Ref HAL: hal-00504419_v1
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The short- and long-range structure of a series of single and mixed aluminophosphate glasses with the general composition [xNa(2)O (46-x)Li2O], [y,Al2O3 (54 -y)P2O5] is analyzed using P-31 and Al-21 magic-angle spinning (MAS) NMR as well as small-angle X-ray scattering. These series of glasses allow analyzing both the effect of alumina incorporation in these glasses, for small alumina content (y = 0, 4, 8). and the structural changes associated with the so-called mixed alkali effect (,v = 0, 11.5, 23, 34.5, 46). Our results indicate that aluminum is mainly octalledrally coordinated in these glasses and that there is most likely some segregation of the Al(OP)(6) species. In the pure phosphate glasses, we observe a "classical" continuous variation of the structural properties with the relative alkali content, but in the aluminophosphate, both local and long-range structural results reveal for the first time some nonlinear change as a function of the relative alkali content.

Ref HAL: hal-00109714_v1
Ref Arxiv: cond-mat/0610693
DOI: 10.1103/PhysRevB.74.224202
WoS: 000243195600030
Ref. & Cit.: NASA ADS
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3 Citations
Résumé:

Comparison of the internal friction at hypersonic frequencies between a few K and the glass transition temperature Tg for various glasses brings out general features. At low temperature, internal friction is only weakly dependent on the material. At high temperature but still below Tg the internal friction for strong glasses shows a T-independent plateau in a very wide domain of temperature; in contrast, for fragile glass, a nearly linear variation of internal friction with T is observed. Anharmonicity appears dominant over thermally activated relaxational processes at high temperature.

Commentaires: accepted in Physical Review B

Ref HAL: hal-00016521_v1
Ref Arxiv: cond-mat/0601096
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In order to clarify the origin of the dominant processes responsible for the acoustic attenuation of phonons, which is a much debatted topic, we present Bril louin scattering experiments in various silica glasses of different OH impurities content. A large temperature range, from 5 to 1500 K is investigated, up to the glass transition temperature. Comparison of the hypersonic wave attenuation in various samples allows to identify two different processes. The first one induce s a low temperature peak related to relaxational processes; it is strongly sensitive to the extrinsic defects. The second, dominant in the hig h temperature range, is weakly dependent on the impurities and can be ascribed to anharmonic interactions.

Ref HAL: hal-00109830_v1
Ref Arxiv: cond-mat/0610698
DOI: 10.1016/j.jnoncrysol.2006.02.135
WoS: 000242821800020
Ref. & Cit.: NASA ADS
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32 Citations
Résumé:

We studied a set of float glass samples prepared with different fictive temperature by previous annealing around the glass transition temperature. We compared the results to previous measurements on a series of amorphous silica samples, also prepared with different fictive temperature. We showed that the modifications on the structure at a local scale are very small, the changes of physical properties are moderate but the changes on density fluctuations at a nanometer scale are rather large: 12 and 20% in float glass and silica, for relative changes of fictive temperature equal to 13 and 25% respectively. Local order and mechanical properties of silica vary in the opposite way compared to float glass (anomalous behavior) but the density fluctuations in both glasses increase with temperature and fictive temperature.

Ref HAL: hal-00109721_v1
Ref Arxiv: cond-mat/0607233
DOI: 10.1088/0953-8984/188/32/001
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Résumé:

In order to point out the influence of thermal history (fictive temperature) and OH content on the elastic properties of silica glass, we have performed high resolution in situ Brillouin spectra of SiO2 glass from room temperature to the supercooled liquid at 1773K across the glass transition. The well known anomalous increase of elastic modulus in the glassy state and in the supercooled liquid regime is observed. No change of slope in the elastic moduli of silica appears as a characteristic of glass transition, on the contrary to what happens in various other glasses. We show that thermal history has a weak effect on elastic moduli in the glass transition regime for silica glass. The effect of water content in silica glass is more efficient than the fictive temperature effect and gives larger changes in the amplitude of elastic modulus for the same thermal dependence. A singular decrease above 1223K is also observed in the shear moduli for hydrated samples. Different models explaining elastic properties temperature dependence in relationship with frozen-in density fluctuations or with the structure are discussed.

Commentaires: 22pages, 11 figures