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Ta-doped Ti1-xTaxCoSb (0≤x≤0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900 K. The Ti1-xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1-xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900 K. This value is about ten times larger than that of the undoped TiCoSb compound. [ABSTRACT FROM AUTHOR]

The Cu–S compounds have been reported as promising thermoelectric materials with abundant element composition, low price, and low toxicity. In this work, Snx Cu1.8−x S samples with different Sn contents (x = 0.005, 0.01, 0.03, and 0.05) were fabricated by mechanical alloying combined with spark plasma sintering. The phase structure and microstructure of all the bulk samples were checked by X-ray diffraction (XRD) and field emission scanning electron microscopy respectively. The thermoelectric transport properties, such as electrical conductivity, Seebeck coefficient, carrier concentration, carrier mobility, and thermal conductivity, were measured. The effect of second phase introduced by Sn addition on the thermoelectric properties of Cu–S system was investigated. The thermoelectric properties of samples were improved by the precipitations of two different second phases (Cu2SnS3 and Cu4SnS4). The second phase species depend on the Sn contents. Finally, the Sn0.01Cu1.79S bulk sample obtained the highest ZT value of 0.81 at 773 K, which is 1.6-fold higher than that of the pristine Cu1.8S sample due to the significantly reduced thermal conductivity by second phase and nanopores scattering. [ABSTRACT FROM AUTHOR]

PbTe1− xSe x-2%Na-y%SrTe system is investigated and a high maximum ZT of 2.3 at 923 K for PbTe0.85Se0.15-2%Na-4%SrTe is reported. This is achieved by performing electronic band structures modifications as well as all-scale hierarchical structuring and combining the two effects. It is found that high ZTs in PbTe0.85Se0.15-2%Na-4%SrTe are possible at all temperature from 300 to 873 K with an average ZTave of 1.23. The high performance in PbTe1− xSe x-2%Na-y%SrTe can be achieved by either choosing PbTe-2Na-4SrTe or PbTe0.85Se0.15-2Na as a matrix. At room temperature the carrier mobility shows negligible variations as SrTe fraction is increased, however the lattice thermal conductivity is significantly reduced from ≈1.1 to ≈0.82 W m−1 K−1 when 5.0% SrTe is added, correspondingly, the lattice thermal conductivity at 923 K decreases from ≈0.59 to ≈0.43 W m−1 K−1. The power factor maxima of PbTe1− xSe x-2Na-4SrTe shift systematically to higher temperature with rising Se fractions due to bands divergence. The maximum power factors reach ≈27, ≈30, ≈31 μW cm−1 K−2 for the x = 0, 0.05, and 0.15 samples peak at 473, 573, and 623 K, respectively. The results indicate that ZT can be increased by synergistic integration of band structure engineering and all-scale hierarchical architectures. [ABSTRACT FROM AUTHOR]

Lead-free p-type AgSn 4 SbTe 6 based thermoelectric nanocomposites were fabricated by a process combining mechanical alloys (MA) and spark plasma sintering (SPS). It is found that dispersing SiC nanoparticles into the AgSn 4 SbTe 6 matrix can enhance the thermoelectric properties significantly. SiC nanoinclusions can increase the power factor mainly due to improved electrical conductivity while slightly increasing the Seebeck coefficient, in addition to reducing the thermal conductivity through enhancing phonon scattering. A high dimensionless figure of merit (ZT) value up to 1.0 at a relatively low temperature (723 K) is achieved in AgSn 4 SbTe 6 incorporated with a small amount (1 vol%) of SiC nanoparticles. This work validated the effectiveness of SiC nanodispersion in enhancing thermoelectric performance of AgSn 4 SbTe 6 , by which a simple process yields a high ZT equivalent to the record one reported for this materials fabricated by a melting process. [ABSTRACT FROM AUTHOR]

Abstract: Fine-grained Ti-doped FeVSb half-Heusler alloys were synthesized by combining mechanical alloying and spark plasma sintering and their thermoelectric properties were investigated with an emphasis on the influences of Ti doping and phase purity. It was found that substituting V with Ti can change the electrical transport behavior from n-type to p-type due to one less valence electron of Ti than V, and the sample with nominal composition FeV0.8Ti0.4Sb exhibits the largest Seebeck coefficient and the maximum power factor. By optimizing the sintering temperature and applying annealing treatment, the power factor is significantly improved and the thermal conductivity is reduced simultaneously, resulting in a ZT value of 0.43 at 500°C, which is relatively high as for p-type half-Heusler alloys containing earth-abundant elements. [Copyright &y& Elsevier]

