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2. Influence of SnBiAntisite Defects on the Electronic Band Structure and Transport Properties of the Layered Chalcogenide Semiconductor SnBi2Te4

Author

Terzi, Ilayda, Pryga, Kacper, Wiendlocha, Bartlomiej, Levinský, Petr, El Oualid, Soufiane, Migot, Sylvie, Ghanbaja, Jaafar, Gendarme, Christine, Schweitzer, Thierry, Malaman, Bernard, Le Caër, Gérard, Lenoir, Bertrand, and Candolfi, Christophe

Abstract

Narrow-band gap, layered chalcogenide semiconductors provide a rich area of research for designing highly efficient thermoelectric materials for near-room-temperature applications due to their intrinsically low lattice thermal conductivity and multivalley electronic band structure. Here, we report on a comprehensive theoretical and experimental investigation of the thermoelectric properties of one member of this class, SnBi2Te4, in the temperature range of 5–700 K. Polycrystalline samples crystallize with a rhombohedral crystal structure described in the R3̅mspace group (No. 166) with room-temperature lattice parameters a= 4.398(1) and c= 41.615(1) Å. To probe the electronic tunability of SnBi2Te4, the synthesis of a Sn-deficient sample Sn0.95Bi2Te4was attempted but led to an intergrowth of SnBi2Te4and SnBi4Te7, indicating that only a very limited range of Sn-deficiency can exist. Transport property measurements combined with electronic band structure calculations show that SnBi2Te4is a p-type, narrow-band gap semiconductor with a multivalley valence band structure and a strong asymmetry between the valence and conduction bands. The presence of SnBiantisite defects, supported by Mössbauer spectroscopy, plays an important role in shaping the electronic transport properties through a decrease in the electronic band gap and a reduction in the hole mobility, which causes the onset of bipolar conduction near 350 K. Some degree of anisotropy in the electrical resistivity and thermal conductivity measured parallel and perpendicular to the pressing direction exists, while the thermopower remains nearly isotropic. The complex crystal structure of SnBi2Te4contributes to the very low lattice thermal conductivity of the order of 0.5 W m–1K–1at 300 K, leading to peak ZTvalues of 0.32 at 350 and 400 K for Sn0.95Bi2Te4and SnBi2Te4, respectively.

Published
2024
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6. Magnetic structures of Mn-rich and of Fe-rich TmMn 6 − x Fe x Sn 6 stannides with (Mn, Fe) kagome networks and related 119Sn hyperfine magnetic fields

Author

Venturini, G., Malaman, B., Le Caër, Gérard, Mazet, T., Institut Jean Lamour (IJL), Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Lorraine (UL)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)

Subjects
PACS numbers: 75.25.+z, PACS numbers: 71.20.Lp, PACS numbers: 76.80.+y † deceased, [CHIM.MATE]Chemical Sciences/Material chemistry, [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat], PACS numbers: 33.45+x
Abstract

