Structure of diopside, enstatite and magnesium aluminosilicate glasses: A joint approach using neutron and x-ray diffraction and solid-state NMR

Hesameddin Mohammadi, Rita Mendes Da Silva, Anita Zeidler, Lawrence V. D. Gammond, Florian Gehlhaar, Marcos de Oliveira Jr, Hugo Damasceno, Hellmut Eckert, Randall E. Youngman, Bruce G. Aitken, Henry E. Fischer, Holger Kohlmann, Laurent Cormier, Chris J Benmore, Philip Salmon

Research output: Contribution to journalArticlepeer-review

Abstract

Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and 29Si, 27Al, and 25Mg solid-state nuclear magnetic resonance (NMR) spectroscopy were used to measure the structure of glassy diopside (CaMgSi2O6), enstatite (MgSiO3), and four (MgO)x(Al2O3)y(SiO2)1-x-y glasses, with x = 0.375 or 0.25 along the 50 mol. % silica tie-line (1 - x - y = 0.5) or with x = 0.3 or 0.2 along the 60 mol. % silica tie-line (1 - x - y = 0.6). The bound coherent neutron scattering length of the isotope 25Mg was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline 25MgO. The diffraction results for the glasses show a broad asymmetric distribution of Mg-O nearest-neighbors with a coordination number of 4.40(4) and 4.46(4) for the diopside and enstatite glasses, respectively. As magnesia is replaced by alumina along a tie-line with 50 or 60 mol. % silica, the Mg-O coordination number increases with the weighted bond distance as less Mg2+ ions adopt a network-modifying role and more of these ions adopt a predominantly charge-compensating role. 25Mg magic angle spinning (MAS) NMR results could not resolve the different coordination environments of Mg2+ under the employed field strength (14.1 T) and spinning rate (20 kHz). The results emphasize the power of neutron diffraction with isotope substitution to provide unambiguous site-specific information on the coordination environment of magnesium in disordered materials.

Original languageEnglish
Article number214503
Number of pages23
JournalJournal of Chemical Physics
Volume157
Issue number21
Early online date2 Dec 2022
DOIs
Publication statusPublished - 7 Dec 2022

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