A composite structure with two separately doped phases was introduced into Ni-doped LaCoO3 ceramics to enhance its electrical conductivity while keeping low thermal conductivity. LaCo0.9 Ni0.1 O3−δ nanoparticles were dispersed in the sol solution of La0.9 Sr0.1 Co0.9 Ni0.1 O3−δ and separated from the solution by centrifugation, which were then calcined and consolidated using normal sintering in air. The electrical conductivity of the coated samples was obviously increased, although the Seebeck coefficient was slightly decreased by the above particle- coating method, resulting in a great improvement of power factor. The Seebeck coefficient and electrical conductivity are strongly dependent on the concentration of La0.9 Sr0.1 Co0.9 Ni0.1 O3−δ sol, which affects the coating content, but the thermal conductivity is less affected by its concentration especially at room temperature. The power factor was increased to 2.58 × 10−4 Wm−1 K−2 at room temperature, resulting in a twofold enhancement in a peak ZT value at 373 K for the coated sample as compared with that without coating. [ABSTRACT FROM AUTHOR]

Single-phase polycrystalline LaSrTiO ( x = 0, 0.04, 0.06, 0.08, and 0.12) ceramics were prepared by the conventional solid-state reaction method using high-activity hydroxides as the raw materials. The electrical conductivity of all the samples increased with increasing x value and decreased with measurement temperature, while the thermal conductivity decreased with increasing x value and measurement temperature. The LaSrTiO sample showed the lowest thermal conductivity of 2.45 W m K at 873 K and the largest ZT of 0.28 at 773 K. The present work revealed that hydroxides with high activity as raw materials are beneficial to improve the thermoelectric properties, especially to decrease the thermal conductivity. [ABSTRACT FROM AUTHOR]

BiSbTe bulk alloys are known as the best p-type thermoelectric materials near room temperature. In this work, single-phase BiSbTe ( x = 0.2, 0.25, 0.3, 0.34, 0.38, 0.42, 0.46, and 0.5) alloys were prepared by spark plasma sintering (SPS) using mechanical alloying (MA)-derived powders. A small amount (0.1 vol.%) of SiC nanoparticles was added to improve the mechanical properties and to reduce the thermal conductivity of the alloys. The electrical resistivity decreases significantly with increasing ratio of Sb to Bi in spite of the weaker decreasing trend in Seebeck coefficient, whereby the power factor at 323 K reaches 3.14 × 10 W/mK for a sample with x = 0.3, obviously higher than that at x = 0.5 (2.27 × 10 W/mK), a composition commonly used for ingots. Higher thermal conductivities at low temperatures are obtained at the compositions with lower x values, but they tend to decrease with temperature. As a result, higher ZT values are obtained for BiSbTe, with a maximum ZT value of 1.23 at 423 K, about twice the ZT value (about 0.6) of BiSbTe at the same temperature. [ABSTRACT FROM AUTHOR]

Polycrystalline p-type BiSbTe and n-type BiTeSe thermoelectric (TE) alloys containing a small amount (vol.% ≤5) of SiC nanoparticles were fabricated by mechanical alloying and spark plasma sintering. It was revealed that the effects of SiC addition on TE properties can be different between p-type and n-type BiTe-based alloys. SiC addition slightly increased the power factor of the p-type materials by decreasing both the electrical resistivity ( ρ) and Seebeck coefficient ( α), but decreased the power factor of n-type materials by increasing both ρ and α. Regardless of the conductivity type, the thermal conductivity was reduced by dispersing SiC nanoparticles in the BiTe-based alloy matrix. As a result, a small amount (0.1 vol.%) of SiC addition increased the maximum dimensionless figure of merit ( ZT) of the p-type BiSbTe alloys from 0.88 for the SiC-free sample to 0.97 at 323 K, though no improvement in TE performance was obtained in the case of n-type BiTeSe alloys. Importantly, the SiC-dispersed alloys showed better mechanical properties, which can improve material machinability and device reliability. [ABSTRACT FROM AUTHOR]