International audience; Stannides TmMn6-xFexSn6, with hexagonal HfFe6Ge6-type structures, were studied by X-ray and neutron diffraction, magnetic measurements and by 119Sn Mössbauer spectroscopy. Transition metal atoms form kagome networks in (001) planes with an intraplanar ferromagnetic coupling of their moments. At temperatures higher than ~ 20 to 50 K, Mn-rich stannides, (x = 0.4, 0.6, 1.2), have an AFII easy-plane antiferromagnetic structure, with interplanar couplings ++-- along the c-axis. The thulium sublattice orders magnetically at low temperature. The complexity of the resultant neutron diffraction patterns arises from a mixture of several magnetic phases, some being incommensurate. The Tm sublattice does not order above 1.6 K in Fe-rich stannides (x = 4.25, 4.5, 5.0). Fe-rich stannides have an AFI antiferromagnetic structure, this time with interplanar couplings +-+-. The M = Mn/Fe magnetic moments are directed along the c-axis for x=5 at any temperature. Further, neutron diffraction shows that moments rotate from the c-axis towards the basal plane above 4.2 K with maximum rotation angles of ~70° and of ~55° reached at ~50 K and ~80 K for x = 4.25 and 4.50 respectively. Transferred hyperfine fields at tin sites of TmMn6-xFexSn6 stannides are the moduli of 119Sn vectorial hyperfine magnetic fields that are modelled for the AFI and AFII magnetic structures assuming a random substitution of Mn with Fe. Models involve sums of dipolar-type and of isotropic vector components, with simple assumptions about the model parameters. The transferred hyperfine magnetic fields at 119Sn nuclei are measured by Mössbauer spectroscopy. The hyperfine magnetic fields of Sn atoms, whose six transitionmetal nearest neighbors are ferromagnetically coupled, are predicted and observed to vary linearly with their number of Fe first nearest neighbors. The hyperfine magnetic fields on Sn atoms sandwiched between two antiferromagnetically-coupled kagome planes are expected proportional to abs(p2-p1) , where one of the two kagome planes contains p1 Fe first nearest neighbor and the other p2 . Tin atoms, with a ferromagnetic first nearest neighbor shell, experience negative hyperfine fields in Mn-rich stannides whereas they experience positive hyperfine fields in the Fe-rich stannides. This change is explained by a change of sign of the isotropic hyperfine magnetic fields which occurs when going fom Mn-rich to Fe-rich stannides.

Published
2021
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9. Disorder-driven glasslike thermal conductivity in colusite Cu26V2Sn6S32 investigated by Mössbauer spectroscopy and inelastic neutron scattering

Author

Candolfi, Christophe, Guélou, Gabin, Bourgès, Cédric, Supka, Andrew, Al Rahal Al Orabi, Rabih, Fornari, Marco, Malaman, Bernard, Le Caër, Gérard, Lemoine, Pierric, Hardy, Vincent, Zanotti, Jean-Marc, Chetty, Raju, Ohta, Michihiro, Suekuni, Koichiro, Guilmeau, Emmanuel, Institut Jean Lamour (IJL), Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de cristallographie et sciences des matériaux (CRISMAT), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche sur les Matériaux Avancés (IRMA), Normandie Université (NU)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Institut national des sciences appliquées Rouen Normandie (INSA Rouen Normandie), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Rouen Normandie (UNIROUEN), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS), Central Michigan University (CMU), Solvay (France), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), LLB - Matière molle et biophysique (MMB), Laboratoire Léon Brillouin (LLB - UMR 12), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Tsukuba = University of Tsukuba, National Institute of Advanced Industrial Science and Technology (AIST), Kyushu University, U.S. Department of Defense, N000141310635, Office of Naval Research, Ministry of Economy, Trade and Industry, ANR-15-CE05-0027,MASSCOTE,Matériaux Sulfures à Structures Complexes: application à la Thermoélectricité(2015), Université de Lorraine (UL)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Normandie Université (NU)-Centre National de la Recherche Scientifique (CNRS)-Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Institut de Chimie du CNRS (INC), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay, Kyushu University [Fukuoka], Agence Nationale de la Recherche, Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Normandie Université (NU)-Université de Caen Normandie (UNICAEN), Normandie Université (NU), Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Supérieure de Chimie de Rennes-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay, University of Tsukuba, and National Institute for Advanced Industrial Science and Technology - AIST (JAPAN)

Subjects
[PHYS]Physics [physics], Thermal properties, Mössbauer spectroscopy, Time-of-flight neutron spectroscopy, Polycrystalline materials, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [CHIM]Chemical Sciences, [CHIM.MATE]Chemical Sciences/Material chemistry
Abstract

