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Les verres usuels, dits « silicatés », sont des matériaux irremplaçables car transparents, rigides et de faible cout. Mais ils ont un talon d’Achille : leur résistance mécanique, à tel point qu’ils sont l’archétype même du matériau fragile, qui reste élastique jusqu’à rupture. Cependant, à la fin des années 1940, on a observé avec étonnement que leur indentation à l’échelle du micromètre laisse une empreinte, trace incontestable d’une déformation plastique ! Réconcilier cette plasticité à l’échelle locale avec l’idée de rupture fragile reste une question ouverte, tant la description de l’écoulement plastique dans les amorphes est complexe. La conjonction de nouvelles techniques expérimentales et numériques a permis des progrès que nous décrivons ici.

International audience; In this study, lead metasilicate glasses (PbSiO3) were densified at different maximum pressures in a diamond anvil cell (DAC) at room temperature. The densified glass samples were investigated ex-situ by Raman spectroscopy to probe their pressure-induced plastic deformation limit and permanent structural modifications on the Q(n) distribution. With a high Pb content, this glass exhibits a low elastic limit at similar to 4 GPa, which is linked to an initial compact structure. Spectral curve fitting of the high-frequency region of the Raman spectra, consisting of symmetric Si-O stretching modes, exhibit subtle Q(n) population modifications with maximum pressure. This reveals silica network depolymerization where the proportion of non-bridging oxygens (NBO) increases at the expense of bridging oxygens (BO). Possible densification mechanisms are discussed in contrast to those known in other silicate glasses.

Environmental and aquaculture monitoring in seawater use standalone and robust underwater sensor networks to properly and regularly harvest useful data. The need of submarine images transmissions in real time require higher data rate. In this paper we introduce an innovative prototype of reliable magneto-induction based wireless submarine communication system adapted to a medium-range underwater telemetry application matching those requirements.

Costal pollution and seawater quality monitoring requires underwater sensors to be properly and regularly measured. This paper introduces an innovative prototype of reliable electromagnetic based wireless submarine communication system adapted to a medium-range telemetry application. This work, starting from the study of seawater properties describes the design and simulation results of antennas, matching circuits and modulation techniques to optimize the link budget and data rate between a surface buoy and underwater probes.

We demonstrate that symmetry breaking opens a new degree of freedom to tailor energy-momentum dispersion in photonic crystals. Using a general theoretical framework in two illustrative practical structures, we show that breaking symmetry enables an on-demand tuning of the local density of states of the same photonic band from zero (Dirac cone dispersion) to infinity (flatband dispersion), as well as any constant density over an adjustable spectral range. As a proof of concept, we demonstrate experimentally the transformation of the very same photonic band from a conventional quadratic shape to a Dirac dispersion, a flatband dispersion, and a multivalley one. This transition is achieved by finely tuning the vertical symmetry breaking of the photonic structures. Our results provide an unprecedented degree of freedom for optical dispersion engineering in planar integrated photonic devices.

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Phosphors based on rare earth ions are used to convert photons to useful wavelengths for a wide range of applications, but the improvement of their emission efficiency remains a key challenge in thin films. In this paper, we demonstrate theoretically and experimentally that a photonic crystal (PC) structure can efficiently enhance the luminescence properties of a down-shifting layer (DSL). Our new metastructure combines a DSL (Y2O3:Eu3+) and a two-dimensional (2D) planar PC (SiNx), the latter being specifically engineered to control simultaneously the absorption in the DSL and the emission into free space. A global emission enhancement of 77 times is obtained due to PC Bloch mode resonances. Additionally, this metastructure exhibits high transmission above 450 nm and favors the emission of converted light at specific angles, with an enhancement factor of up to 690. We explain how the slow and fast Bloch modes of the PC structure induce these giant absorption and extraction enhancements of light.