Bismuth sulfide (BiS) polycrystalline samples were fabricated by mechanical alloying (MA) combined with spark plasma sintering (SPS). The microstructure and electrical transport properties were investigated with special emphasis on the influence of the ball-milling process. BiS compound powders could be readily synthesized directly from elemental powders under all the investigated conditions, and highly dense n-type bulk BiS samples with high density (>95%) were fabricated by the subsequent SPS process. Changing the MA conditions had no apparent influence on the microstructure or phase structure of the MA-derived BiS powders, but the electrical properties and thermopower of the SPS-sintered BiS bulk samples were greatly dependent on the MA speed and time. The power factor of BiS was increased to 233 μW K m at 573 K by optimizing the ball-milling process. This power factor is higher than values reported to date for Bi-S binary samples without texture. [ABSTRACT FROM AUTHOR]

Silver antimonate (AgSbO) is a potential high-temperature thermoelectric oxide with a low thermal conductivity, but it is difficult to fabricate dense bulk material with high phase purity. Well-dispersed AgSbO nanopowder with an average diameter of 50 nm was synthesized by an ion-exchange process in this study, the sintering density of which was apparently enhanced. Nearly single-phase AgSbO ceramic samples with a relative density close to 90% were obtained when sintered at a relatively low temperature (1273 K). The electrical conductivity of AgSbO increased greatly with increasing sintering temperature, probably because of defects originating from the compositional deviation caused by sintering, in addition to increased density. This study also confirmed that AgSbO had a low thermal conductivity, from 1.1 W m K at room temperature to 0.8 W m K at 673 K. [ABSTRACT FROM AUTHOR]

High-performance nanostructured AgPbSbTe thermoelectric materials have been fabricated using mechanical alloying and spark plasma sintering. A decrease in Ag content causes a great reduction in thermal conductivity and a prominent increase in ZT value. A minimum thermal conductivity of 0.86 W/m K and a high ZT value of 1.5 (700 K) have been obtained for the AgPbSbTe sample. The smaller and denser nanoscopic regions with reduced Ag content are thought to enhance phonon scattering, resulting in decreased thermal conductivity and enhanced thermoelectric performance. [ABSTRACT FROM AUTHOR]

microfabrication process has been developed to elaborate microscale thermoelectric modules with high-aspect-ratio pillars assembled in a glass micromold, whose multi-channels are formed by combining mechanical machining and hot-pressing processes. This paper describes how to fill the multi-channel glass molds with thermoelectric materials by introducing a patterned electrochemical deposition method, in which a deposition cathode with two series of interdigital electrodes is designed. A reverse-pulsed electrodeposition method is found effective to overcome the difficulty for deep-filling that is required for fabricating thermoelectric pillars with high aspect ratios. A pulse circle of −200 mV for 4 s, +500 mV for 1 s, and 0 mV for 3 s (vs. saturated calomel electrode) was determined for preparing N-type BiTe arrays with a high aspect ratio exceeding ten from a solution containing 0.0075 M Bi and 0.01 M HTeO. The as-deposited pillars show reasonable electrical resistivity as compared with common bulk BiTe materials. [ABSTRACT FROM AUTHOR]

Abstract: Nearly single-phased TiNiSn half-Heusler compound thermoelectric materials were synthesized by combining mechanical alloying (MA) and spark plasma sintering (SPS) in order to reduce its thermal conductivity by refining the grain sizes. Although TiNiSn compound powders were not synthesized directly via MA, dense bulk samples of TiNiSn compound were obtained by the subsequent SPS treatment. It was found that an excessive Ti addition relative to the TiNiSn stoichiometry is effective in increasing the phase purity of TiNiSn half-Heusler phase in the bulk samples, by compensating for the Ti loss caused by the oxidation of Ti powders and MA processing. The maximum power factor value obtained in the Ti-compensated sample is 1720μWm−1 K−2 at 685K. A relatively high ZT value of 0.32 is achieved at 785K for the present undoped TiNiSn compound polycrystals. [Copyright &y& Elsevier]