International audience; The influence of structural disorder on the thermal transport in the colusite Cu26V2Sn6S32 has been investigated by means of low-temperature thermal conductivity and specific heat measurements (2–300 K), 119Sn Mössbauer spectroscopy and temperature-dependent powder inelastic neutron scattering (INS). Variations in the high-temperature synthesis conditions act as a key parameter for tuning the degree of disorder in colusite compounds. Intriguingly, we find that all synthesized samples are disordered, the degree of which varies with the synthesis conditions used. Mössbauer data clearly evidence that Sn atoms do not solely occupy the 6c site of the crystal lattice but are present on possibly both the Cu and V sites, leading to a random distribution of these three cations within the unit cell. Increasing the disorder in these materials tends to lead to a smearing out of the main features in the phonon density of states measured by INS. Although the evolution of the inelastic signal upon warming is well described by a quasiharmonic approximation, elastic properties calculations indicate large average Grüneisen parameters, consistent with those determined experimentally from thermodynamic data. Increasing the level of disorder results in a decreased average Grüneisen parameter suggesting that the lowered lattice thermal conductivity is not driven by enhanced anharmonicity. These results provide experimental evidence to support that the remarkable changeover in the lattice thermal conductivity from crystalline to glasslike is solely driven by enhanced disorder accompanied by local lattice distortions.

Published
2020
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10. Comprehensive study of the low-temperature transport properties of polycrystalline Sn1+xTe (x = 0 and 0.03)

Author

Ibrahim, Dorra, Candolfi, Christophe, Migot, Sylvie, Ghanbaja, Jaafar, Dauscher, Anne, Le Caër, Gérard, Malaman, Bernard, Semprimoschnig, Christopher, Lenoir, Bertrand, Institut Jean Lamour (IJL), Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), European Space Research and Technology Centre (ESTEC), Agence Spatiale Européenne = European Space Agency (ESA), European Space Agency under NPI [40001134346/15/NL/RA], and Region Lorraine - Region Grand-Est [2015-9337]

Subjects
[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph]
Abstract

International audience; We report a detailed investigation of the low-temperature transport properties (5-300 K) on polycrystalline samples of Sn1+xTe (x = 0 and 0.03) prepared by melt quenching in water and slow cooling. These two different synthetic routes result in variations in the hole concentration over more than one order of magnitude, allowing for a systematic investigation of the influence of Sn vacancies on the transport properties. The results evidence a strong correlation between the details of the synthetic process and the concentration of Sn vacancies. Transmission electron microscopy and Mossbauer spectroscopy show that the excess Sn, which helps to lower the hole concentration, segregates at grain boundaries. Interestingly, Hall-effect measurements reveal that charge transport is dominated near 300 K by alloy scattering regardless of the hole concentration. In addition to dictating the electronic properties, the concentration of Sn vacancies has also a significant impact on the thermal transport, with the magnitude of the low-temperature Umklapp peak observed in the lattice thermal conductivity near 30 K scaling with the concentration of Sn vacancies that act as efficient point-defect scatterers.

Published
2019
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17. Neutron powder diffraction and Mössbauer spectroscopy (119Sn and 155Gd) studies of the CeScSi-type GdMgSn and GdMgPb compounds

Author

Lemoine , P., Lee-Hone , Nicolas, Ryan , D. H., Vernière , A., Malaman , Bernard, Le Caër , Gérard, Department of physics and astronomy [Winnipeg], University of Manitoba [Winnipeg], Institut Jean Lamour ( IJL ), Université de Lorraine ( UL ) -Centre National de la Recherche Scientifique ( CNRS ), McGill University, Institut de Physique de Rennes ( IPR ), Université de Rennes 1 ( UR1 ), Université de Rennes ( UNIV-RENNES ) -Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ), Institut Jean Lamour (IJL), Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), McGill University = Université McGill [Montréal, Canada], Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
75.25.−j, 61.05.fm, 76.80.+y, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [ PHYS.COND.CM-MS ] Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [ CHIM.INOR ] Chemical Sciences/Inorganic chemistry, [CHIM.INOR]Chemical Sciences/Inorganic chemistry
Abstract

International audience; The magnetic structures of the CeScSi-type GdMgSn and GdMgPb compounds have been studied by both neutron powder diffraction and Mössbauer spectroscopy (119Sn and 155Gd). The neutron diffraction results show that the two compounds adopt incommensurate antiferromagnetic structures at 5.4 K with propagation vectors k⃗ =[0.910,0.077,0] for GdMgSn and k⃗ =[0.892,0,0] for GdMgPb. The magnetic moments lie in the basal plane, which is confirmed by both 119Sn and 155Gd Mössbauer spectroscopy. Mössbauer spectroscopy refinements and simulations reveal that the magnetic structure of GdMgSn is cycloidal at low temperature and undergoes a transition to a modulated magnetic structure above T∼40 K. A similar magnetic transition is inferred for GdMgPb. The magnetic structures of GdMgSn and GdMgPb are compared with those of other CeScSi-type compounds.

