Phase Transformations in Gel-Derived and Mixed-Powder-Derived Yttrium Disilicate, Y2Si2O7, by X-Ray Diffraction and 29Si MAS NMR
✍ Scribed by Julien Parmentier; Philippe R. Bodart; Ludovic Audoin; Georges Massouras; Derek P. Thompson; Robin K. Harris; Paul Goursat; Jean-Louis Besson
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 129 KB
- Volume
- 149
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
The di4erent polymorphs of Y 2 Si 2 O 7 have been synthesized by a sol+gel process and by mixed-powder routes. Their ranges of stability are discussed as a function of heat-treatment and synthesis route. It appeared that amorphous sol+gel samples crystallized according to the sequence amorphousP P P , even when isothermal heat-treatments were performed, regardless of temperature. It is proposed that preferential crystallization of is related to the type of silicon structural units in the starting amorphous precursor similar to phase. High-resolution 29 Si NMR spectra (linewidth421 Hz) are reported for the , , , and , polymorphs which are consistent with accepted structural data from the point of view of the number of sites, the populations, and the relative chemical shifts.