Yann Vaills

A multispectroscopic study of PbOxZnO0.6−x(P2O5)0.4 glasses

Abstract The structure of ternary PbO x –ZnO (0.6− x ) –(P 2 O 5 ) 0.4 glasses has been investigated using nuclear magnetic resonance (NMR), Raman scattering and infrared spectroscopy (IR), over the compositional range from x =0 to 0.6. The evolution of the 31 P NMR chemical shift and Raman high-frequency modes reflects mainly the Zn/Pb substitution in these glasses. The NMR and Raman spectra show that at high ZnO content, the phosphate network has a strong interaction with Zn cations through P–O–Zn bonds. In glasses with high lead content, IR reflectivity spectra indicate that the phosphate network and lead cation are less correlated and that Pb 2+ has a mixed network former–network modifier role in the glass structure.

Two opposite effects of sodium on elastic constants of silicate binary glasses

(1 - x)SiO2-xNa2O glasses have been studied by Brillouin scattering when sodium oxide molar concentration x, varies in the range 0.05 < x < 0.44. Non-linear dependence of elastic constants on sodium oxide concentration is shown unambiguously for the first time and the compressive elastic constant C11 experienced a non-monotonic behaviour with a minimum value around x = 0.15. These results are compared with those obtained previously in the case of other alkali silicate glasses (Li, K). The variations of elastic constants of these glasses with the alkali metal nature and concentration are discussed on the basis of relations with the molar density of silicon atoms and the force constants between modifiers and non-bridging oxygens.

Elastic properties of sodium magnesium silica and sodium calcium silica glasses by brillouin scattering

Abstract In this article we present elastic constants measurements obtained by Brillouin scattering in sodium magnesium silica glasses. The results are compared with those known in sodium calcium silica glasses. Values and variations of elastic constants with the cationic Mg 2+ or Ca 2+ rate are discussed in term of middle range order.

Similarities in the behaviour of magnesium and calcium in silicate glasses

Abstract The dependence of the infrared reflection spectra of mixed sodium-alkaline earth-silicate glasses on magnesium or calcium content shows similarities. This is surprising in view of previous observations indicating a possible network-forming role for magnesium. In these glasses, a well localized band for calcium or magnesium is observed at frequencies similar to those found in CaO or MgO. However calculation of the effective charge carried by each type of cation gives a degree of ionicity, Z / Z 0 , of 0.9 for calcium but only 0.7 for magnesium. This difference explains why magnesium might have some network-forming character in alumino-silicate glasses.

Effects of thermal history on mechanical properties of (PbO)x(ZnO)(0.6−x)(P2O5)0.4 glasses using Brillouin scattering

Abstract The effects of temperature and annealing on mechanical properties of (PbO)x(ZnO)(0.6−x)(P2O5)0.4 glasses have been investigated using Brillouin scattering over the compositional range from x=0 to 0.6 between room temperature up to the softening point. The temperature dependence of the Brillouin frequency shift has permitted to determine the glass transition temperature and the softening point. The variations in these reference points and in the elastic constant C11 with lead content are correlated with chemical composition. The progressive replacement of zinc by lead cation corresponds to a decrease in the ability of the cation to cross-link between phosphate chains. This induces a decrease in the elastic constant and also in the glass transition temperature and the softening point.

Structural Relaxation Dynamics and Annealing Effects of Sodium Silicate Glass

Here 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 in-situ Raman measurements, we show that relaxation is indeed homogeneous 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 10-fold factor below Tg 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.

Dynamic behaviour of (1−x)SiO2-0.5xM2O glasses (M=Na, Li) investigated by infrared and Brillouin spectroscopies

Abstract Infrared reflectivity and Brillouin scattering investigations have been performed on alkali (Na, Li) silicate glasses of good optical quality, obtained from appropriate melts with cationic concentrations in the range 30–60%. The frequencies of vibrational modes have been extracted from fits of reflectivity spectra supplied by rapid-scan Fourier transform interferometry, while elastic constants were deduced from Brillouin scattering spectra obtained by high-resolution Fabry-Perot interferometry. Comparison of the results shows a correlation between the low-frequency vibrational cation mode and the elastic constant, C11, when the concentration or nature of the alkali cation change. An evolution of the covalent character of the bonds is displayed from measurement of the effective charge of oxygen.

Brillouin scattering in cubic phase of yttrium sesquioxide

Abstract A Brillouin scattering investigation has been performed in a Y2O3 single crystal, from room temperature up to 470 K. Elastic constant C11 and linear combination [ (C 11 + C 12 ) 2 + C 44 ] were measured and the C12 and C44 constants roughly estimated. The results are discussed in comparison with those obtained with α Al2O3.

WAXS and NMR studies of intermediate and short range order in K2O-SiO2 glasses

Abstract Wide-angle X-ray scattering and 29 Si NMR have been employed to investigate the medium-range structure of xK2O–(1−x)SiO2 glasses, with x varying in the limits 5% 1.4 A −1 A −1 range. The peaks broaden below x=20%, and at the lowest K2O fraction, a bimodal line shape is found. This broadening is interpreted in terms of phase separation at low K2O fraction. The NMR spectra consist of several (usually three) Gaussian components assigned to the different Q species (SiO4 tetrahedra with different connectivity) present. All three components are uniformly deshielded as K2O is incorporated into the structure. The fraction of non-bridging oxygens (NBOs) derived from the distribution of Q species matches the value obtained from the overall composition, except for the x=17.41% sample, again indicating phase-separation at x

Raman and Brillouin scattering and XPS spectroscopy in NaPb0.5Bi0.33PO4 glass: Evolution as a function of temperature

Abstract Raman spectra of glassy, recrystallised and liquid NaPb 0.5 Bi 0.33 PO 4 have been obtained in situ to a temperature of 1170 K. We analyze the modification of the spectra vs. temperature in terms of frequencies assigned to the cation vibrations and of frequencies assigned to PO 4 3− group vibrations, particularly the range 900–1200 cm −1 which was deconvoluted. Brillouin scattering experiments have been carried out between 298 K and the recrystallisation temperature. The temperature evolutions of the Brillouin frequencies and of the lowest Raman frequency exhibit the same dependence. Spectra obtained from X-ray Photoelectron Spectroscopy (XPS) revealed the existence of two lead and bismuth cations.