The seminal work of R.B. Wood (1902), who discovered anomalies in the reflection spectra of sub-wavelength metallic gratings, triggered the field of plasmonics, where ultra-thin metallic sheets laterally structured on a sub-wavelength scale, so called metallic meta-surface, are under operation. The goal of the field has extended considerably in the last decades and has aimed at arbitrary control over the amplitude, phase and polarization… of light waves at the sub-wavelength scale. All-dielectric meta-surfaces consisting in nano-structured thin films of high index dielectric material, are attracting much attention, owing to their capability to achieve the same goal as their metallic counterpart, yet with an enhanced efficiency (especially for the manipulation of strong optical resonances), being freed from significant energy dissipation as encountered in metallic nano-structures. All dielectric meta-surfaces have been around for quite a while, but were named differently (photonic crystal dielectric membranes or high index contrast gratings). Unless rare exceptions, the literature reports on structures with non-broken vertical symmetry. In the present contribution we emphasize that breaking the vertical symmetry of all-dielectric meta-surfaces provides a widely enhanced degree of freedom for the control of spatial routes and spectral characteristics of light, which depends, to an essential extent, on the local density of photonic states in the thin nano-structured dielectric film. As an enlightening illustration, we concentrate on a dielectric meta-surface formed by two super-imposed identical evanescently coupled gratings, with adjustable gap distance and lateral alignment. We show that this remarkably simple meta-surface can provide any local density of photonic states from zero (Dirac cone) to infinity (ultra-flat zero curvature dispersion characteristics), as well as any constant density over an adjustable spectral range. Exemplifying applications will illustrate the great potential of this new approach.

Underwater environmental sensor networks require wireless communications that can be obtained using electromagnetic waves. Thus, antenna design is a key factor regarding the global performance of such underwater transmission systems. The study of seawater properties leads to comparing the conduction loss and dielectric loss of an electromagnetic wave. A simulation model of an original antenna design is proposed to optimize link budget in underwater communication systems.

A l’heure ou un assistant vocal, un refrigerateur ou un smartphone peuvent debiter notre compte bancaire, ou une montre connectee peut mesurer et communiquer les parametres vitaux de son proprietaire a des services d’urgence ou prendre rendez-vous avec un medecin, ou un scanner commence a proposer un diagnostic, la revolution numerique bouleverse et interroge nos modeles de societe, leurs economies ou modes de gouvernance tout autant que nos rapports sociaux. Sante, education, commerce, transports, finances, medias, administrations, politiques, agriculture, relations, habitat, la digitalisation n’epargne aucun domaine. Des intelligences artificielles alimentees par des quantites ahurissantes de donnees emanant de millions d’objets connectes mesurent, analysent et influencent nos choix, comportements ou agissements.Les implications innombrables de ces technologies dans la vie quotidienne croissent a une vitesse vertigineuse. Elles necessitent de notre part une adaptation tout aussi rapide et pour laquelle nous ne sommes que partiellement prepares. L’egalite d’acces aux soins, a l’education et aux services publics est-elle menacee ? Quelles sont les consequences sociales de ce tsunami digital ? Pour repondre a cette question, il est d’une importance capitale de comprendre les mecanismes, actions et tendances de cette transition. L’utilisation d’une approche nouvelle, globale et systemique peut permettre de se l’approprier puis de se positionner individuellement et collectivement face aux enjeux et a la multitude de choix qui l’accompagnent. C’est le propos de cet article.

article i nfo Article history: Received 13 July 2012 Available online xxxx Low frequency vibrations, a universal feature of amorphous solids which is responsible for thermodynamical anomalies at low temperature, are complicated to record in high pressure device, notably because of the close- ness of the elastic line. We first present an experimental protocol allowing to record the in situ low-frequency Raman scattering of samples under high pressure in the diamond anvil cell apparatus with a high quality. This protocol is particularly adapted to study the evolution of the boson peak of glassy materials. The second part is dedicated to the study of the boson peak of a-GeO2, a typical strong glass. The results, which clearly show the non-Debye behaviour of this material at the beginning of the compression where an anomalous compression takes place, are compared to previous measurements on a-SiO2. Interpretation in terms of local structural transitions and discussions about the elastic nanoheterogeneities of the amorphous state are addressed.

