TABLE OF CONTENTS. Organizational chart of CEMES. Overview and remarkable results p 1-4

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2 TABLE OF CONTENTS Organizational chart of CEMES p i - iv Overview and remarkable results p 1-4 The results, by teams I. Crystalline Materials under Stress (Matériaux Cristallins sous contraintes, MC2) p 5-24 II. Nanomaterials (Nanomatériaux, nmat) p III. Nanosciences (Groupe NanoSciences, GNS) p IV. Support and Technical Services, Instrumentation p Bibliographic lists, by teams Articles in reviews MC2 p nmat p GNS p Chapters of Books, by teams p Invited International Conferences MC2 p nmat p GNS p 125 Annexes Annex 1. Teaching and Formation by Research, Information, Scientific and Technical Culture p Annex 2. Permanent Formation p Annex 3. Health and Safety p 137 Annex 4. Ethical Considerations p 139

3 Organigramme du CEMES janvier 2009 DIRECTION Jean-Pierre LAUNAY Assistante de direction Aurore Pruvost Bureau de direction J.-P. Launay, A. Claverie, A. Couret, C. Joachim Secrétariat général Michel Errecart GROUPES DE RECHERCHE POLES D APPUI A LA RECHERCHE CONSEILS COMMISSIONS Matériaux Cristallins sous Contrainte MC2 Alain Couret Marie-José Casanove Nanomatériaux nmat Alain Claverie Nanosciences GNS Christian Joachim Services communs Administration M. Errecart Bibliothèque I. Labau Informatique X Infrastructure M. Errecart Valorisation & Communication E. Philippot Support & développement techniques Electronique C. Pertel Mécanique L. Guiraud Préparations TEM J. Crestou Mesures et caractérisations Mesures Physiques Ph. Salles Microscopie électronique F. Houdellier Rayons X J. Jaud Spectroscopie Optique A. Zwick Conseil de Laboratoire Conseil Scientifique Conseil Scientifique et Technique Commission Locaux Commission Hygiène et Sécurité

4 CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CENTRE D'ELABORATION DE MATERIAUX ET D'ETUDES STRUCTURALES Personnel permanent du CEMES (ITA-IATOS-Chercheurs-Enseignants chercheurs) Octobre 2009 La liste complète du personnel est présente dans les tableaux excel 3.3 S2 et 3.5 S2 ** Services Communs ** Secrétariat Général : M. Errecart IE1 Assistante de Direction-Personnel : A. Pruvost TCE Accueil : -G. Fouillaron Gestion financière, missions : TCN - V. Antony AJTR (IATOS) - R.M. Mélendo TCN - M. Trupin AJTR - C.Vidal TCN Service Informatique: - O. Bancilhon AI - P. Bassoua AI (ITAOS) - J.N. Fillon AI Bibliothèque - I. Labau AJTR (50%) Infrastructure : bâtiments, campus : - D. Caulet TCE - P. Païva TCE - G. Combarieu TCN - A. Magdaléna TCN Communication Partenariat et Valorisation : - E. Philippot IR2 ** Support & développements techniques ** Service Electronique : - C. Pertel IR2 - L. Pettiti AI (IATOS) Service Mécanique : - L. Guiraud IR1 - O. Auriol TCN - A. Bouzid AI (ITAOS) - J.P. Boué TCE Service Préparations d'échantillons : - J. Crestou IE - C. Crestou TCN - D. Lamirault AJTR (IATOS) ** Mesures et caractérisations ** Mesures Physiques : - P. Salles AI Service Microscopise électronique : - F. Houdellier IR2 - C. Deshayes TCS (40%) - S. Joulié IE2 Service Spectroscopie optique : - A. Zwick IR1 - S. Moyano TCN (IATOS) - F. Neumayer AI (IATOS) Service Rayons X : - J. Jaud IRHC

5 ** Groupes de recherche ** MC2 nmat GNS Benoît Magali (CR) Caillard Daniel (DR) Casanove Marie-Josée(DR) Combe Nicolas (Mdc) Coujou Armand (P) Couret Alain (DR) Demangeot François (MdC) Dolle Mickaël (CR) Douin Joël (DR) Durand Lise (MdC) Galy Jean (DR) Gatel Christophe (MdC) Kihn Yolande (CR) Lecante Pierre (CR) Legros Marc (CR) Levade Colette (MdC) Mompiou Frédéric (CR) Monchoux Jean-Philippe (CR) Morillo Joseph (P) Pettinari-Sturmel Florence (MdC) Ponchet Anne (DR) Roucau Christian (DR) Rozier Patrick (MdC) Tang Hao (CR) Vanderschaeve Guy (P) Agez Gonzague (Mdc) Arbouet Arnaud (Mdc) Bacsa Wolfgang(P) Benassayag Gérard (DR) Bobo Jean-François (DR) Bonafos Caroline (CR) Brouca-Cabarrecq Chantal (Mdc) Calmels Lionel (Mdc) Carles Robert (P) Cherkashin Nikolaï (CR) Claverie Alain (DR) Dexpert Jeannette (CR) Groenen Jesse (Mdc) Hawkes Peter (DR) Hébras Xavier (Mdc) Hytch Martin (DR) Mauricot Robert (Mdc) Mitov Michel (CR) Mlayah Adnen (P) Monthioux Marc (DR) Paillard Vincent (P) Puech Pascal (Mdc) Schamm-Chardon Sylvie (CR) Sciau Philippe (CR) Serin Virginie (P) Snoeck Etienne (DR) Verelst Marc (P) Warot Fonrose Bénédicte (CR) Ajustron François (Mdc) Bonvoisin Jacques (CR) Bouju Xavier (CR) Coratger Roland (P) Dujardin Erik (CR) Gauthier Sébastien (DR) Girard Christian (DR) Gold Alfred (P) Gourdon André (DR) Guillermet Olivier (Mdc) Joachim Christian (DR) Launay Jean-Pierre (P) Martrou David (CR) Ondarçuhu Thierry (DR) Péchou Renaud (Mdc) Rapenne Gwénaël (Mdc) C. Deshayes TCS (10%)* C. Bourgerette AI* B. Cambus IE2* D. Chassaing IE2* (en disponibilité depuis 1/01/04) L. Noé AI* D. Neumeyer AI* C. Deshayes TCS (50%)* R. Laloo (IE2)* G. Seine (IE2)(IATOS)* C. Viala (AI)(IATOS)* * ITAs et IATOS dans les groupes de recherche