Published
2014
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18. Lipid Packing Sensitivity of Exchangeable Apolipoproteins apoA-I and apoA-II

Author

Chièze, Lionel, Bolanos-Garcia, V., Le Caër, Gérard, Renault, Anne, Desbat, B., Vié, Véronique, Beaufils, Sylvie, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), and Cadieu, Muriel

Subjects
[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft], [PHYS.COND.CM-SCM] Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft]
Published
2012

19. Designing a Thermoelectric Copper-Rich Sulfide from a Natural Mineral: Synthetic Germanite Cu22Fe8Ge4S32

Author

Pavan Kumar, Ventrapati, Paradis-Fortin, Laura, Lemoine, Pierric, Caignaert, Vincent, Raveau, Bernard, Malaman, Bernard, Le Caër, Gérard, Cordier, Stéphane, and Guilmeau, Emmanuel

Abstract

This study shows that the design of copper-rich sulfides by mimicking natural minerals allows a new germanite-type sulfide Cu22Fe8Ge4S32with promising thermoelectric properties to be synthesized. The Mössbauer spectroscopy and X-ray diffraction analyses provide evidence that the structure of our synthetic compound differs from that of the natural germanite mineral Cu26Fe4Ge4S32by its much higher Cu+/Cu2+ratio and different cationic occupancies. The coupled substitution Cu/Fe in the Cu26–xFe4+xGe4S32series also appears as a promising approach to optimize the thermoelectric properties. The electrical resistivity, which decreases slightly as the temperature increases, shows that these materials exhibit a semiconducting behavior, but are at the border of a metallic state. The magnitudes of the electrical resistivity and Seebeck coefficient increase with x, which suggests that Fe for Cu substitution decreases the hole concentration. The thermal conductivity decreases as the temperature increases leading to a moderately low value of 1.2 W m–1K–1and a maximum ZT value of 0.17 at 575 K.

Published
2024
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21. Experimental Evidence of Aging and Memory Effects in Inclined 3D Granular Packings

Author

Delannay, Renaud, Kiesgen de Richter, Sébastien, Le Caër, Gérard, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Delannay, Renaud, and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.COND.CM-GEN] Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other], [PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2010

22. Ball Milling of an Equiatomic sigma-FeV Alloy in Vacuum

Author

Costa, B. F. O., Le Caër, Gérard, Department of Physics (CEMDRX), University of Coimbra [Portugal] (UC), Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)

Subjects
General Relativity and Quantum Cosmology, Condensed Matter::Materials Science, [PHYS.PHYS.PHYS-GEN-PH]Physics [physics]/Physics [physics]/General Physics [physics.gen-ph]
Abstract

WOS:000273984900091; International audience; A coarse-grained tetragonal sigma phase Fe(47.4)V(52.6) at% alloy was ground in vacuum in a vibratory mill. The sigma phase transforms into a bcc alpha phase. A concomitant partial amorphization of the bcc phase occurs. The near-equiatomic FeV alloys are concluded to behave in the same way as the related FeCr alloys when they are ball-milled in vacuum in similar milling conditions. In the stationary state of milling, about half of the iron atoms are contained in an amorphous phase both for sigma-FeCr and for sigma-FeV.

