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dc.contributor.authorGriffin, John Matthew
dc.contributor.authorBerry, Andrew J.
dc.contributor.authorFrost, Daniel J.
dc.contributor.authorWimperis, Stephen
dc.contributor.authorAshbrook, Sharon Elizabeth
dc.identifier.citationGriffin , J M , Berry , A J , Frost , D J , Wimperis , S & Ashbrook , S E 2013 , ' Water in the Earth's mantle : a solid-state NMR study of hydrous wadsleyite ' , Chemical Science , vol. 4 , no. 4 , pp. 1523-1538 .
dc.identifier.otherORCID: /0000-0002-4538-6782/work/56638929
dc.description.abstractWadsleyite, beta-(Mg,Fe)(2)SiO4, is the main component of the transition zone in the Earth's mantle, at depths of 410-530 km below the surface. This mineral has received considerable interest as a potential reservoir for the vast amount of hydrogen, as hydroxyl, referred to as water, that is thought to be contained within the mantle. However, the exact way in which water is incorporated into the structure of wadsleyite is not fully understood and has been the subject of considerable debate. In this work, O-17, Mg-25, Si-29, H-1 and H-2 solid-state NMR spectra were obtained from isotopically enriched samples of anhydrous and hydrous beta-Mg2SiO4. First-principles DFT calculations were also carried out for a range of model structures to aid interpretation of the experimental data. The results are consistent with a model for hydrous wadsleyite whereby hydrogen bonds to the O1 site to form hydroxyl groups that are charge balanced by cation vacancies on the Mg3 site. Structural models containing cation vacancies on the Mg2 site are found to be energetically less favourable and calculated NMR parameters show poor agreement with the experimental data. Disorder was also observed in the hydrous wadsleyite samples, and H-1 and H-2 NMR are consistent with not only Mg-O1-H but also more strongly hydrogen-bonded Si-O-H environments. These silanol protons can be incorporated into the structure with only a small increase in energy. Two-dimensional H-1-Si-29 and H-1-O-17 NMR correlation experiments confirm that the additional resonances do not correspond to Mg-OH protons and enable the identification of Si-29 and O-17 species within the Si-OH groups. This assignment is also confirmed by first-principles DFT calculations of NMR parameters. Silanol protons within Mg3 vacancies could account for up to 20% of the protons in the structure.
dc.relation.ispartofChemical Scienceen
dc.subjectStructural disorderen
dc.subjectQuantum MAS NMRen
dc.subjectO-17 NMRen
dc.subject1st-principles calculationsen
dc.subjectMagneium silicatesen
dc.subjectInteger quadropolar nucleien
dc.subjectInorganic materialsen
dc.subjectNominally anhydrous mineralsen
dc.subjectQ Scienceen
dc.titleWater in the Earth's mantle : a solid-state NMR study of hydrous wadsleyiteen
dc.typeJournal articleen
dc.contributor.sponsorThe Leverhulme Trusten
dc.contributor.institutionUniversity of St Andrews. EaSTCHEMen
dc.contributor.institutionUniversity of St Andrews. School of Chemistryen
dc.description.statusPeer revieweden
dc.identifier.grantnumberF/00 268/BJen

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