Structural Studies of Rare Earth-Doped Fluoroborosilicate Glasses by Advanced Solid-State NMR
Xuyang Zhang, Lili Hu, Jinjun Ren
Abstract
The detailed local structures of fluoroborosilicate glasses with the compositions of (50 + x)SiO2–(20 – x)B2O3–10Na2O–10NaF–10YF3 (x = 0, 5, 10, 15 mol %) were investigated by advanced one- and two-dimensional solid-state nuclear magnetic resonance (SSNMR) techniques. The borosilicate glass network is characterized by 29Si and 11B magic angle spinning NMR (MAS NMR) spectra. 29Si MAS spectra show that the silicate network strengthens with the decrease of the B2O3 content. Two three-coordination boron species (B(3)-ring, B(3)-nonring) and two four-coordination boron species (BO4, BO3F) are observed in the 11B MAS spectra. The two types of B(4) species are identified by 11B triple-quantum magic angle spinning (TQMAS) and J-coupling-based 11B{19F} heteronuclear multiple quantum coherence (J-HMQC) methods. The F– species are confirmed by 19F MAS spectra and a 19F{23Na} rotational echo double resonance (REDOR) method, revealing the existence of Na–F–B and multiple Na–F–Y linkages. The clustering of F– ions is proved by 19F static spin echo results, which indicate that B3+ ions have a dispersive effect on F– ions. 11B/23Na REDOR results show that the distribution of Na+ around B(3) and B(4) is similar, and independent of the content of B2O3. On the basis of these results, a quantitative atomic structure evolution with glass compositions is investigated.