Intermediate range order in ( Fe , Al ) silicate network glasses : a neutron diffraction and EPSR modeling
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چکیده
The local structural environment and the spatial distribution of iron and aluminum ions in sodosilicate glasses with composition NaFexAl1-xSi2O6 (x = 1, 0.8, 0.5 and 0) is studied by highresolution neutron diffraction combined with structural modeling using the Empirical Potential Structure Refinement (EPSR) code. This work gives evidence of differences in the structural behavior of Al and Fe, which are both often considered to act as network formers in chargebalanced compositions. The short-range environment and the structural role of the two cations are not composition dependent, and hence the structure of intermediate glasses can then be seen as a mixture of the structures of the two end-members. All Al is 4-coordinated for a distance ! d [ 4] Al 3+ "O =1.76 ± 0.01Å . The high-resolution neutron data allows deciphering between two populations of Fe. The majority of Fe is 4-coordinated ( ! d [ 4] Fe 3+ "O =1.87 ± 0.01Å ) while the remaining Fe and all Fe (∼12% of total Fe) are 5-coordinated ( ! d [ 5] Fe"O = 2.01± 0.01Å). Both AlO4 and FeO4 are randomly distributed and connected with the silicate network in which they share corners with SiO4 tetrahedra, in agreement with a network-forming role of those species. On the contrary FeO5 tends to form clusters and to share edges with each other. 5-coordinated Fe is interpreted as network modifier and it turns out that, even if this coordination number is rare in crystals, it is more common in glasses in which they can have a key role on physical properties. ha l-0 02 78 40 9, v er si on 1 13 M ay 2 00 8
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تاریخ انتشار 2008