Structure from glass to melt: a case study along the MgSiO3_{{3}}–CaSiO3_{{3}} join using neutron and X-ray diffraction

Glass and melt structures are inherently complex and disordered with significant changes expected to occur with temperature. In the present paper, a comparison of the structure of glasses and liquids along the MgSiO3–CaSiO3 join is carried out using neutron and X-ray diffraction (XRD). Empirical Potential Structure Refinement (EPSR) simulations were used to fit the experimental data. The average coordination number (CN) and site distribution is obtained for Mg and Ca showing distinct sites between the two cations and higher coordinated sites in the liquids. The major glass to melt modifications is observed at the scale of intermediate range order (IRO) by rearrangement of the (Ca,Mg)–Si and (Ca,Mg)–(Ca,Mg) connections. The structural evolution with temperature, especially concerning the cationic environments, illustrates the differences between glass and melt organization. These changes highlight the important contribution of cations to thermodynamical properties, diffusion and glass forming ability

Structure from glass to melt: a case study along the MgSiO3_{{3}}–CaSiO3_{{3}} join using neutron and X-ray diffraction

Glass and melt structures are inherently complex and disordered with significant changes expected to occur with temperature. In the present paper, a comparison of the structure of glasses and liquids along the MgSiO3–CaSiO3 join is carried out using neutron and X-ray diffraction (XRD). Empirical Potential Structure Refinement (EPSR) simulations were used to fit the experimental data. The average coordination number (CN) and site distribution is obtained for Mg and Ca showing distinct sites between the two cations and higher coordinated sites in the liquids. The major glass to melt modifications is observed at the scale of intermediate range order (IRO) by rearrangement of the (Ca,Mg)–Si and (Ca,Mg)–(Ca,Mg) connections. The structural evolution with temperature, especially concerning the cationic environments, illustrates the differences between glass and melt organization. These changes highlight the important contribution of cations to thermodynamical properties, diffusion and glass forming ability

The Structural Properties of Cations in Nuclear Glasses

International audienceThe structure of nuclear glasses and of simplified surrogates has been investigated using complementary diffraction and spectroscopic methods, together with numerical modeling. The diversity of structural surroundings of cations in glasses is reviewed at various scales. Cations usually occur in smaller sites in glasses than in crystals, with unusual site geometries such as 5-coordination. These sites may correspond to different structural positions. Network forming and networking situations illustrate the existence of a well-defined relationship with the glassy network, with cations improving glass stability. The complementary charge-compensation may sometimes give rise to a competition between cations. In that case, the cation may lose its stabilizing character and become a nucleating agent, as observed for “chameleon” elements, the coordination of which and hence the structural properties may change as a function of glass composition. Eventually, at the mesoscale, the heterogeneous distribution of cations has been recently visualized, providing keys to understand the nucleation processes in glasses

Color-center production and recovery in electron-irradiated magnesium aluminate spinel and ceria

International audienceSingle crystals of magnesium aluminate spinel (MgAl2O4) with (1 0 0) or (1 1 0) orientations and cerium dioxide or ceria (CeO2) were irradiated by 1.0 MeV and 2.5 MeV electrons in a high-fluence range. Point-defect production was studied by off-line UV-visible optical spectroscopy after irradiation. For spinel, regardless of both crystal orientation and electron energy, two characteristic broad bands centered at photon energies of 5.4 eV and 4.9 eV were assigned to F and F(+) centers (neutral and singly ionized oxygen vacancies), respectively, on the basis of available literature data. No clear differences in color-center formation were observed for the two crystal orientations. Using calculations from displacement cross sections by elastic collisions, these results are consistent with a very large threshold displacement energy (200 eV) for oxygen atoms at room temperature. A third very broad band centered at 3.7 eV might be attributed either to an oxygen hole center (V-type center) or an F2 dimer center (oxygen di-vacancy). The onset of recovery of these color centers took place at 200 °C with almost full bleaching at 600 DC. Activation energies (~0.3-0.4 eV) for defect recovery were deduced from the isochronal annealing data by using a first-order kinetics analysis. For ceria, a sub-band-gap absorption feature, which peaked at ~3.1 eV, was recorded for 2.5 MeV electron irradiation only. Assuming a ballistic process, we suggest that the latter defect might result from cerium atom displacement on the basis of computed cross sections

Colour centre recovery in yttria-stabilised zirconia: photo-induced versus thermal processes

International audienceThe photo-annealing of colour centres in yttria-stabilized zirconia (YSZ) was studied by electron paramagnetic resonance spectroscopy upon UV-ray or laser light illumination, and compared to thermal annealing. Stable hole centres (HCs) were produced in as-grown YSZ single crystals by UV-ray irradiation at room temperature. The numbers of HCs decays to non-zero asymptotic values when UV light is set off. The HCs produced by 200-MeV Au ion irradiation are partially bleached by UV light, whereas the F$^+$-type centres (involving oxygen vacancies) were left unchanged. In contrast, a significant photo-annealing of the latter point defects was achieved in 1.4-MeV electron-irradiated YSZ by 553-nm laser light irradiation, inside the absorption band of F$^+$-type centres centred at a wavelength $\sim$550 nm. Thermal annealing of F$^+$-type centres was also followed by UV-visible absorption spectroscopy. Almost complete photo-bleaching by laser irradiation was achieved like for thermal bleaching at $\sim$500K. Kinetic rate models of colour-centre evolution are proposed for the photo-induced processes and correlated to the thermally-activated ones

