal conductivity. We further calculated the engineering power factor (PF)eng, output power, engineering figure of merit (ZT)eng and leg efficiency by taking into account of the Thomson effect. Assuming Tc = 300 K and Th = 548 K, leg length ∼2 mm, an output power of ∼1.77 W cm−2 and leg efficiency η of ∼10.1% are finally obtained for the optimized composition MgAg0.97Sb0.995.

Enhanced average thermoelectric figure of merit of n-type PbTe1−xIx–MgTe

The average thermoelectric figure of meritZTof n-type PbTe1−xIx–MgTe is successfully enhanced through nano and meso structuring.

Microstructural effects on thermoelectric efficiency: A case study on magnesium silicide

Carrier transport and conversion efficiency of thermoelectric materials is not only governed by the intrinsic bulk material properties, but often heavily influenced by microstructural effects. Using Mg2Si—a very attractive, non-toxic and abundant material—as an example, the authors investigate the microstructural effects on thermoelectric transport in the material. Combining microstructural analysis (scanning electron microscopy, X-ray diffraction) with high-temperature transport measurements (Seebeck coefficient, electrical and thermal conductivity, charge carrier mobility), it is verified that small amounts of impurity phases can heavily impair electrical transport. Further electron microscopy studies confirm MgO functioning as a scattering center at the grain boundaries of the material. The effect of the impurity phases on the transport properties can be understood in a simple transport model based on a single parabolic band including grain boundary scattering. The model can be employed to assess material parameters such as the phonon deformation potential, the barrier height of the grain boundaries and the average size of the grains. Furthermore, the detrimental effect of MgO on thermoelectric efficiency is quantified. Compared with Sb-doped Mg2Si with optimized properties, a few per cent MgO decreases the average thermoelectric figure of merit by 30%.

Preparation of thermoelectric materials based on higher manganese silicide

Rhenium-doped higher manganese silicide based materials have been prepared by hot pressing. It has been shown that the pressing temperature of the materials can be lowered by adding titanium as a reductant or by sonication during pressing. The average thermoelectric figure of merit of the materials in the temperature range 600–900 K is Z ≅ 0.7 × 10−3 K−1.

Combination of large nanostructures and complex band structure for high performance thermoelectric lead telluride

The complexity of the valence band structure in p-type PbTe has been shown to enable a significant enhancement of the average thermoelectric figure of merit (zT) when heavily doped with Na. It has also been shown that when PbTe is nanostructured with large nanometer sized Ag2Te precipitates there is an enhancement of zT due to phonon scattering at the interfaces. The enhancement in zT resulting from these two mechanisms is of similar magnitude but, in principle, decoupled from one another. This work experimentally demonstrates a successful combination of the complexity in the valence band structure with the addition of nanostructuring to create a high performance thermoelectric material. These effects lead to a high zT over a wide temperature range with peak zT > 1.5 at T > 650 K in Na-doped PbTe/Ag2Te. This high average zT produces 30% higher efficiency (300–750 K) than pure Na-doped PbTe because of the nanostructures, while the complex valence band structure leads to twice the efficiency as the related n-type La-doped PbTe/Ag2Te without such band structure complexity.

InAs1-xPx as a Thermoelectric Material

Measurements of the electrical conductivity σ, the thermal conductivity K, and the Seebeck coefficient (thermoelectric power) α, of InAs1−xPx have been made at high temperatures with x varying from 0 to 0.4. Between 450° and 800°C, the average thermoelectric figure of merit (z = α2σ/K) increases moderately with x for small values of x, reaching a maximum near x = 0.1, and subsequently decreasing. Between 450 and 800°C, the average z for x = 0.1 is equal to 0.63 × 10−3(°K)−1, a 15% improvement over InAs. For the same figure of merit, the Seebeck coefficient and electric resistivity is higher in the ternary than in the binary InAs; this is advantageous for the design of thermoelectric devices. Previous values for the thermoelectric figure of merit of InAs are revised.