Probing oxide-based glass structures by solid-state NMR: Opportunities and limitations

BO3/BO4 Intermixing in Borosilicate Glass Networks Probed by Double-Quantum 11B NMR: What Factors Govern BO4–BO4 Formation?

“…The t 1 evolution period was preceded by a Hahn echo of duration 2τ r for ensuring rotorsynchronized 2QC excitation and reconversion stages. 60 The CT-selective 180°pulse of the echo segment was cycled in 8 steps to remove undesirable single-spin 2QCs associated with the STs; 59 [3] −O−B [3] , B [3] −O−B [4] , B [4] −O−B [4] 58 Then, multiple-11 B-spin effects are negligible, 62 and each I exp pq value is directly proportional to the number of B [p] −O−B [q] linkages in the glass, within two effects/features that must be corrected for: (i) The distinct average quadrupolar products 33 of the 11 B [3] (C Qη [3] ≈ 2.6 MHz) and 11 B [4] (C Qη [4] ≈ 0.4 MHz) sites, 58 which along well-documented 2Q dipolar-recoupling features of half-integer spins 75,79,80 lead to an underestimation (overestimation) of the number of B [4] −O−B [4] (B [3] −O−B [3] ) linkages in the glass network. 58 (ii) The identity x B pq = I exp pq also requires (on the average) equal internuclear 11 B [p] −O− 11 B [q] distances (r pq ) among all {pq} = {33, 34, 44} pairs.…”

“…The electropositive M + /M 2+ cations balance both the NBO anions and the negatively charged BO species of the [BO 4 ] − groups, which have led to the respective "network modifier" and "charge compensator" terminologies. 12,33 Note, however, that all M + /M 2+ cations also coordinate the formally chargeneutral BO atoms of Si−O [2] and B [3] −O [2] bonds. 28,29,71−73 For a clear-cut discrimination among the structural M z+ and F entities, we employ the old "network modifier" term when referring to the M + /M 2+ cations.…”

“…23−31 The three network-forming (F) species, B [3] , B [4] , and Si [4] �where each superscript denotes the coordination number with respect to O (i.e., the number of F−O bonds)�interlink by bridging O (BO) atoms (O [2] coordinations) to form a BS glass network of BO 3 , BO 4 , and SiO 4 moieties. MO z/2 −B 2 O 3 −SiO 2 glasses with extensive amounts of electropositive M z+ cations ("network modifiers") also reveal nonbridging O (NBO; O − ) anions, each located at an FO p polyhedron via a covalent F [p] −O − bond that is charge-balanced further by the M z+ species 12,32,33 (see Section 2).…”

“…The short-range (≲0.3 nm) structures of borate/BS-based glasses have remained extensively investigated over decades, primarily by Raman – and solid-state nuclear magnetic resonance (NMR) ,– spectroscopies and more recently also by molecular dynamics (MD) simulations. – The three network-forming ( F ) species, B [3] , B [4] , and Si [4] where each superscript denotes the coordination number with respect to O (i.e., the number of F–O bonds)interlink by bridging O (BO) atoms (O [2] coordinations) to form a BS glass network of BO 3 , BO 4 , and SiO 4 moieties. MO z /2 –B 2 O 3 –SiO 2 glasses with extensive amounts of electropositive M z + cations (“network modifiers”) also reveal nonbridging O (NBO; O – ) anions, each located at an F O p polyhedron via a covalent F [ p ] –O – bond that is charge-balanced further by the M z + species ,, (see Section ).…”

Cation field‐strength effects on ion irradiation‐induced mechanical property changes of borosilicate glass structures

“…They may act either as "charge compensators," which balance the negative charge of the [BO 4 ]tetrahedra, or as network modifiers, which compensate the non-bridging oxygen (NBO; O -) ions; these negative species stem from BO 3 → [BO 4 ]and BO → NBO conversions, respectively, where the former normally prevails in BS glasses with low M z+ contents. 4,[10][11][12][13][14][15] Desirable physical and chemical properties of a borosilicate glass may be tailored by varying its oxide contents and/or the type of M z+ cation. 4,8,12 For example, BS glasses with a minor P doping but large modifier contents possess fragmented networks that readily dissolve in body fluids, thereby being promising for biomedical implants, [16][17][18][19][20] while lanthanide-cation-bearing glasses exhibit luminescence and are potential candidates for glass scintillators.…”