Contribution a l'etude des transitions de phase structurales des perovskites CsCaCl3 et CsPbCl3 par resonance paramagnetique electronique de l'ion Gd3+

SIGLECNRS T 59952 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Caractérisation multispectroscopique de l'ordre à moyenne distance dans des verres de phosphates

ORLEANS-BU Sciences (452342104) / SudocORLEANS-ISTO (452342307) / SudocSudocFranceF

Study of optical and mechanical properties of binary silicate glasses of heavy alkali

L étude présentée ici est consacrée à une approche expérimentale dans les verres silicatés d alcalins lourds : (SiO2)1-x(Rb2O)x et (SiO2)1-x(Cs2O)x. La polymérisation du réseau est dépendante de la composition du verre, la concentration en cation modificateur ainsi que sa nature vont donc être des facteurs importants influençant la topologie du réseau silicaté. Afin de mieux comprendre les propriétés de ces verres, il est indispensable d'en connaître la structure. Dans ce travail nous nous sommes particulièrement intéressés à l ordre à moyenne distance qui contrôle les propriétés mécaniques, et à l ordre à courte distance déterminant pour les propriétés optiques. La spécificité de ce travail réside dans la volonté comprendre le rôle des cations lourds sur la structure et les propriétés du réseau silicaté, dans les binaires alcalins, à l échelle macroscopique à l aide de diffusion Brillouin et à l échelle microscopique en utilisant les spectroscopies Raman et Infrarouge.The study presented here is devoted to an experimental approach in heavy alkali silicate glasses (SiO2)1-x (Rb2O)x and (SiO2)1-x (Cs2O)x. The polymerization of the network is dependent on glass composition, the modifier cation concentration and its nature will be important factors influencing the topology of the silicate network. To better understand the properties of these glasses, it is essential to know the structure. In this work we are particularly interested in the medium-range order, which controls the mechanical properties, and short-range order for determining the optical properties. The specificity of this work lies in the will understand the role of heavy cations on the structure and properties of silicate network in the binary alkali at the macroscopic scale using Brillouin scattering and microscopic scale using Raman and Infrared spectroscopy.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

Structural Relaxation Dynamics and Annealing Effects of Sodium Silicate Glass

International audienceHere we report high--precision measurements of structural relaxation dynamics in the glass transition range at the intermediate and short length scale for a strong sodium silicate glass during long annealing times. We evidence for the first time the heterogeneous dynamics at the intermediate range order by probing the acoustic longitudinal frequency in the GHz region by Brillouin light scattering spectroscopy. Or, from \textit{in--situ} Raman measurements we show that relaxation is indeed homogenous at the interatomic length scale. Our results show that the dynamics at the intermediate range order contains two distinct relaxation time scales, a fast and a slow component, differing by about a tenfold factor below $T_{g}$ and approaching to one another past the glass transition. The slow relaxation time agrees with the shear relaxation time, proving that Si--O bond breaking constitutes the primary control of structural relaxation at the intermediate range order

Heating Rate Effect on the Activation of Viscoelastic Relaxation in Silicate Glasses

AbstractHere we present a direct investigation of the heating rate effect on structural relaxation of sodium silicate glass near the glass transition by means of differential scanning calorimetry, and show the sensitivity of Brillouin light spectroscopy to the dynamic of structural relaxation in the medium range order (∼100nm)

Investigation of medium range order in silicate glasses by infrared spectroscopy

A new decomposition method of infrared spectra which takes into account the configurational and dynamical origins of the disorder allows retrieving structural information on short and medium range orders in potassium silicate glasses. The distribution of tetrahedral units, the occupation of cation sites, the ratio of SiO bond ionicities involving bridging and non bridging oxygen, and a measure of the impact of low frequency floppy modes on the high frequency dynamics are byproducts of the modeling process. The composition dependence of two vibrational modes clearly identified as spectral components signing medium range order, shows that the disruption of the silicate network follows selective schemes. The 3D silica like network completely disappears in glasses with K2O amounts greater than 11 mol% and above this threshold a progressive appearance of 2D silicate sheets is evidenced. © 2012 Elsevier B.V