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Bertrand Lenoir

Bio: Bertrand Lenoir is an academic researcher from University of Lorraine. The author has contributed to research in topics: Thermoelectric effect & Seebeck coefficient. The author has an hindex of 31, co-authored 202 publications receiving 3677 citations. Previous affiliations of Bertrand Lenoir include University of Rennes & Mines ParisTech.


Papers
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TL;DR: In this article, the authors evaluated the thermoelectric performance of polycrystalline p-type SnSe, a material in which unprecedented values of the thermoclectric figure of merit ZT have been recently discovered in single crystals.
Abstract: We report the evaluation of the thermoelectric performance of polycrystalline p-type SnSe, a material in which unprecedented values of the thermoelectric figure of merit ZT have been recently discovered in single crystals Besides anisotropic transport properties, our results confirm that this compound exhibits intrinsically very low thermal conductivity values The electrical properties show trends typical of lightly doped, intrinsic semiconductors with thermopower values reaching 500 μV K−1 in a broad temperature range An orthorhombic-to-orthorhombic transition sets in at 823 K, a temperature at which the power factor reaches its maximum value A maximum ZT of 05 was obtained at 823 K, suggesting that proper optimization of the transport properties of SnSe might lead to higher ZT values These findings indicate that this system represents an interesting experimental platform for the search of highly efficient thermoelectric materials

310 citations

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TL;DR: In this paper, the authors focused on the investigation of the transport properties of BiSb alloys and measured electrical resistivity, thermoelectric power and thermal conductivity in a direction perpendicular or parallel to the trigonal axis within the temperature range 4.2 - 300 K on various alloy compositions containing up to 18.2 at.

227 citations

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TL;DR: In this article, the temperature dependences of the electrical resistivity, Seebeck coefficient, and thermal conductivity have been measured on these compounds in the 300-800 K temperature range and they identified Ca as being a true n-type filler atom and offer, for this family of skutterudite, several valuable insights into the potential of Ca to provide good thermoelectric performance.
Abstract: Partially filled CoSb3 skutterudite compounds are emerging materials for thermoelectric energy conversion at high temperature. CaxCo4Sb12 with different Ca contents has been prepared by the conventional metallurgical route. The temperature dependences of the electrical resistivity, Seebeck coefficient, and thermal conductivity have been measured on these compounds in the 300–800 K temperature range. These measurements have identified Ca as being a true n-type filler atom and offer, for this family of skutterudite, several valuable insights into the potential of Ca to provide good thermoelectric performance.

154 citations

Journal ArticleDOI
TL;DR: In this article, the electrical resistivity, thermoelectric power and thermal conductivity have been measured between 4.2 and 300 K on three Bi1−xSbx alloys of different composition (x = 0.144, 0.165 and 0.181).

102 citations

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TL;DR: The mechanism in which glass-like thermal conductivity emerges in tetrahedrites, a family of natural minerals extensively studied in geology and, more recently, in thermoelectricity, is unveiled.
Abstract: The ability of some materials with a perfectly ordered crystal structure to mimic the heat conduction of amorphous solids is a remarkable physical property that finds applications in numerous areas of materials science, for example, in the search for more efficient thermoelectric materials that enable to directly convert heat into electricity. Here, we unveil the mechanism in which glass-like thermal conductivity emerges in tetrahedrites, a family of natural minerals extensively studied in geology and, more recently, in thermoelectricity. By investigating the lattice dynamics of two tetrahedrites of very close compositions (Cu12Sb2Te2S13 and Cu10Te4S13) but with opposite glasslike and crystal thermal transport by means of powder and single-crystal inelastic neutron scattering, we demonstrate that the former originates from the peculiar chemical environment of the copper atoms giving rise to a strongly anharmonic excess of vibrational states.

