title: Modifier cation effects on (29)Si nuclear shielding anisotropies in silicate glasses.
abstract: We have examined variations in the (29)Si nuclear shielding tensor parameters of SiO4 tetrahedra in a series of seven alkali and alkaline earth silicate glass compositions, Cs2O·4.81 SiO2, Rb2O·3.96 SiO2, Rb2O·2.25 SiO2, K2O·4.48 SiO2, Na2O·4.74 SiO2, BaO·2.64 SiO2, and SrO·2.36 SiO2, using natural abundance (29)Si two-dimensional magic-angle flipping (MAF) experiments. Our analyses of these 2D spectra reveal a linear dependence of the (29)Si nuclear shielding anisotropy of Q((3)) sites on the Si-non-bridging oxygen bond length, which in turn depends on the cation potential and coordination of modifier cations to the non-bridging oxygen. We also demonstrate how a combination of Cu(2+) as a paramagnetic dopant combined with echo train acquisition can reduce the total experiment time of (29)Si 2D NMR measurements by two orders of magnitude, enabling higher throughput 2D NMR studies of glass structure.
authors.affiliation: Division of Natural Science, Mathematics, and Nursing, Berea College, Berea, KY 40403, United States.
authors.forename: Jay H
authors.initials: JH
authors.lastname: Baltisberger
authors.affiliation: CNRS, UPR3079 CEMHTI, 1D Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Florian
authors.affiliation: Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States.
authors.forename: Eric G
authors.initials: EG
authors.lastname: Keeler
authors.affiliation: Division of Natural Science, Mathematics, and Nursing, Berea College, Berea, KY 40403, United States.
authors.forename: Pyae A
authors.initials: PA
authors.lastname: Phyo
authors.affiliation: Institut des Sciences Analytiques (CNRS, ENS de Lyon, UCB Lyon 1), Université de Lyon, 5 rue de la Doua, 69100 Villeurbanne, France.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Sanders
authors.affiliation: Department of Chemistry, The Ohio State University, 120 W. 18(th) Avenue, Columbus, OH 43210-1173, United States. Electronic address: grandinetti.1@osu.edu.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Grandinetti
keywords: (29)Si NMR; Akali silicate glass; Alkaline earth silicate glass; Echo train acquisition; Magic-angle flipping; Nuclear shielding tensor; Paramagnetic relaxation enhancement; Silicate disproportionation