We studied the low-frequency Raman and X-ray scattering behavior of amorphous silicon (a-Si) at high pressure throughout the range where the density-driven polyamorphic transformation between the low-density amorphous (LDA) semiconductor and a novel metallic high-density amorphous (HDA) polyamorph occurs. The experimental data were analyzed with the aid of molecular dynamics (MD) simulations using the Stillinger-Weber potential. The heat capacity of a-Si obtained from the low pressure Raman data exhibits non Debye-like behavior, but the effect is small, and our data support the conclusion that no boson peak is present. The high-pressure Raman data show the presence of a distinct low frequency band for the HDA polyamorph in agreement with ab initio MD simulations. Spatially resolved synchrotron X-ray diffraction was used to study the high pressure behavior of the a-Si sample throughout the LDA-HDA transition range without interference by crystallization events. The X-ray data were analyzed using an iterative refinement strategy to extract real-space structural information. The appearance of the first diffraction peak (FDP) in the scattering function S(Q) is discussed in terms of the void structure determined from Voronoi analysis of the MD simulation data.

In this study, we report the results of an in situ X-ray absorption spectroscopy investigation of the La2O3–B2O3–GeO2 (LBG) glass compressed in a diamond anvil cell until 17 GPa at ambient temperature. A pressure-induced coordination change of germanium from fourfold to sixfold is shown here. The analysis of Ge K-edge X-ray absorption near-edge structure spectra supports a model of mixing of fourfold and sixfold coordinated Ge sites during the compression/decompression cycle. This transformation proves to be irreversible: about 25% of sixfold coordinated Ge still exists at ambient pressure. This phenomenon underlines a polymorphism property of the LBG glass, whose origin lies in the complexity of composition.

We study the changes in the Raman optical vibrations of pure silica glass under high-pressure up to 4.3 GPa and room temperature, namely in the elastic domain. Several mechanical anomalies, as the decrease of bulk modulus between 0 and 2 GPa, have been revealed many years ago (P.W. Bridgmann, Am. J. Sci 10 (1925) 359), but no physical experiments have explained what happens at the atomic scale. Our experiments show that gradual structural reversible rearrangement from 0 to 2 GPa leads to a more flexible material, in good agreement with molecular dynamics (MD) simulations (L. Huang, J. Kieffer, Phys. Rev. B 69 (2004) 224203). Above 2 GPa, a fast homogenization occurs.

Normal silica glass is usually referred to as low density amorphous silica as it can be converted to high density amorphous silica by a hydrostatic pressure (polyamorphic transition). In this work in situ Raman experiments are performed in a diamond anvil cell up to 18 GPa. The pressure effects on the structure of silica after successive compression decompression experiments are analyzed. The mode Gruneisen parameters corresponding to the elastic compression of high density amorphous silica are obtained and compared with those of normal silica. A reorganization of the high density amorphous silica below 3 GPa is evidenced.

Polyamorphism is defined as the possibility for an amorphous material to exist with different structures. This has been demonstrated in solids for ice [O. Mishima, Y. Suzuki, Nature 419 (2002) 599], amorphous silicon [P.F. McMillan, M. Wilson, D. Daisenberger, D. Machon, Nature 4 (2005) 680], amorphous germanium and several oxide glasses [M. Grimsditch, Phys. Rev. 52 (1984) 2379, J.P. Itie, A. Polian, G. Calas, J. Petiau, A. Fontaine, H. Tolentino, Phys. Rev. 63 (1989) 398, C.H. Polsky, K.H. Smith, G.H. Wolf, J. Non-Cryst. Solids 248 (1999) 159, J. Nicholas, S Sinogeikin, J. Kieffer, J. Bass, Phys. Rev. Lett. 92 (2004) 215701, O. Majerus, L. Cormier, J.P. Itie, L Galoisy, D.R. Neuville, G. Calas, J. Non-Cryst. Solids 345&346 (2004) 34]: SiO2, GeO2, B2O3, SiO2–GeO2. Here we discuss the hysteresis curves corresponding to the evolution of the Raman bands as function of pressure for oxide glasses and compare it with ab-initio or molecular dynamics simulations [L. Huang, J. Kieffer, Phys. Rev. B 69 (2004) 224203, L. Huang, J. Kieffer, Phys. Rev. B 69 (2004) 244204, M. Durandurdu, Phys. Rev. B 73 (2006) 035209]. We show that these curves correspond for most of the glass studied to an irreversible change in the medium range order at ambient pressure. For a particular three component glass La2O3–B2O3–GeO2 (LBG) we demonstrate that this irreversibility occurs if the pressure is much higher than the in situ phase transformation pressure. It is predicted that this behaviour is general for glasses, leading to the possibility to recover new high density glass polymorphs in ambient conditions of temperature and pressure.