7 OVERVIEW AND REMARKABLE RESULTS Introduction : the CEMES organization Since 2006, the CEMES scientific research is clustered in three large groups gathering permanent researchers each: the Crystalline Materials under Stress (Matériaux Cristallins sous Contraintes, groupe MC2), Nanomaterials (groupe nmat), and Nanosciences (Groupe NanoSciences, GNS). Inside each group, there is a strong integration of projects with extensive discussions and exchanges. This is original in the French landscape, at variance with the frequently encountered scheme based on a larger number of teams of much smaller size. We strongly believe that our organization present many distinct advantages : real scientific animation, increased cross-fertilization favouring innovation, easier diffusion of information, mutualisation, in particular for equipment projects, in a word, increased coherence. This structure with a few large groups has been maintained after the integration by CEMES of the Laboratoire de Physique des Solides de Toulouse (LPST, 10 permanent researchers). Regarding the technical staff, we have recently performed in 2008 a regrouping of the different services in three poles : general services, (infrastructure, finances, human resources, computers-networks, partnership, communication), support and technical developments (preparations, instrumentation), measurements and characterization (Electron microscopy, X-Ray, optical and physical measurements). This evolution was motivated by the long term tendencies observed in the academic research practice: the diversification of techniques, the need of associating several to solve complex problems, the weakening of recurrent support and the rise of research on contract. As these factors could threaten the laboratory integrity (which is by the way a general problem in Europe), we have decided to strengthen our cohesion also in the technical domain. Remark : as a result of our specific organization, we have interpreted in our way the AERES instructions about the Report length. Due to the size of our teams, we cannot restrain to 5 pages per team, but rather approach 20 pages. Remarkable results in the last four years In the last four years, the CEMES laboratory has obtained a number of remarkable results, first in the field of research results, attested by publications in scientific literature, and also in the field of sustained industrial relationships. Regarding research results, the detailed achievements are presented in the report, but we mention here only a few of them, which were published in highly ranked scientific journals (Nature, Science, Nature Materials, Nature Nanotechnology) and have been the subject of nine press releases from July 2005 to February 2009, as listed in Annex 1. Concerning electron microscopy, we have developed new techniques aimed at mapping fields at the nanoscale, notably strain, using holography (Nature, 2008) and observed giant diffusivity along dislocation cores in certain metallic alloys (Science, 2008). Five-fold twinning induced strain in nanoparticles has been elucidated (Nature Materials, 2008). We have improved the reflectance limit of cholesteric systems, exploring a possible application to smart windows (Nature Materials 2006). Double-walled silica nanotubes obtained by a unique bio-inspired mineralization of a selfassembled peptide scaffold have been reported and open a new strategy for building dielectric nanooptical structures (Nature Materials 2007). Individual carbon nanotubes have been successfully addressed to yield a nano-squid device (Nature Nanotechnology, 2006, Cover illustration). Finally several examples of moleculemachines or molecular machineries have been demonstrated : trapping and moving metal atoms with a 6-leg molecule (Nature Materials, 2005), a rack-and-pinion molecular device (Nature Materials, 2007), the rolling of a single molecular wheel (Nature Nanotechnology, 2007, Cover illustration), the step-by-step rotation of a single molecule-gear (Nature Materials, 2009). The decay rate of the electronic conductance of a long molecular wire as a function of its length has been exactly measured on a single and well identify oligomer (Science, 2009). 1

8 Another important aspect is the intensity and quality of our industrial relationships. Indeed, since many years, we have sustained relations with Semiconductor and equipment supplier companies (STMicroelectronics, Soitec, NXP, Mattson ) in the field of materials and process optimization for Ultimate Silicon technology. CEMES has unique equipment and know-how in the fields of ultra-lowenergy ion implantation, doping optimization, layer transfer, stress building and the fabrication of nanocrystal flash memories. Our industrial relations in this area are permanent and systematic. Thus, since 2005, we have been 8 times partners with STMicroelectronics within European or ANR projects, and we shared 5 BDI (Doc grants). We were members of Alliance Crolles II (STM/NXP/Freescale) and now are part of the new Alliance (STM/IBM/LETI), with support from Minefi (Ministry of Economy, Industry, Employment), in the frame of the implementation of the 32/22 nm CMOS processes (Nano2012). We are also partners with Soitec (3 ANR projects, 3 recurrent groundwork research contracts, 2 CIFRE doc grants), in which A. Claverie is scientific consultant since Laboratory evolution in the regional, national and international environment The CEMES laboratory is well integrated in its environment, the term environment covering different levels. In the regional environment, the laboratory plays a role in the structuration of Physics in the Toulouse area. Thus we have recently incorporated (admistratively in 2007, effectively in 2008) the LPST. CEMES now gathers on a single site most of the scientists connected to Condensed Matter Physics. This was announced as one of the scientific objectives of the last quadriennal period, and we consider that this integration is a success as it can be judged in the scientific report. (Incidentally, this operation has been realised entirely on CEMES financial means). In the same spirit, we incorporate now scientifically and administratively the team of J.-F. Bobo at ONERA, which keeps its own facilities and premises on the ONERA site. Of course, the Laboratory is present in local networks such as Pôle de compétitivité Aerospace Valley. The Laboratory has participated to the scientific definition and is belonging to the Toulouse integration center of the NanoInnov initiative (A large national program on Nanotechnologies gathering three sites, Grenoble, Paris-South and Toulouse), although at the time of writing (Aug 09), no clear picture of the solid actions and financing has emerged for the Toulouse site. Actually, the next expansion of the Laboratory relies on the CPER operation Campus Gaston Dupouy. This operation, which expands over the period, is entirely financed, and the main milestones have been carefully planned. The general objectives are i) the development of Nanosciences at the atomic level, and ii), the final setup and upgrading of the optical equipment originally coming from the former LPST Laboratory. More details can be found on our Web site at the following address The CPER operation amounts to 4.33 M (TTC) for equipment and 4.38 M (TTC) for the Eco-Lab building renovation which will become the Pico-Lab of CEMES, the funding coming from the CNRS, the FEDER, the Midi-Pyrénées Region and the community of Toulouse agglomeration. The operation is planned in three steps : (i) a first sequence of equipment acquisition with installation in the existing premises, (ii) The complete Eco-Lab building renovation with dedicated facilities such as clean rooms and vibration-free supports for special atomic-precision equipments, and (iii) a second sequence of equipment acquisition, with in particular a four-probe LT-UHV STM system connected to an atom-manipulating LT-UHV-STM. At the time of writing, step (i) has been achieved, step (ii) is in progress with the elaboration of the detailed description of the new building with the main contractor ( maitre d oeuvre ), the real works being planned for the period, step (iii) is in preparation for achievement in , and will be accompanied by a reorganisation of the remaining CEMES installations. We manage good relations with nearby Universities and Engineering schools : Université Paul Sabatier and INSA (to which we are linked by specific conventions), and also Ecole Supérieure d Aéronautique et de l Espace (SupAero, now part of ISAE). In the case of INSA, we have a strong and fruitful connection with Laboratoire de Physique et Chimie des Nano-objets (LPCNO) which follows similar objectives as us, but with a complementary expertise and equipment. As far as Université Paul Sabatier (UPS) is concerned, several CEMES Faculty members have special responsibilities (V. Serin : coordinator of the Physics search committee, A. Coujou : vice-director of the Ecole Doctorale, J.-P. Launay : coordinator of the Matter Science Pôle at UPS). In the recent years, UPS has increased its interest and support to research, by launching specific programs with competitive applications. In this frame, CEMES has been successful through its NANOMOPI proposition in 2007 (NANOMOPI = Nanosciences, Molecules, Picotechnologies) and NANOMOL in 2009 (see in the Project section for this last one). Thanks to the NANOMOPI attribution of a PhD 2