90 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, it was shown that the parity of the occupied Bloch wave functions at the time-reversal invariant points in the Brillouin zone greatly simplifies the problem of evaluating the topological invariants.
Abstract: Topological insulators are materials with a bulk excitation gap generated by the spin-orbit interaction that are different from conventional insulators. This distinction is characterized by ${Z}_{2}$ topological invariants, which characterize the ground state. In two dimensions, there is a single ${Z}_{2}$ invariant that distinguishes the ordinary insulator from the quantum spin-Hall phase. In three dimensions, there are four ${Z}_{2}$ invariants that distinguish the ordinary insulator from ``weak'' and ``strong'' topological insulators. These phases are characterized by the presence of gapless surface (or edge) states. In the two-dimensional quantum spin-Hall phase and the three-dimensional strong topological insulator, these states are robust and are insensitive to weak disorder and interactions. In this paper, we show that the presence of inversion symmetry greatly simplifies the problem of evaluating the ${Z}_{2}$ invariants. We show that the invariants can be determined from the knowledge of the parity of the occupied Bloch wave functions at the time-reversal invariant points in the Brillouin zone. Using this approach, we predict a number of specific materials that are strong topological insulators, including the semiconducting alloy ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ as well as $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ and HgTe under uniaxial strain. This paper also includes an expanded discussion of our formulation of the topological insulators in both two and three dimensions, as well as implications for experiments.

3,349 citations

Journal ArticleDOI
24 Apr 2008-Nature
TL;DR: In this article, the authors used incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES) to locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands.
Abstract: When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic fields. Bulk Bi(1-x)Sb(x) single crystals are predicted to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher-dimensional analogues of the edge states that characterize a quantum spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi(1-x)Sb(x) is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest following the new findings in two-dimensional graphene and charge quantum Hall fractionalization observed in pure bismuth. However, despite numerous transport and magnetic measurements on the Bi(1-x)Sb(x) family since the 1960s, no direct evidence of either topological Hall states or bulk Dirac particles has been found. Here, using incident-photon-energy-modulated angle-resolved photoemission spectroscopy (IPEM-ARPES), we report the direct observation of massive Dirac particles in the bulk of Bi(0.9)Sb(0.1), locate the Kramers points at the sample's boundary and provide a comprehensive mapping of the Dirac insulator's gapless surface electron bands. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the 'topological metal'. They also suggest that this material has potential application in developing next-generation quantum computing devices that may incorporate 'light-like' bulk carriers and spin-textured surface currents.

2,739 citations

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TL;DR: The most promising bulk materials with emphasis on results from the last decade are described and the new opportunities for enhanced performance bulk nanostructured composite materials are examined and a look into the not so distant future is attempted.
Abstract: Herein we cover the key concepts in the field of thermoelectric materials research, present the current understanding, and show the latest developments. Current research is aimed at increasing the thermoelectric figure of merit (ZT) by maximizing the power factor and/or minimizing the thermal conductivity. Attempts at maximizing the power factor include the development of new materials, optimization of existing materials by doping, and the exploration of nanoscale materials. The minimization of the thermal conductivity can come through solid-solution alloying, use of materials with intrinsically low thermal conductivity, and nanostructuring. Herein we describe the most promising bulk materials with emphasis on results from the last decade. Single-phase bulk materials are discussed in terms of chemistry, crystal structure, physical properties, and optimization of thermoelectric performance. The new opportunities for enhanced performance bulk nanostructured composite materials are examined and a look into the not so distant future is attempted.

1,951 citations

Journal ArticleDOI
TL;DR: In this paper, the authors introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions.
Abstract: Thermoelectrics have long been recognized as a potentially transformative energy conversion technology due to their ability to convert heat directly into electricity. Despite this potential, thermoelectric devices are not in common use because of their low efficiency, and today they are only used in niche markets where reliability and simplicity are more important than performance. However, the ability to create nanostructured thermoelectric materials has led to remarkable progress in enhancing thermoelectric properties, making it plausible that thermoelectrics could start being used in new settings in the near future. Of the various types of nanostructured materials, bulk nanostructured materials have shown the most promise for commercial use because, unlike many other nanostructured materials, they can be fabricated in large quantities and in a form that is compatible with existing thermoelectric device configurations. The first generation of these materials is currently being developed for commercialization, but creating the second generation will require a fundamental understanding of carrier transport in these complex materials which is presently lacking. In this review we introduce the principles and present status of bulk nanostructured materials, then describe some of the unanswered questions about carrier transport and how current research is addressing these questions. Finally, we discuss several research directions which could lead to the next generation of bulk nanostructured materials.

1,742 citations