Recently a significant figure-of-merit (ZT) improvement in the most-studied existing thermoelectric materials has been achieved by creating nanograins and nanostructures in the grains using the combination of high-energy ball milling and a direct-current-induced hot-press process. Thermoelectric transport measurements, coupled with microstructure studies and theoretical modeling, show that the ZT improvement is the result of low lattice thermal conductivity due to the increased phonon scattering by grain boundaries and structural defects. In this article, the synthesis process and the relationship between the microstructures and the thermoelectric properties of the nanostructured thermoelectric bulk materials with an enhanced ZT value are reviewed. It is expected that the nanostructured materials described here will be useful for a variety of applications such as waste heat recovery, solar energy conversion, and environmentally friendly refrigeration.

Enhancement of Thermoelectric Figure-of-Merit by a Bulk Nanostructuring Approach

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), en...

Compound Copper Chalcogenide Nanocrystals

We report a procedure to prepare highly monodisperse copper telluride nanocubes, nanoplates, and nanorods. The procedure is based on the reaction of a copper salt with trioctylphosphine telluride in the presence of lithium bis(trimethylsilyl)amide and oleylamine. CuTe nanocrystals display a strong near-infrared optical absorption associated with localized surface plasmon resonances. We exploit this plasmon resonance for the design of surface-enhanced Raman scattering sensors for unconventional optical probes. Furthermore, we also report here our preliminary analysis of the use of CuTe nanocrystals as cytotoxic and photothermal agents.

CuTe Nanocrystals: Shape and Size Control, Plasmonic Properties, and Use as SERS Probes and Photothermal Agents

An electrodeposition method for fabrication of CuTe and Cu2Te thin films is presented. The films' growth is based on the epitaxial electrodeposition of Cu and Te alternately with different electrochemical parameter, respectively. The deposited thin films were characterized by X-ray diffraction (XRD), field emission scanning electronic microscopy (FE-SEM) with an energy dispersive X-ray (EDX) analyzer, and FTIR studies. The results suggest that the epitaxial electrodeposition is an ideal method for deposition of compound semiconductor films for photoelectric applications.

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Electrodeposition and characterization of CuTe and Cu 2 Te thin films

Nanocrystalline copper chalcogenides, CuSe and Cu2Te, have been synthesized by reactions between elemental Cu and Se or Te under microwave irradiation for several minutes. The products have been characterized by XRD, TEM, and XPS.

Microwave-assisted elemental direct reaction route to nanocrystalline copper chalcogenides CuSe and Cu2Te

Synthesis by mechanical alloying and thermoelectric properties of Cu2Te

Hexagonal Cu-2 Te has been synthesised by mechanical alloying from elemental powders. The milling time required for the synthesis is longer than that reported for other tellurides. The mechanical grinding of the bulk Cu2Te obtained by the melting route does not change the structure. Prolonged milling as well as grinding beyond 40 h lead to a decrease in grain size to nanometer level. The cold compaction of milled or ground powders exhibit much smaller Seebeck coefficient (thermopower). However, cold compaction of samples milled for longer time (>150 h) lead to the thermopower values close to that of the bulk indicating significant improvement of rheological properties at room temperature for powders milled for long times.

K. Sridhar

Papers

Synthesis by mechanical alloying and thermoelectric properties of Cu2Te

Synthesis by Mechanical Alloying and Thermoelectric Properties of Cu2Te.