Lithium borate crystals and glasses: How similar are they? A non-resonant inelastic X-ray scattering study around the B and O K -edges

International audienceThe local environment of lithium borate glasses and their crystalline counterparts is investigated using non-resonant inelastic X-ray scattering (NRIXS) at energy losses corresponding to the B and O K-edges. Thanks to an extended series of lithium borate glasses and crystals, we have been able to finely interpret the local environments around boron and oxygen atoms in terms of coordination number, degree of polymerization of the borate network, superstructural units, and formation of non-bridging oxygens (NBOs). Even if a good local structural agreement between the glass and the crystal is found, an important structural discrepancy is found around the metaborate composition (50.mol% of Li 2 O) rendering useless the use of the crystalline phase to describe the glassy state. In low alkali glasses, two subnetworks corresponding to a 'Li-rich' domain and a pure B 2 O 3 domain containing boroxol rings have been evidenced. A spectral signature of the NBOs has also been evidenced in the p* peak of the B K-edge, making NRIXS a useful method offering a series of spectral signatures which can be used as structural probes for up-coming high-temperature or high-pressure in-situ experiments

Polymerized 4-Fold Coordinated Carbonate Melts in the Deep Mantle

International audienceOur understanding of the deep carbon cycle has witnessed amazing advances in the last decade, including the discovery of tetrahedrally coordinated high pressure (P) carbonate phases. However, little is known about the physical properties of their molten counterpart at moderate depths, while their properties at lower mantle conditions remain unexplored. Here, we report the structure and density of FeCO3 melts and glasses from 44 to 110 GPa by means of in situ x-ray synchrotron diffraction, and ex situ Raman and x-ray Raman spectroscopies. Carbon is fully transformed to 4-fold coordination, a bond change recoverable at ambient P. While low P melts react with silica, resulting in the formation of silico-carbonate glasses, high P melts are not contaminated but still quench as glasses. Carbonate melts are therefore polymerized, highly viscous and poorly reacting with silicates in the lower mantle, in stark opposition with their low P properties

Unexpected intracellular biodegradation and recrystallization of gold nanoparticles

International audienceGold nanoparticles are used in an expanding spectrum of biomedical applications. However, little is known about their long-term fate in the organism as it is generally admitted that the inertness of gold nanoparticles prevents their biodegradation. In this work, the biotransformations of gold nanoparticles captured by primary fibroblasts were monitored during up to 6 mo. The combination of electron microscopy imaging and transcriptomics study reveals an unexpected 2-step process of biotransformation. First, there is the degradation of gold nanoparticles, with faster disappearance of the smallest size. This degradation is mediated by NADPH oxidase that produces highly oxidizing reactive oxygen species in the lysosome combined with a cell-protective expression of the nuclear factor, erythroid 2. Second, a gold recrystallization process generates biomineralized nanostructures consisting of 2.5-nm crystalline particles self-assembled into nanoleaves. Metallothioneins are strongly suspected to participate in buildings blocks biomineralization that self-assembles in a process that could be affected by a chelating agent. These degradation products are similar to aurosomes structures revealed 50 y ago in vivo after gold salt therapy. Overall, we bring to light steps in the lifecycle of gold nanoparticles in which cellular pathways are partially shared with ionic gold, revealing a common gold metabolism

Assessment of Transition Element Speciation in Glasses Using a Portable Transmission Ultraviolet–Visible–Near-Infrared (UV-Vis-NIR) Spectrometer

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Uptake of Functionalized Mesoporous Silica Nanoparticles by Human Cancer Cells

International audienceMesoporous silica nanoparticles (MSN) were functionalised by aminofluorescein (AMF) with diethylenetriaminepentaacetic acid spacer molecules which provide free carboxylic groups for binding cell-specific ligands such as folate. AMF allowed the exploration of cellular uptake by HeLa cells using confocal microscopy and flow cytometry. The functionalized nanoparticles (MSN-AMF) penetrated efficiently into HeLa cell cytoplasm through a clathrin dependent endocytosis mechanism. The number of endocytosed MSN-AMF was enhanced when using folate as a targeting molecule. Uptake kinetics revealed that most of MSN-AMF were internalized within 4 h of incubation. Moreover, we found that MSN-AMF were capable of escaping the acidic endolysosomal vesicles of HeLa cells. Cytotoxicity studies suggested that these nanoparticles are non-toxic to HeLa cells up to a dose level of 50 mu g/ml