9 and a post doc grant, we obtained major results in the field of carbon nanotubes (their individual connexion to electrodes, their magnetoresistance, electrical and Raman measurements), and also in molecular assembling and paving by molecules on surfaces. In the national and international environment, the CEMES laboratory plays also a recognized role, either on the form of genuine scientific cooperations, or on the form of coordination actions. In the French domain, CEMES coordinates the METSA network (METSA = Transmission Electron Microscopy and Atomic Probe) of 6 sites. Regarding Europe, CEMES participates to several IP projects (NanoCMOS, PullNano, FOREMOST, NAPA,) a few STREPS (REALISE, NanoMan, ATOMICS), several networks (ESTEEM, Plasmo-nano devices, Women In Nano, Frontiers) and has been coordinator of one IP (Pico- Inside), a STREP (CHIC, on Quantum Computing) as well as a project of the Volkswagen Foundation. We obtained one of the few Young Researchers projects of the ERC (Project COMOSYEL leaded by Erik Dujardin). In addition, we have been asked to coordinate the Atom technology part of the Nano- ICT (ICT = Information and Communication Technologies) action (CA), of the ICT FET (FET = Future and Emerging Technologies) EU program. This is a unique opportunity to be at the source of the next call in the field of Atom Technology & mono-molecular electronics. Beyond Europe, CEMES is one of the five satellite institutes of the MEXT Japanese project MANA ( with a 10- years and 150 M$ program dedicated to innovative nanosystems and materials. Since April 2005, C. Joachim is managing the A*STAR VIP Atom Techn. research program in Singapore under an official contract with the Singapore government through its science agency A*STAR. At IMRE, a group of 12 researchers (5 permanents, 5 post-doc and 2 Doc) is developing single molecule (or surface atomic circuit) logic gates and mechanical machineries, the corresponding surface atomic wire multiple access interconnections and the associated packaging technology at the surface of a semi-conductor surface. This is developed in parallel and full coordination with the CEMES micro-clean room (DUF) atomic scale interconnection machine dedicated to insulating surfaces. Finally an important point in which the CEMES members are particularly active is the organisation of international conferences. The complete list is too long to be given here, but we can quote the Carbon 09 conference in Biarritz (chair : M. Monthioux, 600 participants), the EDGE 2009 conference in Banff, Canada (Co-chair V. Serin, 300 participants), the International Molecular Electronics Conference 2009 in Hawaii (Co-chair : C. Joachim, 45 participants). Several symposia have been organized on a regular basis in the frame of the Materials Research Society (USA) and its European counterpart E-MRS on Materials and Processes for Non Volatile Memories (chair : A. Claverie, 2007, C. Bonafos, 2009) and on Si Front End Processing (F. Cristiano, A. Claverie, four symposia since 2005). Each of these symposia usually gathers about attendees. The rise of valorisation and patent activity There has been a strong increase in research valorisation and patent activity. When comparing with the previous period, while the 2006 report mentioned 5 patents (not all initiated in CEMES), now we can quote 7 patents which have been deposited, plus 3 under elaboration. In addition, 4 patent extensions and 7 softwares have been submitted. In the last years, two start-ups have been created : Pylote (Société par Actions Simplifiées, SAS, created in 2008), devoted to the flashpyrolysis elaboration of nanoparticles, which is presently hosted in CEMES, and Circlight (SARL, created jan 2009), devoted to a new system for lighting UHV chambers from the port-holes. Thus in a general way, the patent culture is rising in the laboratory, and researchers consider more systematically the possibility to submit a patent or create a startup. Communication and participation to the public debate A final point is worth to be mentioned, the participation to scientific dissemination and even public debate. It corresponds to an important solicitation of our environment, and since many years, CEMES participates to popularization actions towards scholars and the general public (see Annex 1). Thus each two years, the laboratory participates in Science Festivals, with Opendoors manifestations. It culminated in 2005 in the context of the World Year of Physics, and CEMES had a leading role in the overall organization in Midi-Pyrénées, with the result that the affluence peaked to more than 500 scholars and 600 visitors. In addition, we participate to many Université des Lycéens actions by conferences in various Lycées on themes such as Nanosciences or modern materials. 3

10 In the last 4-years period, the solicitation to participate to radio and TV emissions has strongly increased, and several video reportages, with national diffusion, have been shot at CEMES (see Annex 1). There is clearly an increase in CEMES notoriety and visibility. These activities give us some ability to interact with a wide variety of interlocutors. And since the research themes of CEMES linked to nano are at the corner of several societal interrogations, it was important to communicate our vision on such complex problems. C. Joachim has written a book for the general public: Nanosciences. La révolution invisible ( Le Seuil, 2008) in which the nano realm is put in perspective. This book attracts a lot of attention and is already translated in Russian, Portuguese and English. We have participated to radio emissions, national and local debates, and even to a Senate hearing of Office Parlementaire d Evaluation des Choix Scientifiques et Technologiques (OPECST), see Annex 1. Distinctions and highly competitive success Several members of CEMES have been distinguished, or have succeeded in highly competitive personal applications : J.-P. Cleuziou obtained two Ph D prizes after his thesis in 2007 : the C nano prize, category fundamental and the innovation prize of the Academie des sciences, inscriptions et belles lettres de Toulouse. C. Joachim obtained for the second time the Feynman prize in Nanotechnology in M. Hytch obtained the FEI European Microscopy Award in 2008 J.-P. Launay was renewed as senior member of Institut Universitaire de France (IUF) from 2003 to 2007 Finally E. Dujardin obtained in 2008 one of the very few ERC young researcher grants in chemistry and physics (only 4 for CNRS). 4

11 I. CRYSTALLINE MATERIALS UNDER STRESS Numbers such as Mxy refer to the list of papers of the MC2 group in the Bibliographic list The «Matériaux Cristallins sous Contrainte» (Crystalline materials under stress) group works to uncover the underlying mechanisms involved in deformation and strain relaxation of materials submitted to external or internal stresses. The main problems to be addressed concern : the plastic deformation of materials undergoing thermal or mechanical applied stresses; the accommodation of internal stresses by epitaxially grown nanostructures or by host lattices submitted to chemical or electrochemical insertion / extraction of guest species; the size effects in nanoparticles. The related analyses focus on the role of crystalline defects and free surfaces, e.g. dislocations and interfaces in deformed materials and strained layers, surfaces in nanosized particles, and more generally on the interaction between stresses, elastic strains and all kinds of perturbation of the crystalline order. The aim of these studies is to provide a deeper understanding of the mechanical, optical, electronic or magnetic properties of the studied materials. To reach these objectives, we have developed a multiscale approach based on complementary experimental investigations coupled with modelling. Transmission electron microscopy (TEM) used in different modes (conventional, high resolution, EELS, convergent beam diffraction) and x-ray diffraction and scattering are currently used for characterisations at atomic and microscopic scales. A new part of our activity consists in exploring optical and vibrational properties of elastically strained nano-objects through micro-spectroscopy (Raman, Photoluminescence). Efforts are also devoted to develop new methods for measuring stress and strain from transmission electron microscopy in nanostructures. For the studies of plasticity and mechanical properties, we perform in situ straining experiments, a technique for which the CEMES is internationally recognized and is continuously developing new tools. We are also involved in new developments of x-ray diffraction techniques (WAXS : wide-angle x-ray scattering), UV optical spectroscopy and TEM (Cs-correction). Using these techniques, a wide range of materials is investigated, ranging from model materials built for research purpose to materials with complex microstructures designed for applications. The investigated materials are either developed in the group or processed by collaborating groups or industrial companies. In particular, the group benefits from its own expertise in solid state and soft chemistry routes for the synthesis of new chemical compounds. We also perform the epitaxial growth of oxide and magnetic metallic thin layers and nanodots thanks to the sputtering device available at the CEMES. Moreover, we are at the origin of the set-up of the first French Spark Plasma Sintering (SPS) machine in 2004 and of the creation of the SPS national platform (Plateforme Nationale de Frittage Flash PNF2 CNRS) in Toulouse. New routes for the elaboration of materials and device processing have been developed thanks to the astonishing performance of this technique and to the new potentialities it offers. Original materials with attractive properties for energy storage and aeronautic applications have thus been obtained. During the last few years, our potential in numerical modelling has been increased in such a way that simulation activities are now developed on our five scientific axes. The group makes use of different simulation techniques which are selected depending on the properties to be studied (electronic, optical, structural...) and the system sizes (from atomistic to macroscopic). First-principles methods (Density Functional Theory) are applied to different materials for which an accurate description of the electronic structure is essential. Semi-empirical interaction models are developed in order to investigate specific problems involving large number of atoms, using Molecular Dynamics or Monte Carlo simulation techniques. Mechanical and thermal properties at a mesoscopic scale are modelled by the Finite Element Method, with a multi-physics approach as required to simulate SPS processes. Twenty five permanent researchers (15 CNRS and 10 lecturers of Universities) belong presently to the MC2 group. During the last four years, the group has recruited three new scientists and has welcomed eight colleagues (three from the LPST-Toulouse, three from the ex-cmi group of the CEMES, one from the CINAM-Marseille and one from the N-mat group of CEMES). At the same time, four persons retired and one is presently working for the foreign office in Barcelona. Eleven PhD students (five of them being shared with a French or a foreign laboratory) and five post-docs are also working in the group. Our research is supported by around fifteen projects (ANR, Régions, ). The group is involved in the direction of 4 GDRs (Relax, Mecano, Nano-alliages and SPS) and has organised several scientific manifestations. We also would like to underline several shared projects with other colleagues of the CEMES and of many other laboratories in Toulouse (LCC, LPCNO, LPQ, CIRIMAT, ISAE, LAAS, EMAC). We are fully implicated in the host activities of the European ESTEEM and French METSA networks, both of them being dedicated to electron microscopy. The group activities are distributed into the five following principal axes: 5