Published
2010
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23. Ball-milling in vacuum of [alpha] and [sigma] phases of near-equiatomic FeCr alloys

Author

Costa, Benilde F. O., Le Caër, Gérard, Loureiro, J. M., Groupe matière condensée et matériaux (GMCM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Brébion, Alice, and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Amorphisation, Mössbauer spectroscopy, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], [sigma]-Phase, [alpha]-Phase, [PHYS.COND.CM-MS] Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], Ball-milling
Abstract

http://www.sciencedirect.com/science/article/B6TWY-4V34RFW-N/2/c9147c3fe84413d6b8e8875146fc1b0b

Published
2009

24. The δn statistic for the β-Hermite ensemble

Author

Le Caër, Gérard, Male, Camille, Delannay, Renaud, Granulaires - Mousses, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Unité de Mathématiques Pures et Appliquées (UMPA-ENSL), École normale supérieure de Lyon (ENS de Lyon)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), and École normale supérieure - Lyon (ENS Lyon)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Random matrix theory, Nearest-neighbor spacing, Simple logarithmic behavior
Abstract

International audience; The fluctuation δn of the nth unfolded eigenvalue was recently characterized for the classical Gaussian ensembles of N×N random matrices (GOE, GUE, GSE). It is investigated here for the β-Hermite ensemble as a function of the reciprocal of the temperature β by Monte Carlo simulations. The ensemble-averaged fluctuation and the autocorrelation function vary logarithmically with n for any β>0 (1≪n≪N). The simple logarithmic behavior of the higher-order moments of δn, reported in the literature for the GOE (β=1) and the GUE (β=2), holds for any β>0 and is accounted for by Gaussian distributions whose variances depend linearly on lnn.

Published
2008
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25. Local fluctuations of eigenvalues of random matrices from the beta-Hermite ensemble

Author

Le Caër, Gérard, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Brébion, Alice, and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.PHYS.PHYS-DATA-AN] Physics [physics]/Physics [physics]/Data Analysis, Statistics and Probability [physics.data-an], ComputingMilieux_MISCELLANEOUS, [PHYS.PHYS.PHYS-DATA-AN]Physics [physics]/Physics [physics]/Data Analysis, Statistics and Probability [physics.data-an]
Abstract

International audience

Published
2008

26. Erratum to 'Nearest-neighbour spacing distributions of the -Hermite ensemble of random matrices' [Physica A 383 (2007) 190–208]

Author

Le Caër, Gérard, Male, C., Delannay, Renaud, Institut de Physique de Rennes (IPR), Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Probabilités et Modèles Aléatoires (LPMA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Université de Rennes 1 (UR1), and Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[MATH.MATH-PR]Mathematics [math]/Probability [math.PR], [PHYS.MPHY]Physics [physics]/Mathematical Physics [math-ph], ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2008
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27. Mechanically-activated solid-state synthesis of nanoparticles of HfB2, HfC and HfN from partially hydrated hafnium tetrachloride

Author

Barraud, Elodie, Bégin-Colin, Sylvie, Le Caër, Gérard, Barres, Odile, Villiéras, Frédéric, Laboratoire de Science et Génie des Matériaux et de Métallurgie (LSG2M), Université Henri Poincaré - Nancy 1 (UHP)-Institut National Polytechnique de Lorraine (INPL)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Université de Strasbourg (UNISTRA)-Matériaux et nanosciences d'Alsace (FMNGE), Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA), Granulaires - Mousses, Institut de Physique de Rennes (IPR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Environnement et Minéralurgie (LEM), Institut National Polytechnique de Lorraine (INPL)-Centre National de la Recherche Scientifique (CNRS), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Matériaux et Nanosciences Grand-Est (MNGE), Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
carbides, solid state synthesis, nitrides, nanotechnology, heat treatment, ceramics, mechanochemical processing, mechanical alloying, leaching, hafnium tetrachloride, borides, nanostructures, nanoparticles, infrared spectroscopy, thermal analysis
Abstract