Densified silica can be obtained by different pressure and temperature paths and for different stress conditions, hydrostatic or including shear. The density is usually the macroscopic parameter used to characterize the different compressed silica samples. The aim of our present study is to compare structural modifications for silica glass, densified from several routes. For this, densified silica glasses are prepared from cold and high temperature (up to 1020 °C) compressions. The different densified glasses obtained in our study are characterized by micro-Raman spectroscopy. Intertetrahedral angles from the main band relative to the bending mode decrease and their values are larger for densified samples from high temperature compression than those samples from cold compression. The relative amount of 3-membered rings deduced from the D2 line area increases as a function of density for cold compression. The temperature increase during the compression process induces a decrease of the 3 fold ring population. Moreover, 3 fold rings are more deformed and stressed for densified samples at room temperature at the expense of those densified at high temperature. Temperature plays a main role in the reorganization structure during the densification and leads to obtaining a more relaxed structure with lower stresses than glasses densified from cold compression. The role of hydrostatic or non-hydrostatic applied stresses on the glass structure is discussed. From the Sen and Thorpe central force model, intertetrahedral angle average value and their distribution are estimated.

International audience; Modelling the mechanical response of silica glass is still challenging, due to the lack of knowledge concerning the elastic properties of intermediate states of densification. An extensive Brillouin Light Scattering study on permanently densified silica glasses after cold compression in diamond anvil cell has been carried out, in order to deduce the elastic properties of such glasses and to provide new insights concerning the densification process. From sound velocity measurements, we derive phenomenological laws linking the elastic moduli of silica glass as a function of its densification ratio. The found elastic moduli are in excellent agreement with the sparse data extracted from literature and we show that they do not depend on the thermodynamic path taken during densification (room temperature or heating). We also demonstrate that the longitudinal sound velocity exhibits an anomalous behavior, displaying a minimum for a densification ratio of 5% and highlight the fact that this anomaly has to be distinguished from the compressibility anomaly of a-SiO2 in the elastic domain.

Liquids in the system Y2O3 − Al2O3 have been the subject of considerable study because of the reported occurrence of a first-order density and entropy-driven liquid–liquid phase transition (LLPT) in the supercooled liquid state. The observations have become controversial because of the presence of crystalline material that can be formed simultaneously and that can mask the nucleation and growth of the lower density liquid. The previous work is summarized here along with arguments for and against the different viewpoints. Also two studies have been undertaken to investigate the LLPT in this refractory system with emphasis on determining the structure of unequivocally amorphous materials. These include the in situ high energy X-ray diffraction (HEXRD) of supercooled Y2O3 − Al2O3 liquids and the low frequency vibrational dynamics of recovered glasses. Many-body molecular dynamics simulations are also used to interpret the results of both studies. The HEXRD measurements, combined with aerodynamic levitation and rapid data acquisition techniques, show that for the 20 mol% Y2O3 (i.e. AlY20) liquid there is a shift in the position of the first peak in the diffraction pattern over a narrow temperature range (2100–1800 K) prior to crystallization. Microbeam Raman spectroscopy measurements made on AlY20 glasses clearly show contrasting spectra in the low frequency part of the spectrum for low- (LDA) and high-density (HDA) glassy regions. The molecular dynamics simulations identify contrasting coordination environments around oxygen anions for the high- (HDL) and low-density (LDL) liquids.