12 1. Crystalline defects and plasticity mechanisms 2. Microstructure and mechanical properties of alloys for aeronautics 3. Design of materials: elaboration, process, device 4. Stress at the nanometric scale : impact on structural and physical properties 5. Size effect in nanometer-sized materials I. Crystalline defects and plasticity mechanisms Crystal plasticity is usually controlled by a limited number of elementary defect properties, even in complex structures. It is therefore of fundamental importance to have a detailed description of these mechanisms at the microscopic scale. Our activity is thus devoted to fundamental studies of the properties of crystalline defects, mostly in model materials, combining transmission electron microscope observations (mainly in situ), atomistic simulations and modelling. Three domains of major interest for the mechanical properties of materials have been investigated. The first deals with high-temperature mechanisms involving diffusion which, in spite of their obvious importance, are very poorly documented. The second one is a contribution to the domain of dislocation glide controlled by lattice friction. The third describes important advances in the understanding of interface properties, related to the very actual domain of small-grain materials and nano-layers. For the two last topics, ab initio calculations have been developed, in correlation with former in situ experiments. A book chapter on "dislocations and mechanical properties" has also been written in the book "Alloy Physics". A new model for the climb motion of dislocations Climb is a dislocation motion involving the diffusion of vacancies over large distances. Although it controls most of the high temperature mechanical properties of materials, it remains very poorly understood, especially as the only available models were derived in the 60's. Moreover, climb is difficult to study experimentally, because it is almost always combined with glide. Under such conditions, quasicrystals, which deform by pure climb only, are ideal model materials for climb studies. A new model of deformation by climb has been derived, based on microscopic observations [M211, M212]. It includes the nucleation of jog pairs on dislocations, and the formation of an osmotic force due to the under/over density of vacancies. It accounts for all "exotic" mechanical properties of quasicrystalline AlPdMn. Without any adjustable parameter, it is thus possible to explain i) the strong strain-hardening measured just after the yield, by the new equation θ os = kt/ωc(t) (Fig. I-1), where Ω is the atomic volume, and c(t) is the vacancy concentration at thermal equilibrium, ii) complex twosteps relaxations, and iii) values of the activation parameters different from those of the classical "Weertman type" models (abnormally high stress dependence of the climb velocity, activation energy higher than the self-diffusion one). This model can be transposed to the climb deformation of crystalline materials, i.e. superalloys at high temperature, and complex intermetallic alloys. It should be inserted in the near future in dislocation-dynamics calculations. Fig. I-1: Theoretical and experimental value of the strain-hardening coefficient resulting from the osmotic force, in quasicrystalline AlPdMn. In particular, the creep properties of TiAl alloys have been modelled, on the basis of the observations of mixed climb (i.e. climb in a plane not perpendicular to the Burgers vector) described in section II.2 (alloys for aeronautics). I.1 Diffusion and dislocation climb at high temperature Staff : D. Caillard, A. Couret, F. Mompiou [M33,M37, M64, M70, M79, M211, M212] Fig. I-2: Vanishing of a phason wall trailed by a dislocation, at 580 C (in situ experiment, g = [1/0,0/-1,0/0]. The wall has completely disappeared after 100mn. The exponential decay of the contrast intensity at 570 C is shown in (c) Kinetics of phason diffusion in quasicrystals Because of the lack of periodicity of quasicrystals, any dislocation motion leaves a fault named phason wall. Contrary to stacking faults in crystals, phason walls can vanish at high temperature, by the dispersion of their constituent phasons. The underlying mechanism is however not known. The speed of vanishing of the contrast of phason walls has been measured, as a function of the temperature, in AlPdMn (Fig. I-2). The corresponding activation energy is close to that of self-diffusion in crystals, which 6