International audience; Nanocrystalline hafnium diboride, carbide and nitride are synthesised by a two-step process, namely a short mechanical activation step (∼1?2 h) of powder mixtures based on partially hydrated hafnium tetrachloride, ph-HfCl4, and on magnesium, followed by a brief annealing step (∼1 h) of the activated powders in flowing argon at 1100?C. HfCl4 is a by-product of the carbochlorination process of extraction of zirconium from ores. Magnesium has a strong reducing capacity and is insoluble in metallic hafnium. The unsought reaction products may then be eliminated during the additional heat treatment or by further leaching. Mechanically activated powder mixtures of ph-HfCl4 + B and of ph-HfCl4 + B + Mg yield either facetted grains or monocrystalline rods of HfB2 according to the composition of the initial mixtures and to the temperature and duration of the annealing treatment. The mean size of the facetted grains ranges between 100 nm and 300 nm. The growth direction of the rods is along the c-axis. Their mean diameters are around 100 nm and their mean lengths are in the range 500 nm?1 um. Hafnium carbide HfC is directly mechanosynthesised from ph-HfCl4 + Mg + C powder mixtures. A subsequent heat treatment in flowing argon allows to better crystallise the grains of HfC (∼100 nm) and to decompose the intermediate products. Annealing of ground ph-HfCl4 + Mg blends in flowing nitrogen for 1 h at 1100?C yields HfN nanoparticles whose size ranges between 10 nm and 30 nm. Characterisations of powders by X-ray diffraction, thermogravimetric analysis, scanning and transmission electron microscopy, Fourier Transform Infrared Spectroscopy were performed to follow the phase evolution and to clarify the reaction mechanisms.

Published
2008
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28. 1/fα noise in the fluctuations of the spectra of tridiagonal random matrices from the beta-Hermite ensemble

Author

Male, Camille, Le Caër, Gérard, Delannay, Renaud, Groupe matière condensée et matériaux (GMCM), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[PHYS.COND.CM-SCM]Physics [physics]/Condensed Matter [cond-mat]/Soft Condensed Matter [cond-mat.soft]
Abstract

International audience; The 1∕fα noise displayed by the fluctuation of the nth unfolded eigenvalue, where n plays the role of a discrete time, was recently characterized for the classical Gaussian ensembles of N×N random matrices. It is investigated here for the β-Hermite ensemble by wavelet analysis of Monte Carlo simulated series both as a function of β and of N. When β decreases from 1 to 0, for a given and large enough N, the evolution from a 1∕f noise at β=1 Gaussian orthogonal ensemble (GOE) to a 1∕f2 noise at β=0 Gaussian diagonal ensemble (GDE) is heterogeneous with a ∼1∕f2 noise at the finest scales and a ∼1∕f noise at the coarsest ones.

Published
2007
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29. Thermal decomposition of HfCl4 as a function of its hydration state

Author

Barraud, E., Bégin, S., Le Caër, Gérard, Villieras, F., Barres, O., Masson, Beatrice, Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), and Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS)

Published
2006

31. Mössbauer spectrometry of near equiatomic Fe-Cr alloys: Phase separation at high temperature?

Author

Le Caër, Gérard, Delcroix, P., Costa, Benilde F. O., Groupe matière condensée et matériaux (GMCM), Centre National de la Recherche Scientifique (CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Laboratoire de Science et Génie des Matériaux et de Métallurgie (LSG2M), Université Henri Poincaré - Nancy 1 (UHP)-Institut National Polytechnique de Lorraine (INPL)-Centre National de la Recherche Scientifique (CNRS), and Université de Rennes (UR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Hyperfine interactions, Mössbauer spectroscopy, [PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci], Metals and alloys
Abstract

International audience; Mössbauer spectrometry shows that a bulk bcc Fe0.51Cr0.49 alloy annealed between 1000 and 1200 °C and quenched at ambient temperature is not phase-separated in contradiction with recent claims. Despite small differences in the various hyperfine magnetic field distributions, none shows the features expected for phase separation. The latter differences, which are discussed in a companion paper, reflect the sensitivity of the Fe-Cr chemical order to the alloy treatments.

