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

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

• Tipo de documento: Artigo Científico
• Fonte: Journal of Chemical Physics; v. 157, n. 21, p. 22-pg., 2022-12-07.

Resumo

Neutron diffraction with magnesium isotope substitution, high energy x-ray diffraction, and Si-29, Al-27, and Mg-25 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 Mg-25 was remeasured, and the value of 3.720(12) fm was obtained from a Rietveld refinement of the powder diffraction patterns measured for crystalline (MgO)-Mg-25. 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. Mg-25 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. (c) 2022 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/). (AU)

• Processo FAPESP: 13/07793-6 - CEPIV - Centro de Ensino, Pesquisa e Inovação em Vidros
• Beneficiário: Edgar Dutra Zanotto
• Modalidade de apoio: Auxílio à Pesquisa - Centros de Pesquisa, Inovação e Difusão - CEPIDs