Ref HAL: hal-00182371_v1
PMID 21690784
DOI: 10.1088/0953-8984/18/17/018
WoS: 000238354300022
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22 Citations
Résumé:

Al1-xGaxPO4 solid solutions (x = 0.2, 0.3, 0.38, 0.7) and the pure AlPO4 (x = 0) and GaPO4 (x = 1) end members with the α-quartz-type structure were studied by Raman scattering. An investigation as a function of composition enabled the various modes to be assigned, in particular coupled and decoupled vibrations. The tetrahedral tilting modes, which have been linked to high-temperature phase transitions to β-quartz-type forms, were found to be decoupled. In addition, it is shown that Raman spectroscopy is a powerful technique for determining the gallium content of these solid solutions. Single crystals with x = 0.2, 0.38, and 1.0 (GaPO4) were investigated at high temperature. The composition Al0.8Ga0.2PO4 was found to exhibit sequential transitions upon heating to the β-quartz and β-cristobalite forms at close to 993 K and 1073 K, respectively. Direct α-quartz–β-cristobalite transitions were observed for the two other compositions at close to 1083 K and 1253 K, respectively, upon heating. The spectra of the β-quartz and β-cristobalite forms indicate the presence of significant disorder. Back transformation to the α-quartz-type form occurred readily with a hysteresis of less than 100 K for the composition x = 0.38 and for pure GaPO4. Rapid cooling was necessary to obtain the metastable α-cristobalite form. In contrast, for Al0.80Ga0.20PO4, the α-cristobalite form was obtained even upon slow cooling.

Ref HAL: hal-00011136_v1
Ref Arxiv: cond-mat/0510266
Ref. & Cit.: NASA ADS
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Résumé:

In this paper, small-angle X-ray scattering measurements are used to determine the different compressibility contributions, as well as the isothermal compressibility, in thermal equilibrium in silica glasses having different thermal histories. Using two different methods of analysis, in the supercooled liquid and in the glassy state, we obtain respectively the temperature and fictive temperature dependences of the isotheraml compressibility. The values obtained in the glass and supercooled liquid states are very close to each other. They agree with previous determinations of the literature. The compressibility in the glass state slightly decreases with increasing fictive temperature. The relaxational part of the compressibility is also calculated and compared to previous determinations. We discussed the small differences between the different determinations.

Commentaires: accepte dans physical review B

Ref HAL: hal-00004494_v1
Ref Arxiv: cond-mat/0503439
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Résumé:

The temperature dependence of the x-ray scattering in the region below the first sharp diffraction peak was measured for silica glasses with low and high OH content (GE-124 and Corning 7980). Data were obtained upon scanning the temperature at 10, 40 and 80 K/min between 400 K and 1820 K. The measurements resolve, for the first time, the hysteresis between heating and cooling through the glass transition for silica glass, and the data have a better signal to noise ratio than previous light scattering and differential thermal analysis data. For the glass with the higher hydroxyl concentration the glass transition is broader and at a lower temperature. Fits of the data to the Adam-Gibbs-Fulcher equation provide updated kinetic parameters for this very strong glass. The temperature derivative of the observed X-ray scattering matches that of light scattering to within 14%.

Commentaires: EurophysicsLetters, in press