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A neutron-diffraction study of the crystal structure of analcime, NaAlSi 2 O 6 · H 2 O

1972; De Gruyter; Volume: 135; Issue: 3-4 Linguagem: Inglês

10.1524/zkri.1972.135.3-4.240

2366-1798

Giovanni Ferraris, D. W. Jones, J. Yerkess,

Clay minerals and soil interactions

The crystal structure of the mineral analcime, NaAlSi2O6 · H2O, known from x-ray analysis to approximate closely to the cubic space-group symmetry Ia3d, has been examined by neutron diffraction. Intensity data from a single crystal were collected for one octant so as to be representative of cubic and some lower symmetries. In general, the systematic absences were consistent with the space group Ia3d; within experimental error, the six reflections equivalent for Laue group m3m were equal in intensity. From Fourier difference syntheses and least-squares refinements, it is concluded that the neutron data, like the x-ray data, are consistent with an averaged Ia3d structure. Full-matrix least-squares refinement with the constraints required by the Ia3d space group gave a final R value of 0.044 over 194 independent reflections. Hydrogen atoms are distributed in 32e and 96h positions and are not engaged in hydrogen bonds. Apparent values for the H–O–H angle probably depend on the averaging of arrangements for the water molecules; interpretations are suggested in terms of static and dynamic models.