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      Thermoelectric Properties of Highly-Crystallized Ge-Te-Se Glasses Doped with Cu/Bi

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          Abstract

          Chalcogenide semiconducting systems are of growing interest for mid-temperature range (~500 K) thermoelectric applications. In this work, Ge 20Te 77Se 3 glasses were intentionally crystallized by doping with Cu and Bi. These effectively-crystallized materials of composition (Ge 20Te 77Se 3) 100− x M x (M = Cu or Bi; x = 5, 10, 15), obtained by vacuum-melting and quenching techniques, were found to have multiple crystalline phases and exhibit increased electrical conductivity due to excess hole concentration. These materials also have ultra-low thermal conductivity, especially the heavily-doped (Ge 20Te 77Se 3) 100− x Bi x ( x = 10, 15) samples, which possess lattice thermal conductivity of ~0.7 Wm −1 K −1 at 525 K due to the assumable formation of nano-precipitates rich in Bi, which are effective phonon scatterers. Owing to their high metallic behavior, Cu-doped samples did not manifest as low thermal conductivity as Bi-doped samples. The exceptionally low thermal conductivity of the Bi-doped materials did not, alone, significantly enhance the thermoelectric figure of merit, zT. The attempt to improve the thermoelectric properties by crystallizing the chalcogenide glass compositions by excess doping did not yield power factors comparable with the state of the art thermoelectric materials, as these highly electrically conductive crystallized materials could not retain the characteristic high Seebeck coefficient values of semiconducting telluride glasses.

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          Complex thermoelectric materials.

          Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching. We review recent advances in the field, highlighting the strategies used to improve the thermopower and reduce the thermal conductivity.
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            Recent advances in magnetic structure determination by neutron powder diffraction

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              Thin-film thermoelectric devices with high room-temperature figures of merit.

              Thermoelectric materials are of interest for applications as heat pumps and power generators. The performance of thermoelectric devices is quantified by a figure of merit, ZT, where Z is a measure of a material's thermoelectric properties and T is the absolute temperature. A material with a figure of merit of around unity was first reported over four decades ago, but since then-despite investigation of various approaches-there has been only modest progress in finding materials with enhanced ZT values at room temperature. Here we report thin-film thermoelectric materials that demonstrate a significant enhancement in ZT at 300 K, compared to state-of-the-art bulk Bi2Te3 alloys. This amounts to a maximum observed factor of approximately 2.4 for our p-type Bi2Te3/Sb2Te3 superlattice devices. The enhancement is achieved by controlling the transport of phonons and electrons in the superlattices. Preliminary devices exhibit significant cooling (32 K at around room temperature) and the potential to pump a heat flux of up to 700 W cm-2; the localized cooling and heating occurs some 23,000 times faster than in bulk devices. We anticipate that the combination of performance, power density and speed achieved in these materials will lead to diverse technological applications: for example, in thermochemistry-on-a-chip, DNA microarrays, fibre-optic switches and microelectrothermal systems.
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                Author and article information

                Affiliations
                [1 ]Équipe Verres et Céramiques, ISCR CNRS UMR 6226, Université de Rennes 1, Rennes 35042, France; bhuvanesh.srinivasan@ 123456univ-rennes1.fr (B.S.); catherine.boussard@ 123456univ-rennes1.fr (C.B.-P.); francois.chevire@ 123456univ-rennes1.fr (F.C.)
                [2 ]PRATS, ISCR CNRS UMR 6226, Université de Rennes 1, Rennes 35042, France; vincent.dorcet@ 123456univ-rennes1.fr
                [3 ]New Chemistry Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064, India; manishas@ 123456jncasr.ac.in (M.S.); kanishka@ 123456jncasr.ac.in (K.B.)
                [4 ]ENSICAEN, UNICAEN, CNRS, IUT-Caen, CRISMAT, Normandie Université, Caen 14050, France; robin.lefevre@ 123456ensicaen.fr (R.L.); franck.gascoin@ 123456ensicaen.fr (F.G.)
                [5 ]Institut de Physique de Rennes, CNRS UMR 6251-Université de Rennes 1, Rennes 35042, France; sylvain.tricot@ 123456univ-rennes1.fr
                [6 ]School of Engineering and Materials Science, Queen Mary University of London, London E1 4NS, UK; m.j.reece@ 123456qmul.ac.uk
                Author notes
                [* ]Correspondence: bruno.bureau@ 123456univ-rennes1.fr ; Tel.: +33-223-236-573; Fax: +33-223-235-611
                Contributors
                Role: Academic Editor
                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                MDPI
                1996-1944
                23 March 2017
                April 2017
                : 10
                : 4
                5506923 10.3390/ma10040328 materials-10-00328
                © 2017 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

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