La2− xR xCuO4 (R: Pr, Y, Nb) polycrystalline ceramics have been prepared by a spark plasma sintering process. Analysis of the microstructure and phase composition shows that pure La2CuO4 ceramics with a high density can be obtained, and no impurity phases appear. All the samples exhibit a metal–semiconductor transition behavior at ∼750 K, which could be ascribed to the decreasing charge density as a result of loss of oxygen atoms and various conduction mechanisms in these La2CuO4-based ceramics. Our results indicate that the La1.98Y0.02CuO4 ceramics show large thermoelectric power ∼1.0 × 10−3μW·(m·K2)−1, and the evaluated ZT can reach 0.17 at 330 K, which potentially make them useful for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Nanostructured Ag0.8Pbm+xSbTem+2 (m = 18, x = 4.5) system thermoelectric materials have been fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) methods followed by annealing for several days to investigate the effect on microstructure and thermoelectric performance. It was found that appropriate annealing treatment could reduce both the electrical resistivity and the thermal conductivity at the same time, consequently greatly enhancing the thermoelectric performance. A low electrical resistivity of 2 × 10-3 Ohm-cm and low thermal conductivity of 0.89 W m-1 K-1 were obtained for the sample annealed for 30 days at 700 K. The very low thermal conductivity is supposed to be due to the nanoscopic Ag/Sb-rich regions embedded in the matrix. A high ZT value of 1.5 at 700 K has been achieved for the sample annealed for 30 days. [ABSTRACT FROM AUTHOR]

Highly dense La2CuO4 ceramics have been prepared by the spark plasma sintering technique. Temperature dependence of electrical conductivity indicates that La2CuO4 ceramics sintered at over 875°C exhibit a metal-like behavior, which should be ascribed to the special La2CuO4 crystal structure and its correlation splitting of the half-filled d x2− y2 band. Our experimental data indicate that all of the La2CuO4 samples exhibit positive thermoelectric power in the whole measuring temperature range, indicating that the majority of charge carriers are holes. It is desirable to obtain good thermoelectric performance for this system by optimizing the electrical properties and reducing the thermal conductivity. [ABSTRACT FROM AUTHOR]

Thermoelectric microgenerators and microcoolers are becoming technologically important for microelectromechanical systems (MEMS), but the conventional cutting and assembling techniques have limitation in miniaturizing the dimensions of thermoelectric devices to the micrometer order. We have combined MEMS technology and materials processing into a novel process to manufacture thermoelectric micro-modules with densely aligned fine-scale and high-aspect-ratio P–N elements. Our process consists of the following major steps: (1) micromachining a silicon mold; (2) filling the mold with thermoelectric materials; (3) connecting P- and N-type elements and assembling the whole module. By using the present process, Bi–Sb–Te system thermoelectric elements of 300 μm height and 40 μm cross-sectional width can be fabricated successfully. [Copyright &y& Elsevier]

Highly (00l) oriented Ca3Co4O9-based ceramics were fabricated by spark plasma sintering combined with a dynamic forging process. The grain orientation is effective in lowering the electrical resistivity and enhancing the thermoelectric power factor but with little influence on the Seebeck coefficient. A metallic-to-semiconducting transition temperature can be observed and the activation energy is almost independent of the La-doping. All of the Ca3Co4O9-based ceramic samples exhibit large thermoelectric power, and the figure of merit for La-doped Ca3Co4O9 sample can reach 0.26 at 975 K, which can be a promising candidate of p-type material for high-temperature thermoelectric application. [ABSTRACT FROM AUTHOR]

Polycrystalline AgSbTe2 ternary compound materials with high phase purity were fabricated using a combined process of mechanical alloying and spark plasma sintering. It was found that stoichiometric AgSbTe2 is a promising composition for low-and-mediate temperature applications, whose ZT reaches 1.59 at 673 K, benefiting from its extremely low thermal conductivity (0.30 W/mK) in addition to its low electrical resistivity (<1.1×10-4 Ω m) and large positive Seebeck coefficient (260 μV/K). On the other hand, deviating from this formula would lead to unstable phase structures and higher thermal conductivity, which make the samples less attractive as thermoelectric materials or components of thermoelectric systems. [ABSTRACT FROM AUTHOR]

