This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

The long-standing popularity of thermoelectric materials has contributed to the creation of various thermoelectric devices and stimulated the development of strategies to improve their thermoelectric performance. In this review, we aim to comprehensively summarize the state-of-the-art strategies for the realization of high-performance thermoelectric materials and devices by establishing the links between synthesis, structural characteristics, properties, underlying chemistry and physics, including structural design (point defects, dislocations, interfaces, inclusions, and pores), multidimensional design (quantum dots/wires, nanoparticles, nanowires, nano- or microbelts, few-layered nanosheets, nano- or microplates, thin films, single crystals, and polycrystalline bulks), and advanced device design (thermoelectric modules, miniature generators and coolers, and flexible thermoelectric generators). The outline of each strategy starts with a concise presentation of their fundamentals and carefully selected examples. In the end, we point out the controversies, challenges, and outlooks toward the future development of thermoelectric materials and devices. Overall, this review will serve to help materials scientists, chemists, and physicists, particularly students and young researchers, in selecting suitable strategies for the improvement of thermoelectrics and potentially other relevant energy conversion technologies.

Advanced Thermoelectric Design: From Materials and Structures to Devices

Thermoelectric materials: Energy conversion between heat and electricity

This review discusses recent developments and current research in high performance bulk thermoelectric materials, comprising nanostructuring, mesostructuring, band alignment, band engineering and synergistically defining key strategies for boosting the thermoelectric performance. To date, the dramatic enhancements in the figure of merit achieved in bulk thermoelectric materials have come either from the reduction in lattice thermal conductivity or improvement in power factors, or both of them. Here, we summarize these relationships between very large reduction of the lattice thermal conductivity with all-scale hierarchical architecturing, large enhanced Seebeck coefficients with intra-matrix electronic structure engineering, and control of the carrier mobility with matrix/inclusion band alignment, which enhance the power factor and reduce the lattice thermal conductivity. The new concept of hierarchical compositionally alloyed nanostructures to achieve these effects is presented. Systems based on PbTe, PbSe and PbS in which spectacular advances have been demonstrated are given particular emphasis. A discussion of future possible strategies is aimed at enhancing the thermoelectric figure of merit of these materials.

The panoscopic approach to high performance thermoelectrics

Thermoelectric effects enable direct conversion between thermal and electrical energy and provide an alternative route for power generation and refrigeration. Over the past ten years, the exploration of high-performance thermoelectric materials has attracted great attention from both an academic research perspective and with a view to industrial applications. This review summarizes the progress that has been made in recent years in developing thermoelectric materials with a high dimensionless figure of merits (ZT) and the related fabrication processes for producing nanostuctured materials. The challenge to develop thermoelectric materials with superior performance is to tailor the interconnected thermoelectric physical parameters — electrical conductivity, Seebeck coefficient and thermal conductivity — for a crystalline system. Nanostructures provide a chance to disconnect the linkage between thermal and electrical transport by introducing some new scattering mechanisms. Recent improvements in thermoelectric efficiency appear to be dominated by efforts to reduce the lattice thermal conductivity through nanostructural design. The materials focused in this review include Bi–Te alloys, skutterudite compounds, Ag–Pb–Sb–Te quaternary systems, half-Heusler compounds and some high-ZT oxides. Possible future strategies for developing thermoelectric materials are also discussed.

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High-performance nanostructured thermoelectric materials

Thermoelectric and mechanical properties of nano-SiC-dispersed Bi2Te3 fabricated by mechanical alloying and spark plasma sintering

Nano-SiC dispersed Bi2Te3 was synthesized by mechanical alloying (MA) followed by spark plasma sintering (SPS). The effects of SiC dispersion on the thermoelectric properties of the SPS-sintered Bi2Te3 alloys were investigated. The results revealed that SiC dispersion in the Bi2Te3 matrix increased the absolute value of Seebeck coefficient. Although the electrical resistance was increased somewhat, Bi2Te3 with 0.1 wt% SiC showed a higher power factor than Bi2Te3 without SiC. Because the dispersion of SiC nano-particles reduced the thermal conductivity at the same time, 0.1 wt% (∼0.24 vol% SiC) addition of SiC nano-particles increased the figure of merit of Bi2Te3 by 18%. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of nano-SiC dispersion on thermoelectric properties of Bi2Te3 polycrystals

Low temperature preparation and transport properties of ternary Pb-Bi-Te alloy

The invention discloses a pyroelectric material preparing method of nanometer SiC/Bi2Te3 radical in the energy resource and material technique domain, which comprises the following steps: using high-purity Bi powder and nanometer SiC as raw material; compounding Bi2Te3 chemical compound superfine powder by mechanical alloy; using discharge plasma sintering process to sinter Bi2Te3 predecessor fines of doping nanometer SiC granule for block The job step is composed of deploying raw material, mechanical alloying, discharge plasma sintering, example detecting The art work is easy; time of compounding chemical compound is short and temperature of sintering is low

Nanometer SiC/ Bi2Te3 base thermoelectric material preparation method

Polycrystalline samples of the ternary compound Pb 2 Bi 4 Te 5 were prepared by a solvothermal process based on the reaction between BiCl 3 , Pb(NO 3 ) 2 , Te, and KBH 4 in N , N -dimethylformamide (DMF), and followed by a post heat-treatment of compacted pellets. The microstructures of samples were characterized using XRD and SEM. The thermoelectric properties were determined by measuring the electric conductivity and the Seebeck coefficient. These samples show a disordered layered structure, with a maximum Seebeck coefficient of 84 μV/K around 520 K.

Jing Liu

Papers

Thermoelectric and mechanical properties of nano-SiC-dispersed Bi2Te3 fabricated by mechanical alloying and spark plasma sintering

Effect of nano-SiC dispersion on thermoelectric properties of Bi2Te3 polycrystals

Low temperature preparation and transport properties of ternary Pb-Bi-Te alloy

Nanometer SiC/ Bi2Te3 base thermoelectric material preparation method

Low Temperature Preparation and Transport Properties of Ternary Pb—Bi —Te Alloy.