Glass formation, and associated potential polyamorphism are investigated for the key ceramic Y2O3-Al2O3 using a combination of experimental and theoretical techniques. Liquid samples are rapidly cooled by drop quenching and high and low density amorphous regions (LDA and HDA respectively) are identified using reflected light microscopy. Raman spectra are obtained to low frequency focussed on regions identified as pure LDA or HDA. The respective compositions of these regions are confirmed by electron microprobe analysis. These spectra are used to extract the vibrational densities of states and these are compared with those generated for the liquid oxide using polarizable-ion molecular dynamics simulations. The experimental and simulated spectra are used to determine the low temperature heat capacities. The low frequency regions of the spectra display an excess of states (boson peaks) which are different for the two glasses. Thermodynamic modelling is used to demonstrate how samples of the same composition my vitrify or not depending upon the quench rate.

International audience; Understanding the response of glasses to high pressure is of key importance for clarifying energy-dissipation and the origin of material damage during mechanical load. In the absence of shear bands or motile dislocations, pressure-induced deformation is governed by elastic and inelastic structural changes which lead to compaction of the glass network. Here, we report on a pressure-induced reconstructive amorphous-amorphous transition which was detected in sodium borosilicate glass by Raman and Brillouin scattering. The transition occurs through the formation of four-membered danburite-type rings of BO4 and SiO4-tetrahedra. We suggest that the inelastic pressure-resistance is governed by the Si-O-Si-backbone of the mixed borosilicate network. We further show that compaction is accompanied by increasing structural homogeneity and interpret this as a universal phenomenon in non-crystalline materials.

International audience; We investigate the specific optical regime occurring at short wavelengths, in the high absorption regime, in silicon thin-films patterned by periodically arranged nano-holes. Near-field scanning optical microscopy indicates that the incoming light is coupled to vertically channelling modes. Optical modelling and simulations show that the light, travelling inside the low-index regions, is absorbed at the direct vicinity of the nano-holes sidewalls. This channelling regime should be taken into account for light management in optoelectronic devices.

Glass formation, and associated potential polyamorphism are investigated for the key ceramic Y2O3–Al2O3 using a combination of experimental and theoretical techniques. Liquid samples are rapidly cooled by drop quenching and high and low density amorphous regions (LDA and HDA respectively) are identified using reflected light microscopy. Raman spectra are obtained to low frequency focussed on regions identified as pure LDA or HDA. The respective compositions of these regions are confirmed by electron microprobe analysis. These spectra are used to extract the vibrational densities of states and these are compared with those generated for the liquid oxide using polarizable-ion molecular dynamics simulations. The experimental and simulated spectra are used to determine the low temperature heat capacities. The low frequency regions of the spectra display an excess of states (boson peaks) which are different for the two glasses. Thermodynamic modelling is used to demonstrate how samples of the same composition my vitrify or not depending upon the quench rate.

The homogeneous/inhomogeneous structure of glasses is still a debated question. Hydrostatic high pressure experiments allow us to determine if a glass behaves as an elastic continuous random network or if a nanometer scale heterogeneity has to be taken into account. In order to get information on the homogeneous/inhomogeneous structure of glasses, in situ high pressure Raman experiments are performed on silica in the elastic domain up to 4.7 GPa. A strong decrease of the Boson peak intensity is observed between 1 bar and 3 GPa. We show that this decrease does not correspond quantitatively to the effect of pressure on a homogeneous elastic medium. From the interpretation of the narrowing of the main Raman band width under pressure as a narrowing of the θ inter-tetrahedral Si–O–Si angle distribution it is shown that the decrease of the Boson peak intensity is correlated to the decrease of the intrinsic inhomogeneity of the silica glass. These results confirm the occurrence of an intrinsic inhomogeneity at a nanometer scale even in a single component glass like SiO2 which is very important for the interpretation of the optical or mechanical properties of the glasses.

The microscopic origin of the excess of Density of Vibrational States (Boson peak) is discussed, taking into account recent analyses of the properties of glasses that were frozen-in under high pressure. Experimental data reveals a decrease of the Boson peak with increasing pressure of freezing (fictive pressure) and, simultaneously, an increase of the structural homogeneity of the glass. These results suggest new ways to improve the transmission of telecommunication fibers by decreasing the optical loss due to the scattering by the structural inhomogeneities of glasses.