13 indicates that, in addition to local changes in interatomic distances, phason motion involves the diffusion of various atomic species over large distances. Pipe-diffusion Apart from their role in the plasticity of crystals, dislocations can also convey atoms much faster than the perfect lattice. This so called "pipe diffusion" hypothesis, formulated in the 50's, was never evidenced directly before the set of in situ TEM experiments on Al(1%Si, 0,5%Cu) films carried out in Stuttgart and Toulouse. Small inclusions dissolve very fast into larger ones via the dislocations. First accidental, the experiment was redone and controlled to gain access to the main parameters of this basic phenomenon of solid-state physics. See highlight HL. 1 for more details. HL1 - In situ TEM observation of giant diffusion through dislocation cores M.Legros [M31, M207] The term "pipe-diffusion" first appeared in 1964 [1] and refers to the ability of dislocations to transport atoms, interstitials or vacancies much faster than the bulk crystalline lattice. Although considered as a basic "brick" of solid state physics, because it is involved in several materials science domains such as metallurgy and geology, the pipediffusion phenomenon has almost never been observed and thus directly quantified [2]. As for bulk diffusion, the pipe diffusivity D P varies exponentially with temperature:. Our first observation of the phenomenon was fortuitous since we were looking in situ inside a TEM at the behavior of dislocations in Al thin films containing 1%Si, mainly in nano-sized precipitates [3]. We realized that small Si precipitates connected to larger ones by a dislocation disappeared much faster than when isolated (see Figure). By following the volume change of the dissolving particle, we were able to measure the Si atoms flux through a single dislocation and derive its diffusivity. Repeated at different temperatures, the experiment showed that the activation energy of a "pipe diffusing" Si atom [4] is 20% lower than when diffusing through the perfect lattice. Our results show that, around 420 C, the diffusivity along a single dislocation is between 300 and 800 times faster than bulk. Fig. HL1 : In situ TEM observation of the fast dissolution of a Si nanoparticle A through a dislocation d 1 at 420 C. The phenomenon, known as pipe diffusion, has been fully characterized by measuring in real time the volume of the disappearing precipitate (red curve) [1] LOVE, G. R., Acta Metallurgica 12 (1964) [2] VOLIN, T. E., LIE, K. H., BALLUFFI, R. W., Acta Metallurgica 19 (1971) [3] LEGROS, M., KAOUACHE, B., GERGAUD, P., THOMAS, O., DEHM, G., BALK, T. J., ARZT, E., Phil. Mag. A 85 (2005) [4] LEGROS, M., DEHM, G., BALK, T. J., ARZT, E., Science 319 (2008) I.2 Dislocation glide and lattice friction Staff : M. Benoit, D. Caillard, M. Legros, C. Levade, J. Morillo, H. Tang, G. Vanderschaeve. Post-Doc : N. Tarrat (ANR SIMDIM ) PhD : D. Martineau (CIFRE-Freescale, 2009-), B. Khong (CIFRE-Freescale, ) [M 53, M171, M230, M262] Dissociation of dislocations in elemental semiconductors The analytical modelling of the motion of dissociated dislocations in semiconductors has shown that a large number of metastable configurations are expected, for which the dissociation distances are asymmetrically distributed with respect to the equilibrium value. This model has been subsequently validated by the reexamination of data from the literature of the dislocation dissociation width under high external stresses, in Si and Ge. One consequence is that, in contrast with earlier hypotheses proposed in the literature, the mobility of a Shockley partial depends only of its character and not of its position (leading or trailing). In addition, a rough estimate of the depth of the Peierls valleys has been given. Ab-initio calculations of dislocations in titanium The analysis of dislocation properties requires an accurate atomistic characterization of the dislocation core, which can be obtained by ab initio first principles methods like the density functional theory (DFT). Simultaneously, a good description of the long range associated strain field is needed, which in turns requires atomistic simulations on large cells with periodic or fixed boundary conditions, that are only possible using approximate interaction models. Since 2006, we have initiated atomistic simulations of screw dislocations in hcp α-ti in the framework of the ANR project «SIMDIM». This choice results from our sound understanding of the dislocation properties in α- Ti, obtained by earlier in situ experiments. Our study of the core structure of the <11-20> screw dislocation has shown that only approximated models taking explicitly 7

14 into account the covalent directional bonding of d electrons can properly account for the preferential prismatic core spreading against the basal one (Fig.I-3). I.3 Small-grained materials, thin layers, and interfaces Staff : D. Caillard, M. Legros, C. Levade, F. Mompiou, G. Vanderschaeve. PhD : D. Martineau (CIFRE-Freescale, 2009-), B. Khong (CIFRE-Freescale, ) [M132, M228, M229, M253, M255] In situ study of the Hall-Petch effect The Hall-Petch effect is at the origin of the high strength of nano-materials. It describes their increase of strength, as a function of the reduction of their grain size, and relies on the interaction between mobile dislocations and interfaces. This effect has been studied in both lamellar TiAl alloy, and aluminium containing a cell structure bounded by dislocation walls. The strengths of domains boundaries in TiAl against the motion of ordinary dislocations and twins have been compared to those of dislocations walls in Al, and the corresponding parameters involved in the Hall Petch law have been measured. The differences have been attributed to the different interface properties. Fig. I.3: Differential displacement maps for the screw component of a < > screw dislocations in α Ti, obtained with a) an EAM potential and b) DFT calculations, starting from the same initial position (black square). Black and white circles denote atoms belonging to different planes. Grain boundary mediated plasticity in metallic nanocrystals Grain boundaries (GB) occupy a high volume fraction in nanocrystalline (nc) and ultrafine grain (UFG) metals. In the past few years, international teams have focused on the role of GB in the plasticity of such nanostructured materials. However, since it was difficult to experimentally precise the mechanisms of plasticity in very small crystallites, mainly earlier works focused only on simulation. Combining micromechanical testing and post mortem TEM, we show that the sole motion of GB can carry plasticity, providing an alternate deformation mode to dislocation mechanisms. Indeed, these experiments clearly correlate grain size increase with an increasing plastic strain. In situ TEM straining experiments were also carried out to probe GB mechanisms both at pertinent timescale and length scale. In nc-al, we recorded the dynamic of GB motion, showing GB migration perpendicular to the interface under an applied stress. The very fast GB motion even at room temperature indicates that long range diffusion does not operate (Fig. I-4). In UFG Al, we show that GB migration is coupled with the applied stress, in a mechanism producing a small shear strain (see highlight HL. 2). These results could not be satisfactory explained with models accounting for GB motion, because either they were too restricted to peculiar GB or because they imply long range diffusion. The Shear MIgration Geometrical (SMIG) model that we propose is a generalized formulation of existing theories requiring a limited atomic shuffling. It seems suitable to explain GB mediated plasticity in ordinary polycrystals. Fig. I-4: TEM dark-field micrographs taken in nc-al deformed in-situ. Note the fast motion of the lower part of the grain-boundary. The dashed line indicates the grain-boundary position in a) Plastic relaxation of metallic thin films and interconnects Metallic interconnects are usually the first components to undergo plastic deformation in a microprocessor. This happens when thermal stresses arising from the difference between the coefficients of thermal expansion of the different materials (semiconductor, insulators, metal) exceed the yield stress of the metal. This yield stress was found to vary as one over the metal film thickness, but the reason for this dependence remains unclear. The most spread theory is based on the confinement of mobile dislocations that create in their wake interfacial dislocations near the film/substrate interface. However, this theory underestimates the yield stress of films deposited on amorphous interfaces. In collaboration with Austrian and German colleagues, we recently set up a method to strain metal films inside a TEM. These in situ experiments confirmed that interfacial dislocations are confined in the metal film in the case of pseudo epitaxial metal/substrate interface. However, these interfacial dislocations annihilate when an amorphous oxide layer is in contact with the metal film and no dislocations sources were found to compensate this loss. Overall, thermal cycling causes an exhaustion of dislocations in metal films over oxidized substrates. Without easy deformation vector, higher stresses and alternate mechanisms are needed to plastically deform these films. By observing the surface of an Al film after cycling in SEM, we found that many whiskers and hillocks have grown over grain boundaries while other grain boundaries are much more 8

