NMR studies of the structure of alkali thioborate glasses

Abstract

<p>The [superscript]11B NMR spectra of high purity xNa[subscript]2S + (1-x)B[subscript]2S[subscript]3 glasses (where 0 ≤ x ≤ 0.8), xK[subscript]2S + (1-x)B[subscript]2S[subscript]3 glasses (where 0 ≤ x ≤ 0.45), and mixed alkali x(Na[subscript]2S:K[subscript]2S) + (1-x) B[subscript]2S[subscript]3 glasses (where 0 ≤ x ≤ 0.25) are reported. The [superscript]11B NMR spectrum of vitreous B[subscript]2S[subscript]3 consists of a quadrupolar broadened single line and confirms a short range order of trigonally coordinated borons. As in the oxide analogs, as alkali sulfide is added, a single narrow peak grows in at the resonance frequency, confirming the existence of highly symmetric tetrahedrally coordinated borons;The fractions of tetrahedral borons that are created in the low alkali region by the addition of Na[subscript]2S to B[subscript]2S[subscript]3 are found to be a factor of three to four times greater at a given composition than those observed in the Na[subscript]2O + B[subscript]2O[subscript]3 system. A structural model has been developed in an attempt to explain these high tetrahedral boron fractions;In the K[subscript]2S + B[subscript]2S[subscript]3 system, tetrahedral boron fractions also found to be a factor of one and one half times greater than those in the K[subscript]2O + B[subscript]2O[subscript]3 system. A structural model has been developed in order to explain this behavior;The mixed alkali glasses are found to contain fractions of tetrahedral borons that fall on the average values of single alkali glasses having the same total alkali content. This is in contrast to alkali borate mixed alkali glasses, in which tetrahedral boron fractions tend to be lower than the average values of the single alkali glasses.</p>