Polyamorphic transitions in silica are studied under pressure up to 26.2 GPa by Raman and Brillouin spectrocopies. The first reversible polyamorphic transition is characterized by an abrupt decrease of the Si–O–Si inter-tetrahedral angle θ at 2.5 GPa corresponding to the elastic anomaly of silica. This result is interpreted as a reversible transition between two Low Density Amorphous phases LDA β ↔ LDA α similar to the β–α transition of cristobalite crystal under pressure. The second polyamorphic transition is observed for silica glass samples compressed up at different maximum pressures P max between 12 GPa and 26.2 GPa and recovered at ambient pressure. It corresponds to an irreversible and progressive transformation from the LDA α phase to a High Density Amorphous (HDA) phase. This HDA phase is characterized by an increase of the statistic distribution of 4- and 3-membered rings of SiO 4 tetrahedra with a narrowing of inter-tetrahedral angle distribution. A vanishing of the elastic anomaly in the HDA phase is observed.

In glass, starting from a dependence of the Angell's fragility on the Poisson ratio [V. N. Novikov and A. P. Sokolov, Nature 431, 961 (2004)], and a dependence of the Poisson ratio on the atomic packing density [G. N. Greaves, A. L. Greer, R. S. Lakes, and T. Rouxel, Nature Mater. 10, 823 (2011)], we propose that the heterogeneities are predominantly density fluctuations in strong glasses (lower Poisson ratio) and shear elasticity fluctuations in fragile glasses (higher Poisson ratio). Because the excess of low-frequency vibration modes in comparison with the Debye regime (boson peak) is strongly connected to these fluctuations, we propose that they are breathing-like (with change of volume) in strong glasses and shear-like (without change of volume) in fragile glasses. As a verification, it is confirmed that the excess modes in the strong silica glass are predominantly breathing-like. Moreover, it is shown that the excess breathing-like modes in a strong polymeric glass are replaced by shear-like modes under hydrostatic pressure as the glass becomes more compact.

International audience; In silicon-based solar cells, a substantial part of the energy losses is related to the charge carriers thermalization in the UV-blue range and the week carriers collection at these wavelenghts. To avoid this issue, we introduce a new concept which combines a rare-earths doped thin layer with a photonic crystal (PC) layer, allowing an efficient conversion from UV-blue photons to near-IR photons. We report on the feasibility of such a nanostructured down-converter module using an active rare-earth doped CaYAlO4 thin layer and a silicon nitride PC on top. By means of optical numerical simulations, the promising potentialities of the concept are demonstrated.

Using a combination of experimental techniques such as optical absorption, Raman scattering, continuous wave and pulse Electron Spin Resonance (ESR), we characterize a set of γ-irradiated Yb3+ doped silica glass preforms with different contents of phosphorous and aluminum. We demonstrate that when P is introduced in excess compared to Al, nearly no radiodarkening is induced by γ-rays. On the other hand, when Al>P, a large absorption band is induced by radiation. Thermal annealing experiments reveal the correlation between the decrease of the optical absorption band and the decrease of the Al-Oxygen Hole Center (AlOHC) ESR signal, demonstrating the main role of AlOHC defects in the fiber darkening. HYSCORE (HYperfine Sublevel CORElation) pulse-ESR experiments show a high Al-P nuclear spin coupling when P>Al and no coupling when Al>P. This result suggests that both AlOHC and POHC creation is inhibited by Al-O-P linkages. Confronting our data with previous works, we show that the well-known photodarkening process, meaning losses induced by the IR pump, can also be explained in this framework.

International audience; The elastic and plastic behaviors of silica glasses densified at various maximum pressure reached (12 GPa, 15 GPa, 19 GPa, and 22 GPa), were analyzed using in situ Raman and Brillouin spectroscopies. The elastic anomaly was observed to progressively vanish up to a maximum pressure reached of 12 GPa, beyond which it is completely suppressed. Above the elastic anomaly the mechanical behavior of silica glass, as derived from Brillouin measurements, is interpreted in terms of pressure induced transformation of low density amorphous silica into high density amorphous silica.