15 grooved. Heavy diffusion at the surface and at grain boundaries may thus contribute significantly to the plastic deformation of metal films and act as a substitute for the exhausted dislocations. This fundamental finding needs to be better quantified to help understand how real devices are aging: a similar diffusion effect is observed in the metallization of real CMOS devices (Freescale Semiconductor) or in copper interconnects (STRESSNET network, ANR Crystal). Orientation relationships and martensitic transformations Interfaces are also important in shape memory alloys, which exhibit a martensitic transformation at decreasing temperature and/or increasing stress. In CuAlNi, the interfaces between the austenitic and martensitic phases are parallel to irrational planes, which could be predicted only by the phenomenological theory of martensitic transformation (invariant planes). An alternative method has been proposed, based on the continuity of the dense planes across the interface ("edge-to-edge matching"), obtained by the superposition of the reciprocal lattices of the two structures. It allows one to predict the nature of the interface, irrespective of the deformation induced by the phase transformation. HL2 - Grain boundary mediated plasticity: from experiments to modelling F. Mompiou, M. Legros, D. Caillard [M229, M253] Grain boundary (GB) migration has been considered recently as an alternative deformation mode to dislocation mechanisms in nanocrystalline and ultra-fine grain metals. However, because of the difficulty of exploring plasticity mechanisms in very small crystallites, this mechanism has never received a clear confirmation. To investigate this phenomenon, we have performed a series of dynamical observations in a TEM on fine grained Al polycrystals subjected to an applied stress. They show the fast migration of general high angle GB in response to the stress (see fig. a and b). A shear strain, smaller than expected by existing models relying on specific GB, has been measured thanks to markers trapped in the specimen and image correlation analysis. We propose a general model able to describe the shearmigration coupling for a given GB. The Shear MIgration Geometrical (SMIG) model consists in finding the multiple ways two adjacent lattices are related by a combination of a rotation and a shear. For a given GB plane, misorientation angle, and shear strain, the migration distance can then be calculated. An example of coupling is shown in figure c. This model, compatible with small values of the shear strain as experimentally observed, gives a suitable description of GB migration in polycrystals. Fig. HL2: In-situ stress assisted grain growth in an Al polycrystal. at 350 C. a) and b) are two micrographs of the same area taken at different time. Under a tensile stress (T), G1 grows (the dashed line corresponds to the former position of the GB) at the expense of adjacent grains. Note the presence of small precipitates labelled X which act as markers. c) Example of a coupling mode in the SMIG model: parallelograms 1 and 2 are related by the combination of a rotation (θ) transforming 1 in 1, and shear transforming 1 in 2. Knowing the GB plane (P), the migration distance can be deduced. Simulation of dislocations at GaN/GaAs(001) interfaces The GaN is an important wide gap material for optoelectronic applications in the UV-visible range. The stable wurtzite structure of bulk GaN is at the origin of spontaneous polarization at interfaces of multilayered structures which alters the performance of components. A way to overcome this main drawback is to grow metastable cubic GaN, which can be achieved by epitaxial deposition on GaAs(001) substrate. The huge misfit of 20% between these materials is accommodated by the formation of an edge dislocation array at the interface. The knowledge of atomic structure at this interface is important for understanding the stability of such layers and their electronic structures. This can be achieved only with the help of precise atomistic calculations by using density functional theory (DFT). In the framework of the ANR ''SIMDIM'' project, we have determined two most stable dislocation cores. The first one (''8 atoms core'' configuration) is stable under the nitrogen rich condition. By removing the most constrained N atoms columns, we have obtained a second configuration (''open core''), stable under the sub-stoichiometric nitrogen condition with lower energy (Fig. I-5). The corresponding electronic structures present negative 9

16 density (hole) distributions localized in between dislocation cores at the interface. of precipitates by hardening the γ phase and decreasing the interphase diffusivity. The existence of short-range order in the γ matrix, responsible for the collective motion of dislocations and formation of pile-ups, was also demonstrated. The individual behavior of dislocations resulting from confined plasticity has been simulated at a mesoscopic scale and compared to observations (Fig. II-1). Also, the Finite Elements models compare fairly well with the macroscopic mechanical properties of non-aged superalloys. Fig. I-5: Isodensity surface of charge density of the most stable dislocation core. II. Microstructures and mechanical properties of alloys for aeronautic Metallic alloys for applications in aeronautic have been an important research area in the MC2 group for the last twenty years. The development of high performance, reliable and light alloys requires the understanding of the micro and nano structures as well as the elementary mechanisms responsible for the macroscopic mechanical properties. Our studies at different scales are mainly supported by TEM analysis of the deformation micromechanisms. We use the classical technique of post mortem observations of macroscopically deformed samples. We also carry out in-situ deformation tests inside the TEM, a technique for which the group is internationally recognized. The group has participated to all the national projects on the improvement of the aeronautic alloys (R2IT, RNMP, ANR, FRAE, RTRA) in which numerous academic institutions are involved. Our work in collaboration with the main industrial companies in the field (Airbus/EADS, Aubert & Duval, Safran, Messier- Dowty, Mecachrome) confers to the group an expertise that can be used for the design and the optimization of alloys from fundamental considerations at the nanoscopic and microscopic levels. Recent developments include the four main categories of metallic alloys involved in aeronautic applications. II.1 Superalloys Staff: A. Coujou, J. Douin, L. Durand, F. Pettinari- Sturmel [M43, M66, M101, M106, M107, M133, M138] Nickel-based superalloys are two-phased materials with hardening γ precipitates (L1 2 structure) embedded in a short range ordered γ phase. These alloys are used in the warmest parts of the turboreactors. In extreme temperature, stress and environment conditions, nickelbased superalloys undergo profound morphological transformations that greatly influence their lifespan. The elementary mechanisms responsible for these evolutions are studied by combining nano and micro scale approaches. The emphasis was put on mechanisms at the origin of the rafting of γ precipitates during high temperature creep, and on the presence of heavy elements like rhenium which reduce the rafting Fig. II-1: Weak-beam micrograph and related dynamical simulation of a a/2[110] dislocation dissociated into two Shockley partial dislocations (L and T) trapped in a γ channel of a deformed MC2 superalloy. The γ precipitates are out of contrast and are delimited by the white lines. The width of the channel is approximately 40 nm. The shapes of the partial dislocations under the effective shear stress r τ with magnitude 450 MPa and at 20 from [110] are superimposed on the micrograph (black dashed lines). II.2 Titanium alloys Staff: A. Coujou, J. Douin, F. Pettinari-Sturmel PhD: P. Castany (MESR, ), N. Escalé (CIFRE-Aubert & Duval, 2008-) [M124, M179, M239] Titanium alloys are widely used for aeronautic applications because of their good mechanical properties combined with their low density. The multiphased α/β TA6V alloy is the most studied titanium alloy in aeronautic because of its low density combined with excellent mechanical properties. Its use is however limited by its relatively bad surface properties. Different surface treatments were elaborated to improve the surface properties. We have shown that the nano-crystallised layer formed at the surface is a barrier for the propagation of dislocations, while in the area where nitrogen has diffused, short-range order evolves to the formation of long-range ordered nanoprecipitates leading to a more localized deformation. The deformation micromechanisms of the TA6V bulk alloy have also been precisely investigated and it has been shown that the strength of the material is mainly due to the core structure of the screw dislocations (see highlight HL3) and that short range order has a non negligible effect in the deformation of the α phase. The 10