The effect of additional carrier pocket (ACP) on the thermoelectric property is investigated based on the multiband model, indicating that an ACP indeed enhances the power factor, and hence the thermoelectric figure of merit. The established model can be used to well explain the experimental observations in skutterudite compounds that a small addition of Ni or Pd significantly enhances power factor. However, the ACP effect works only when the edge energy difference EΔ between major carrier pocket and ACP is less than 5kBT. [ABSTRACT FROM AUTHOR]

Abstract: Both vacuum melting and mechanical alloying (MA) were applied to the fabrication of AgPb x SbTe20 (x =20, 21 and 22.5) as a promising thermoelectric material to investigate the processing influence on its thermoelectric properties. The AgPb x SbTe20 compound powders were prepared by pulverizing the melted ingots or directly from MA, which were then consolidated to fine-grained bulk materials by spark plasma sintering (SPS). A high ZT value of 1.25 at 725K was observed in the AgPb20SbTe20 samples fabricated by both methods. Thermoelectric properties of all AgPb x SbTe20 compounds synthesized by vacuum melting method are nearly the same as that of those fabricated by MA combined with SPS in the whole measured temperature range. Considering the complexity of the melting method but with the same results as the MA–SPS method, the present work revealed that the MA–SPS process is more suitable for the fabrication of PbTe-based thermoelectric materials. [Copyright &y& Elsevier]

Abstract: Single-phase polycrystalline La0.08Sr0.92TiO3 ceramics were prepared by spark plasma sintering (SPS) using sol–gel-derived powders. The La0.08Sr0.92TiO3 bulks had highly relative density (∼92%), and the grain size of the samples obviously grew from 300 nm to 3 μm when the SPS temperature increased from 1203 to 1473 K. The electrical conductivity increased with SPS-processing temperature owing to the increase of relative density, grain size, and oxygen vacancies due to the reducing atmosphere of SPS. The absolute value of Seebeck coefficient increased as the SPS temperature increased from 1203 to 1373 K, and then decreased by further increasing SPS temperature to 1473 K. The sample SPSed at 1373 K had the largest absolute value of Seebeck coefficient of 196 μVK−1 at 679 K. Sol–gel process and SPS can significantly decrease the thermal conductivity of SrTiO3 based ceramics, whose lowest value was reduced to 1.19 Wm−1k−1 at 773 K in the sample SPSed at 1203 K. The maximum ZT value of 0.08 was obtained at 679 K for the sample SPSed at 1473 K. [Copyright &y& Elsevier]

Abstract: Highly dense n-type Bi2Te3 dispersed with x vol% nano-SiC particles (x =0, 0.1, 0.5, 1.0) thermoelectric materials were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The effects of nano-SiC addition on the thermoelectric and mechanical properties were studied. Compared with Bi2Te3 matrix, Bi2Te3 materials dispersed with nano-SiC show increased Seebeck coefficient, decreased electrical conductivity, and reduced thermal conductivity as well in the measured temperature range of 323–523K. The maximum dimensionless figure of merit (ZT max) was improved from 0.99 for Bi2Te3 sample to 1.04 for 0.1vol% SiC dispersed Bi2Te3 sample at 423K. The Vickers hardness increased linearly from 0.62 to 0.79GPa as 1.0vol% SiC was added. The highest fracture toughness of 1.34MPam1/2 was obtained for 0.1vol% SiC addition, and the highest Young''s modulus of 42.7GPa was obtained for 0.5vol% SiC added sample. [Copyright &y& Elsevier]

Thermoelectric materials transfer heat and electrical energy, hence they are useful for power generation or cooling applications. Many of these materials have narrow bandgaps, especially for cooling applications. We developed SnSe crystals with a wide bandgap (Eg ≈ 33 kBT) with attractive thermoelectric properties through Pb alloying. The momentum and energy multiband alignments promoted by Pb alloying resulted in an ultrahigh power factor of ~75 mW cm–1 K–2 at 300 K, and an average figure of merit ZT of ~1.90. We found that a 31-pair thermoelectric device can produce a power generation efficiency of ~4.4% and a cooling DTmax of ~45.7 K. These results demonstrate that wide-bandgap compounds can be used for thermoelectric cooling applications. [ABSTRACT FROM AUTHOR]