Using a combination of pulse electron paramagnetic resonance and photoluminescence spectroscopy, we demonstrate the major role of phosphorous rather than aluminium in the rare-earth dissolution process, an essential advance in telecommunication and solid laser fields. Our results also provide new insight into the micro-structural origin of the photodarkening process occurring in Yb doped fiber.

International audience; Micro-Raman spectroscopy was used to map the Vickers indentation-induced densification on a window glass (soda-lime silicate glass), from the correlation between Raman spectrum and density. Both top surface and cross-section of the residual imprints were investigated. It is shown that the sample preparation needed for the investigation of the in-depth densification does not alter the results. The maximum densification ratio measured is about 3.8%, which is 60% of the maximum densification measured after a high-pressure hydrostatic loading. Within the experimental errors, densification maps are self-similar for the two indentation loads used 10 N and 20 N. A comparison with finite element results based on a constitutive model developed for silica is discussed.

International audience; In addition of a flow, plastic deformation of structural glasses (in particular amorphous silica) is characterized by a permanent densification. Raman spectroscopic estimators are shown to give a full account of the plastic behavior of silica under pressure. While the permanent densification of silica has been widely discussed in terms of amorphous-amorphous transition, from a plasticity point of view, the evolution of the residual densification with the maximum pressure of a pressure cycle can be discussed as a density hardening phenomenon. In the framework of such a mechanical aging effect, we propose that the glass structure could be labelled by the maximum pressure experienced by the glass and that the saturation of densification could be associated with the densest packing of tetrahedra only linked by their vertices.

International audience; The in situ elastic and plastic behaviors of sodium aluminosilicate glasses with different degrees of depolymerization were analyzed using Brillouin spectroscopy. The observed elastic anomaly progressively vanished with depolymerization. The densification process appears to be different from that observed in pure silica glass. In the plastic regime of densified glasses hysteresis loops were observed and related to modification of the local silicon environment facilitated by the addition of sodium.

We present low-frequency Raman scattering of pure GeO(2) glass under pressure up to 4 GPa, corresponding to an elastic transformation. Intensity variation and frequency shift of the boson peak are analysed and compared to the Debye model. The decrease of the boson peak intensity scaled by the Debye energy is correlated to the elastic anomalous properties under pressure up to 1.5 GPa, and interpreted as an elastic homogenisation process at the local scale. We emphasize similarities between a-GeO(2) and a-SiO(2) behavior under pressure, and compare our results to other experiments, numerical studies, and predictions of several models concerning amorphous systems.

Raman micro-spectroscopy is used to analyse the plastic behaviour of window glass (a soda-lime silicate glass) under high hydrostatic pressure and Vickers indentation. We show pressure-induced irreversible structural changes, notably an increase of Q(2) species at the expense of Q(3). For the first time, a very accurate [Formula: see text] calibration curve has been established. Local density variations of a Vickers indented window glass have been characterized by micro-Raman mapping using a high spatial resolution device. The effects of glass depolymerization on indentation and hydrostatic compression are discussed. Differences between window glass and pure SiO(2) glass behaviour under high stresses are also highlighted and analysed at a local scale.

1 Surface du Verre et Interfaces, Unit e Mixte de Recherche CNRS/Saint-Gobain, 39, Quai Lucien Lefranc, 93303 Aubervilliers Cedex, France 2 Laboratoire PMMH, ESPCI/CNRS 10 rue Vauquelin 75231 Paris cedex 05, France 3 Laboratoire de Physico-Chimie des Materiaux Luminescents, UMR 5620 CNRS/Universit e Claude Bernard Lyon I, Domaine scientifique de la Doua, Bat Gabriel Lippmann, 12, rue A.M. Ampere 69622 Villeurbanne Cedex 4 LTDS UMR5513 CNRS/ECL/ENISE Ecole Nationale d’Ingenieurs de Saint-Etienne 58 rue Jean Parot F 42023 Saint-Etienne, France