Over the past decades, thermoelectric materials have advanced significantly, yet materials such as Sb2Si2Te6, which are challenging to synthesize chemically, often require lengthy and complex preparation processes, hindering their development. In this work, we prepare polycrystalline Sb2Si2Te6 bulk from elemental precursors using a high-pressure synthesis (HPS) method. This method offers significant advantages in efficiency and preparation duration. The applied pressure promotes an isotropic microstructure and regulates the thermoelectric properties by controlling precipitate contents, grain size, and twinning. Although an increase in thermal conductivity, mostly due to the notable increase in electrical conductivity, leads to less favorable thermal conductivity near room temperature compared to samples prepared using conventional methods, a beneficial reversal occurs at high temperatures. The polycrystalline Sb2Si2Te6 sample synthesized at 2 GPa demonstrates a peak ZT value of 1.1 at 773 K, outperforming most pristine Sb2Si2Te6 materials. This work demonstrates an efficient strategy for optimizing Sb2Si2Te6 performance and offers a new synthesis pathway for other challenging thermoelectric materials.

With the advantages of eco-friendliness, low cost, and low density, Mg2(Si,Sn) solid solutions are promising candidates for thermoelectric applications. In this work, Sb-doped Mg2Si0.4Sn0.6 bulks were prepared with a combined method of solid-state reaction and high pressure synthesis, followed by spark plasma sintering. Our investigations show that Sb doping optimizes the carrier concentration, while Si/Sn alloying effectively suppresses the lattice thermal conductivity and induces a convergence of the two lowest-lying conduction bands. Additionally, numerous coherent Sn-rich nanoprecipitates are formed within micron-sized grains. All these factors contribute synergistically to improving the thermoelectric properties of Mg2Si0.4Sn0.6. The optimal Mg2(Si0.4Sn0.6)0.985Sb0.015 exhibits a power factor higher than 4000 μW·m−1·K−2 and a lattice thermal conductivity less than 0.8 W·m−1·K−1 at temperatures higher than 600 K, leading to the highest ZT of 1.61 at 823 K. Current work demonstrates an effective approach to enhancing the thermoelectric performance of n-type Mg2X solid solutions through doping, alloying, and microstructure modification.

Porous structures have attracted considerable interest for their impact on the transport and mechanical characteristics of materials. The fabrication of porous materials, however, often involves intricate preprocessing steps and typically lacks the ability to tailor porosity with ease. In the present study, we present a straightforward method to prepare porous Bi2Te2.5Se0.5 samples by employing low-pressure spark plasma sintering, with the porosity regulated by preset mass density using a modified graphite mold. This approach resulted in a substantial decrease in thermal conductivity, attributed to the introduction of pores that reduce mass density and disrupt phonon transmission. An accompanying decrease in electrical conductivity was also noted, arising from reduced carrier concentration and mobility. Despite these variations, all porous samples maintained similar levels of thermoelectric performance, with a peak zT of ca. 0.9 at 373 K. The average zT within the temperature range of 298–500 K remained slightly above 0.8 for all samples. Furthermore, the porous samples exhibited greatly enhanced mechanical properties. This work demonstrates a versatile and adaptable method to produce porous materials with controllable porosity, potentially applicable to other porous thermoelectric systems.

A series of n-type Mg2(Si0.3Sn0.7)1-xBix compounds with 0 <= x <= 0.02 were successfully synthesized through a combined approach involving solid-state reaction, high-pressure synthesis, and spark plasma sintering techniques. The method yielded homogeneously distributed single-phase materials at the micron scale, although minor compositional variations were detected within nanoscale precipitates embedded in the grains. The sample with Bi content of 0.01 exhibited enhanced thermoelectric properties, reaching a peak thermoelectric figure of merit (ZT) of 1.45 at 700 K while maintaining an average ZT of about 1.1 over the temperature range of 300_ 773 K. The enhancement in thermoelectric performance is ascribed to the optimized carrier concentration, band convergence, and refined microstructure. The findings suggest a simplified approach to doping that could be beneficial in creating high-performance thermoelectric materials for energy conversion.

Porous structures have attracted considerable interest for their impact on the transport and mechanical characteristics of materials. The fabrication of porous materials, however, often involves intricate preprocessing steps and typically lacks the ability to tailor porosity with ease. In the present study, we present a straightforward method to prepare porous Bi2Te2·5Se0.5 samples by employing low-pressure spark plasma sintering, with the porosity regulated by preset mass density using a modified graphite mold. This approach resulted in a substantial decrease in thermal conductivity, attributed to the introduction of pores that reduce mass density and disrupt phonon transmission. An accompanying decrease in electrical conductivity was also noted, arising from reduced carrier concentration and mobility. Despite these variations, all porous samples maintained similar levels of thermoelectric performance, with a peak zT of ca. 0.9 at 373 K. The average zT within the temperature range of 298–500 K remained slightly above 0.8 for all samples. Furthermore, the porous samples exhibited greatly enhanced mechanical properties. This work demonstrates a versatile and adaptable method to produce porous materials with controllable porosity, potentially applicable to other porous thermoelectric systems.