Thermoelectric materials can directly convert heat to electricity and vice versa. ZT (= S 2 σ T / κ) is usually used for evaluating the performance of thermoelectric materials. Improving ZT is a challenging task because of the strong interdependence among the Seebeck coefficient (S), electrical conductivity (σ) and thermal conductivity (κ). This review provides a summary of some promising thermoelectric materials in different developing stages with emphasis on the corresponding strategies for thermoelectric performance enhancement. In addition, the number of recent publications on some representative thermoelectric materials is summarized, addressing the current research interests in this field. Thermoelectricity still need intensified scientific efforts to meet the practical demand. • Summarize most promising bulk thermoelectric materials. • Enumerate traditional thermoelectric materials and the corresponding performance enhancing strategies and developing status. • Some emerging and burgeoning materials with outstanding thermoelectric performance are reviewed. [ABSTRACT FROM AUTHOR]

Ternary copper tin sulfide (Cu–Sn–S) compounds have been investigated for decades as promising candidates of earth-abundant thin film solar cell absorbers. Cu 2 SnS 3 is a representative member of this material system, and is highly expected to be a potential thermoelectric material by the first-principles calculations. In this work, Cu 2 SnS 3 bulk materials were synthesized by the mechanical alloying (MA) combined with spark plasma sintering (SPS), and their crystal structures, electronic transport properties and enhanced thermoelectric performance were systematically investigated. We found that pristine Cu 2 SnS 3 is a p-type thermoelectric material with a relatively high thermopower up to 300 μV/K and low thermal conductivity below 1.0 W/m K above 700 K. It revealed that In doping is an effective means to improve the electrical transport properties, which leads to a figure of merit ( ZT ) of Cu 2 Sn 0.9 In 0.1 S 3 close to 0.6 at the relatively low temperature (773 K). [ABSTRACT FROM AUTHOR]

BiCuSeO-based oxyselenide compounds show promising thermoelectric properties, but its thermal stability and oxidation behavior are unknown, which were investigated in the present work with a PbTe-based thermoelectric alloy as a comparison. It was revealed that the BiCuSeO polycrystalline materials displayed much better thermal stability in air than the PbTe-based alloys that were severely oxidized at 573 K, resulting in a decreased density and significantly reduced electrical conductivity. Nevertheless, it was found that the BiCuSeO-based thermoelectric materials could not be used in air for a long time as a conventional oxide at high temperatures; apparent decomposition occurred in the BiCuSeO samples when heated at 773 K, although at 573 K the oxidation was limited to the surface accompanied by the formation of bismuth oxide. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanocrystalline n-type Bi2Te3 films are deposited by magnetron sputtering. [•] Pb doping increases the Seebeck coefficient of Bi2Te3 thin films. [•] Pb doping reduces the carrier thermal conductivity of Bi2Te3 thin films. [•] Optimal Pb doping enhances the power factor of Bi2Te3 thin films. [ABSTRACT FROM AUTHOR]

Abstract: Bismuth sulfide powders were synthesized by mechanical alloying (MA) and then consolidated by spark plasma sintering (SPS) technique. In order to improve the electrical transport properties of bismuth sulfides, the carrier concentration was optimized by modifying chemical composition of sulfur through producing sulfur vacancies, and the carrier mobility was enhanced by a two-step SPS as a hot-forging process through increasing grain orientation. The electrical resistivity of bismuth sulfides was reduced to 10−4 from 10−2 Ωm by optimizing sulfur content, and further lowered by hot-forging, whereby the power factor was significantly increased from 91 to 254μW/mK2. The hot-forged Bi2S2.90 sample showed the highest ZT=0.11 (at 523K), which is higher than the reported value. The present work revealed that bismuth sulfide compounds as a promising candidate of thermoelectric materials can be synthesized by a simple process. [Copyright &y& Elsevier]

AgSnmSbTem+2 (m = 2, 4, 10, 18) thermoelectric materials are prepared by mechanical alloying of the elements in a planetary ball mill followed by spark plasma sintering (50 MPa, 749 K, 5 min). [ABSTRACT FROM AUTHOR]