17 role of the different interfaces has also been clearly enlightened. II.3 Structural hardening Staff: A. Coujou, J. Douin, F. Pettinari-Sturmel Post-Doc : V. Vidal (ANR AMARAGE, 2007), B. Kedjar (ANR AMARAGE and ANR CONTRA_PRECI, ) The exceptionally good structural hardening of last generation aluminum alloys and steels find their origin in nanometric precipitation. To understand the macroscopic mechanical properties of these alloys, fine analyses were undergone, at a scale that requires High Resolution TEM imaging combined with geometrical phase analysis. Our study allows not only to determine the nature, size and volume fraction of the nanoprecipitates, but also the distance between them or their eventual orientation relationship with the matrix, as well as their strength and the stress field they generate in the matrix. HL3 - Direct measurement of the Peierls barrier energy J. Douin, P. Castany, A. Coujou, F. Pettinari-Sturmel [M124, M 179, M239 ] Fig. HL3. Weak-Beam TEM micrograph of r a dislocations extending in the (0001) basal plane of the hexagonal α phase of the TA6V alloy. At the junction between screw and non-screw segments (Fig.b), the dislocations take an angular shape with an angle ϕ i at the cusp. The relative variation in energy when stabilizing can be directly related through anisotropic computations to the escape angle ϕ (Fig.c). Amongst numerous types of obstacles, the stabilization of dislocations along preferential directions provides a major intrinsic contribution to the mechanical properties of numerous metals and alloys. We have developed a NEW general method based on TEM observations of the segmented shape of dislocations under stress for measuring the decrease in dislocations self-energy when they are locked in any specific orientations. Having a reliable experimental method to estimate this gain in energy has two major benefits: (i) it allows the strength of locking of such an obstacle to be quantified for the dislocation motion and (ii) it gives a constraint that simulations must fulfill in order to be representative of a crystal. The method is based on the measurement of the escape angle at the junction between a locked straight segment and anon-locked curved segment, the larger the gain in energy when stabilizing, the larger the angle at the cusp (fig.a). The relative variation in energy when stabilizing is then directly related to the escape angle ϕ measured in the glide plane by computing the modification of the shape of a dislocation loop assuming anisotropic elasticity (fig.b). The method has been applied to the hexagonal phase of an industrially important Ti-based alloy r where a significant in-core rearrangement of screw a dislocations reduces their energy by about 16% (fig.c). II.4 Intermetallic alloys Staff : A. Couret, M. Legros, J. Morillo, G. Molénat, J.P. Monchoux [M10, M12, M36, M56, M57, M61, M90, M92, M94, M109, M110, M228] Microstructures and mechanical properties of lamellar TiAl alloys In TiAl alloys, in consistency with the phase diagram, a lamellar microstructure can be formed with an appropriate chemical composition and a controlled thermal cycle. It is well known that an amount of lamellar areas enhances the mechanical properties of TiAl alloys, if the key microstructural parameters (phase and variant distributions, interface relationships, lamellae width, ) are finely tuned. That is true for the cast General Electric (GE) alloy selected for the first certified aero engine containing TiAl blades (GEnx). The present studies are thus devoted to the formation and plasticity of this lamellar microstructure and to the creep properties of a predominantly lamellar cast alloy. In parallel, we work on the development of TiAl alloys by Spark Plasma Sintering (Cf section III. 2). Our main results can be summarized as follows. During cooling, the formation of γ lamellae results from three different types of lamellar transformations, which are controlled by three competitive driving forces: local chemical composition variations, interfacial energy differences and short range elastic constraints. For the transformation occurring at high temperatures, the formation of precursor γ allotriomorph grains at grain boundaries has been evidenced. In particular, they play a determining role on the selection of the orientation variants. Over large zones (Fig. II-2), the deformation of this lamellar microstructure is controlled by a pilot orientation (among the six available) which imposes a 11

18 deformation mode to the other orientations through the transfer of dislocation across interfaces. From in situ straining experiments, the propagation of deformation across α 2 lamellae is explained in terms of an elastically-mediated transfer. Regarding the creep properties, the primary stage corresponds to the strengthening of soft zones and the creep resistance is controlled by the mean free path (lamellar width) of dislocations moving by a mixed climb, a new mechanism which has been investigated in details. Fig. II-2 : TEM image of a lamellar TiAl alloy deformed at room temperature. For each lamella, the phase, the orientation and the activated deformation mechanisms were determined. It can be seen that lamellae with orientation O1 and O2 deform by dislocations and twins, respectively. No dislocations were found in α 2 lamellae. Defects in Fe-Al Boron and Carbon are used in the Fe-Al intermetallic alloy as additive elements in order to improve their mechanical properties. Using an ab initio DFT approach we have studied some of their properties (complex defects for B in B2 FeAl and the phase diagram of the Fe-Al-C alloy around the κ-fe 3 AlC phase). In particular we have shown that, surprisingly, B atoms prefer substutitional sites on the Al sublattice (B Al ) and that there is a strong tendency of Fe vacancies (V Fe ) to form complexes with B Al. The strength of this effect seems sufficient to induce structural complexes in Al-rich alloys like Fe divacancies and V Fe -B Al complexes. III. Design of materials: elaboration, process, device The aim of this thematic is to design and process materials and devices to control the whole chain of the development of a material, going from the synthesis of new phases and microstructures to the processing of devices. For this purpose, our research focuses on two orientations, the first consisting in the chemical control of atomic arrangement, the second oriented on the mastering of the elaboration processes. The former topic is developed on the basis of an extended knowledge in solid state chemistry including several chemical routes (controlled atmosphere, hydrothermal synthesis, soft chemistry) and a panel of techniques to investigate many kinds of atomic arrangements (from amorphous to crystalline states), and sample shapes (single crystals, powders and thin films). The latter topic was initiated by the rapid development of the spark plasma sintering (SPS) technique throughout the world. The performances of this technique being promising, the CEMES set-up in 2004 the first French SPS machine, in order to give further impetus to elaboration studies. Thanks to the astonishing rapidity of the SPS process for many materials, we have proved the potentialities of this technique on ceramics (Al 2 O 3, Cr 2 O 3, SiC, ZrC ) and metallic alloys (TiAl). The control of the parameters of the process has been deduced from finite element simulations. We have studied the reactivity mechanisms during SPS synthesis, from material assembly, where reaction has to be minimized, to reactive sintering, where reactivity rapidity is a key point. This technique brought then together solid-state chemists and metallurgists around this new facility. III.1. Crystal-chemistry as a transverse tool for basic and applied research Staff : M. Benoit, M. Dollé, J. Galy, P. Lecante, P. Rozier, J.C. Trombe PhD : E. Dumont-Bott (CEA, 2008-), G. Jouan (MESR, 2008-), M. Grisolia (Universidad de Los Andes,Merida, Venezuela, 2008-). [M2, M3, M4, M5, M9, M19, M21, M39, M42, M45, M47, M48, M51, M52, M54, M60, M69, M71, M73, M74, M76, M98, M104, M113, M116, M117, M121, M137, M141, M156, M157, M170, M172, M176, M177, M191, M198, M216, M218, M219, M226, M240, M242, M259] Usually solid state chemists proceed via a test and trial process to find new compounds expecting new properties. Our approach is, in addition to the conventional structure/properties relation-ship study, to use the wide structural data base to select known compounds, determine structure/structure relation-ships and define chemical mechanism to develop a predictive approach. This approach allows us to design and synthesize new compounds with atomic lattice optimized to answer both basic and applied bottlenecks in domains ranging, as illustrated below, from solid state physic to electrochemical power sources. Magnetic properties Highly frustrated magnetism corresponds to specific arrangement of s =1/2, 3/2 elements inducing a perturbation in the spin ordering which drives to behaviours far from conventional ones. Only few compounds exhibiting such behaviour, its 12

