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Structural elucidation of β-(Y,Sc) 2 Si 2 O 7 : combined use of 89 Y MAS NMR and powder diffraction

2011; Wiley; Volume: 44; Issue: 4 Linguagem: Inglês

10.1107/s0021889811021303

1600-5767

Mathieu Allix, María D. Alba, Pierre Florian, Alberto J. Fernández–Carrión, Matthew R. Suchomel, Alberto Escudero, Emmanuelle Suard, Ana Isabel Becerro,

Glass properties and applications

Although the structures of pure Sc 2 Si 2 O 7 and β-Y 2 Si 2 O 7 have been described in the literature using the C 2/ m space group, 29 Si magic angle spinning (MAS) NMR measurements of the intermediate members of the Sc 2 Si 2 O 7 –β-Y 2 Si 2 O 7 system indicate a lowering of the symmetry to the C 2 space group. Indeed, these compositions exhibit a unique Si crystallographic site and an Si—O—Si angle lower than 180°, incompatible with the C 2/ m space group. C 2 is the only possible alternative. Space group Cm can be discarded with regard to its two different Si sites per unit cell. Moreover, 89 Y MAS NMR data have revealed the existence of two different Y sites in the structure of the intermediate members of the Sc 2 Si 2 O 7 –β-Y 2 Si 2 O 7 system, confirming the lowering of the symmetry to the C 2 space group. The viability of the C 2 model has therefore been tested and confirmed by refinement of synchrotron and neutron powder diffraction data for the different members of the system. The structural evolutions across the Sc 2 Si 2 O 7 –β-Y 2 Si 2 O 7 system are discussed.