Published
2005
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35. Measurement of granular entropy

Author

McNamara, Sean, primary, Richard, Patrick, additional, de Richter, Sébastien Kiesgen, additional, Le Caër, Gérard, additional, and Delannay, Renaud, additional

Published
2009
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36. On the Origin of the Decay of the Photocatalytic Activity of TiO2 Powders Ground at High Energy

Author

Bégin-Colin, Sylvie, primary, Gadalla, Atef, additional, Le Caër, Gérard, additional, Humbert, Olivier, additional, Thomas, Fabien, additional, Barres, Odile, additional, Villiéras, Frédéric, additional, Toma, Laura F., additional, Bertrand, Ghislaine, additional, Zahraa, Orfan, additional, Gallart, Matthieu, additional, Hönerlage, Bernd, additional, and Gilliot, Pierre, additional

Published
2009
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38. Some recent developments in mechanical activation and mechanosynthesis

Author

Gaffet, Eric, primary, Bernard, Frédéric, additional, Niepce, Jean-Claude, additional, Charlot, Frédéric, additional, Gras, Christophe, additional, Le Caër, Gérard, additional, Guichard, Jean-Louis, additional, Delcroix, Pierre, additional, Mocellin, Alain, additional, and Tillement, Olivier, additional

Published
1999
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47. 71Ga NMR in chalcogenide and chalco-halide glasses.

Author

Ledemi, Yannick, Bureau, Bruno, Le Caër, Gérard, Calvez, Laurent, Roiland, Claire, Tricot, Grégory, Florian, Pierre, Nazabal, Virginie, and Massiot, Dominique

Subjects
*SEMICONDUCTOR doped glasses, *NUCLEAR magnetic resonance, *GALLIUM, *COVALENT bonds, *ELECTRIC fields, *ION exchange (Chemistry)
Abstract

Abstract: Chalcogenide and chalco-halide glasses containing gallium have been studied through 71Ga solid state nuclear magnetic resonance (NMR). An unusual line shape of the 71Ga NMR spectra has been observed for the first time. This line shape was ascribed to the preferential local symmetry existing around gallium atoms in these glasses which are characterized by the covalent character of their chemical bonds. Then, the local environment of gallium in Ga2S3–GeS2–CsCl glasses was studied by 71Ga NMR as a function of the ionic cesium chloride CsCl concentration. In this system, CsCl directly interacts with Ga by forming anionic complexes, modifying its environment. The Czjzek's electric field gradient distribution and its recent extension have been successfully applied to reconstruct the experimental 71Ga NMR spectra. These results highlight the evolution of local surroundings of Ga atoms in the glass network as a function of the CsCl concentration. [Copyright &y& Elsevier]

Published
2014
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48. An extension of the Czjzek model for the distributions of electric field gradients in disordered solids and an application to NMR spectra of 71Ga in chalcogenide glasses.

Author

Le Caër G, Bureau B, and Massiot D

Abstract

First, the basis and the characteristics of the Czjzek model for the distribution of electric field gradient (EFG) tensor in disordered solids, some of which are still unnoticed, are depicted. That model results from the statistical invariance by rotation of the structure of the considered disordered solid and from the applicability of a central limit theorem to the EFG tensor. These two conditions, which are physically realistic for a wealth of disordered solids, simplify tremendously the derivation of the EFG distribution but at the cost of a complete loss of structural information about the investigated solid. Next, we describe a simple extension of it which is intended to mimic a well-defined local environment, with given values of the asymmetry parameter and of the principal component Vzz of the EFG tensor, perturbed by the disorder of more remote atoms. The effect of disorder is rendered by a Gaussian (Czjzek) noise with an adjustable weight relative to Vzz. The number of free parameters is limited to three, as compared to a sole scale factor for the Czjzek model. Its characteristics are described as a function of the given asymmetry parameter and of the strength of the noise. The aim is to lead to a practical tool which may help to retrieve, as far as possible, the information about the local environment perturbed by disorder from hyperfine measurements and notably from NMR spectra of quadrupolar nuclei. As an example, that extension is applied to some static NMR spectra of 71Ga in covalent glasses. Calculated static 71Ga NMR lineshapes are shown as a function of the parameters of the extended model.

Published
2010
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