Porous structures have attracted considerable interest for their impact on the transport and mechanical characteristics of materials. The fabrication of porous materials, however, often involves intricate preprocessing steps and typically lacks the ability to tailor porosity with ease. In the present study, we present a straightforward method to prepare porous Bi 2 Te 2.5 Se 0.5 samples by employing low-pressure spark plasma sintering, with the porosity regulated by preset mass density using a modified graphite mold. This approach resulted in a substantial decrease in thermal conductivity, attributed to the introduction of pores that reduce mass density and disrupt phonon transmission. An accompanying decrease in electrical conductivity was also noted, arising from reduced carrier concentration and mobility. Despite these variations, all porous samples maintained similar levels of thermoelectric performance, with a peak zT of ca . 0.9 at 373 K. The average zT within the temperature range of 298-500 K remained slightly above 0.8 for all samples. Furthermore, the porous samples exhibited greatly enhanced mechanical properties. This work demonstrates a versatile and adaptable method to produce porous materials with controllable porosity, potentially applicable to other porous thermoelectric systems.

The optimal carrier concentration of thermoelectric materials increases with increasing temperature. However, conventional aliovalent doping usually provides an approximately constant carrier concentration over the whole temperature range, which can only match the optimal carrier concentration in a narrow temperature range. In this work, n-type indium and aluminum codoped PbTe were prepared with high-pressure synthesis, followed by spark plasma sintering. While Al doping can provide a roughly constant carrier concentration with varying temperatures, In doping can trap electrons at low temperatures and release them at high temperatures, thus optimizing the carrier concentration over a broad temperature range. As a result, both electrical transport properties and thermal conductivity are optimized, and a significantly enhanced thermoelectric performance is achieved in InxAl0.02Pb0.98Te. The optimal In0.008Al0.02Pb0.98Te shows a peak ZT of 1.3 and an average ZT of 1, with a decent conversion efficiency of 14%. Current work demonstrates that optimizing carrier concentration with varying temperatures is effective to enhance the thermoelectric performance of n-type PbTe.

The outstanding thermoelectric material, SnSe, is also known for its inferior mechanical properties, which bring great inconvenience for its application in thermoelectric devices. In this work, SnSe bulks were prepared via a sequential procedure of high-pressure synthesis (HPS), ball milling, and spark plasma sintering (SPS). The produced polycrystalline samples with a unique microstructure of tightly-bound quasi-equiaxed grains exhibited excellent mechanical properties. The Vickers hardness (HV), compressive strength (sigma(c)), and bending strength (sigma(b)) reached 1.1 GPa, 300 MPa, and 90 MPa, respectively, all of which are far superior to those of ordinary polycrystalline SnSe. Furthermore, the microstructures did not deteriorate thermoelectric performance. This work demonstrated an effective procedure to prepare polycrystalline microstructure-engineered SnSe materials, which not only show advantages in device applications but also shed light on property enhancement for other layer-structured thermoelectric materials.

Porous BiSbTe bulks with a unique microstructure featuring closely bonded quasi-equiaxed grains show excellent thermoelectric and mechanical properties.

P-type CaxFe1.3CO2.7Sb12 skutterudites were successfully synthesized with a high pressure synthesis method followed by spark plasma sintering. The structure, composition and thermoelectric properties were investigated. With fixed Fe substitution level, the hole concentration was tuned with Ca filling. Compared with the unfilled Co(3.2)5Fe(0.73)Sb(12), Ca-filled samples possessed a relatively large effective mass, which is beneficial for enhancements in Seebeck coefficient and power factor. Moreover, the joint impurity and rattling mode scattering further suppressed the lattice thermal conductivity. Consequently, the Ca0.6Fe1.3CO2.7Sb12 sample showed the optimal ZT of 0.70 at 820 K. Composition analysis and simple electron counting suggested 0.77 hole per molecular formula for this sample, close to the value (about 0.7) we proposed for optimal filling and substitution contents in Co-rich p-type skutterudites. (C) 2020 Elsevier B.V. All rights reserved.

Single elemental doped n-type PbTe compounds were successfully prepared with high pressure synthesis followed by spark plasma sintering. Thermoelectric properties investigation indicates the performance of these samples is regulated by the carrier concentration. For each doping element, the maximal ZT increases and occurs at higher temperature with increasing carrier concentration. However, the average ZT over the measurement temperature range is getting smaller due to substantially smaller ZT at low temperature. For the optimal carrier concentration near 1 x 10(19) cm(-3), a relatively high average ZT of ca. 0.7 is achieved for most of the doping elements. Since the average ZT determines the device performance of thermoelectric materials, our study can serve as a basis for further performance enhancement of n-type PbTe through combining strategies of dynamic doping and/or hierarchical phonon scattering. (C) 2019 Elsevier B.V. All rights reserved.