19 understanding is mainly based on a theoretical approach. To validate these theories, there is a need for experimental data collected on compounds with atomic arrangements designed to be representative of different spin lattices. To answer this requirement, in the frame of an European Science Foundation Program, we developed hybrid chemistry using organic entities to isolate and arrange MX building units (M = Cu, V, Cr ; X= O, Cl). Using a trial and error process we are progressively able to define chemical parameters mastering the atomic arrangement as well as to find ways to grow single crystals large enough to perform magnetic characterisation. New compounds with selected spin lattice geometry (Kagome-type; triangular; square) have been prepared and the nearestneighbour spin-spin correlations coupling values controlled by the nature of organic entities. The experimental determination of each of the different contributions led then to consolidate and refine the theoretical understanding of highly frustrated magnets. Ionic diffusion and reactivity in solids One of the main restraints of the development of new systems for energy storage such as lithium based batteries and Solid Oxides Fuel Cells resides in the low ionic conductivity of solids. Its improvement implies to be able to favour and enhance the long-range diffusion of ions, i.e. to govern both the nature of their crystallographic site and the way they are linked (diffusion pathway). To achieve these goals, our approach consists to investigate, using neutron or X- Ray diffraction, the structure of compounds selected to be representative of different atomic arrangements and to identify the inert part (host network) as well as the mobile ions (guest species). Fourier analyses are used to determine the electron density maps around guest species. These maps, representative of ions delocalisation, can be considered as the track of ions diffusion pathways. The physical (ionic conductivity) and/or chemical (reactivity) properties of the compounds are determined using impedance spectroscopy and electrochemical tests. The different results are analysed with the aim to define structure / properties relationships and more specifically to determine the structural parameters which govern the efficiency of the processes. In the domain of anionic conductivity we studied model systems such as mbi 2 O 3 -MoO 3 based columnar and lamellar phases. The structures in Bi 2(n+2) Mo n O 6(n+1) series (n=3,4,5,6) were determined ab initio and related to each other via a periodic crystallographic shear mechanism. Observed for the first time to occur in [Bi 2 O 2 ] n layer, its extrapolation for n= explains the formation of the Aurivillius phase Bi 2 MoO 6. The addition of PbO allowed us to stabilise a columnar type structure for the composition Pb[Bi 12 O 14 ](MoO 4 ) 5. Structural study evidenced that in this compound, the anionic conductivity is due to O 2- exchange between MoO 4 tetrahedra, however limited by the presence of Pb 2+ cations acting as blocking point. Crystal-chemistry concepts have been applied to substitute Ln 3+ ions to Pb 2+. The charge compensation generates vacancies corresponding to the removal of some of the blocking points. It results in an increase of the diffusion pathway interconnection, leading to an increase of the anionic conductivity that can be enhanced by the direct control of the Ln 3+ size. For cationic diffusion processes, we have investigated the relationship between ionic mobility and chemical reactivity. Previous works on Ag or Cu vanadium based oxides allowed us to define new classes of materials that can be used as positive electrode in Li based batteries. In addition to the conventional insertion mechanism these compounds present a specific displacement phenomenon. This phenomenon is observed during the discharge of a lithium battery and corresponds to the reduction to the metal state and extrusion out of the structure of mobile specie. In the last four years, we have focused our activity on the understanding of the origin, efficiency and reversibility of such a displacement process. Structural investigation of selected compounds in (Ag or Cu) V O systems showed the V-O sub-network to correspond to the inert part while the Ag or Cu ions are the mobile and reactive species. The key parameter governing the efficiency of Cu or Ag displacement was found to be related to the host network flexibility. 2D layered host network appeared to be the most convenient. The layer flexibility was found to be dependent on the connection mode between the oxygenated polyhedra. Corner sharing, acting as oxygenated pivot, enhances the flexibility compared to edge or face sharing which increases the rigidity and prevents the displacement process. Lately, we investigated mixed (Ag and Cu) V O based compounds. The simultaneous presence of Ag and Cu ions leads to a competitive effect. We evidenced the ability of Ag ions to act as structure pillar inducing a perturbation of Cu ion localisation (Fig. III- 1). Electrochemical tests completed by in situ XRD studies confirm the Cu ions to be reactive. Once all Cu ions are fully reduced and extruded, the Ag behaviour change from inert to mobile and the Ag displacement is observed. These studies are currently extended to other transition metals (Nb, Mo) and anions (S, F) host networks with, in addition, the aim to control the electrochemical redox potential i.e. the battery voltage. Study of non-crystalline samples Glasses present interesting properties for different domains such as ionic conductivity, waste confinement or as substrate for electronic devices. However their structure being more complex than that of crystalline samples, they require specific experimental techniques such as Wide Angle X-ray Scattering, often coupled to numerical simulations. The data analysis is usually made using analogous crystals as starting building units of the atomic arrangement and gives clues to interpret physical properties. 13

20 In hydrous silica, we have shown that native defects such as Si-O dangling bonds can play a significant role as precursors in the laser-induced defect formation process. III.2. Processing materials and devices by SPS Staff : A. Couret, M. Dollé, L. Durand, J. Galy, G. Molénat, J.P. Monchoux, P. Rozier PhD : F. Guillard (CEA-, ), H. Jabbar (BDI Rég, ), G. Jouan (MESR, 2008-), A. Réhaut (CEA ) Post-Doc : G. Delaizir (ANR StockE, ) [M134, M145, M147, M158, M183, M199, M200, M227, M243] Fig. III-1 : Ag 1/2 Cu 1/2 V 2 O 5 structure and experimentally determined electron density maps showing the delocalisation (mobility) of Cu + ions and the role of Ag + ions as pillars. We have studied glasses in M 2 O Te2 Te 2 V 2 O 9 systems (M=Li, Ag, Na) which exhibit a electronic to ionic with increasing M 2 O amount. The results indicate that the increase of M 2 O amount disturbs the V-O chains leading to a loss of extended connection preventing the long range hopping electron mechanism. Numerical methods were also developed to obtain a better understanding of the structural, dynamical and electronic properties of silicate glasses. Molecular dynamics and DFT simulations performed on calcium aluminosilicate and hydrous silicate liquids and glasses, lead to a better knowledge of the local environment of the cations and to a possible interpretation of the experimental 17 O NMR spectra of a calcium aluminosilicate glass (Fig. III.2). Understanding and control of the SPS process Since the setting-up of the Spark Plasma Sintering CNRS platform (PNF2) in Toulouse in 2004, which remained unique in France till 2007, experimentalists and theorists have been interacting to get a better understanding of the SPS process. The SPS offers many advantages (ex. rapid sintering, sintering with no additives,...) with respect to conventional processes. The mechanisms occurring during SPS sintering are still controversial, and studies on different families of materials have been performed to understand the impact of SPS parameters, in particular current, voltage and pressure. A finite element method approach was also developed to simulate the spatial distributions of temperature, current and tension, as a function of physical parameters like electrical conductivity, thermal conductivity or specific heat of the die and of the sample and as a function of their geometry (Fig. III.3). The method has been validated by comparing the simulations with experimental temperature measurements on different materials (metal, semiconductor and insulator). This enabled us to design dies and to control the SPS parameters for the preparation of samples going from simple pellets to ready-made objects (Fig. III.4). Fig. III-2: Comparison between a) the experimental QMAS 17O NMR spectrum obtained on a calcium aluminosilicate glass by Stebbins and Xu, Nature 390, 60 (1997) and b) a simulated spectrum calculated on a glass of close composition using DFT. NBO and O3 refers to the non-bridging oxygens and to the oxygen triclusters, respectively. Fig. III-3: FEM simulations of the temperature field in the sample-punches-die assembly. From these simulations, the fields of temperature, current and tension can be established. Microstructure development in metallic alloys by SPS The aim of the present work is to investigate the capability of SPS process to sinter intermetallic TiAl alloys for turbine blade applications. This requires obtaining fully compacted samples exhibiting 14

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