A neutron diffraction study of sodium, rubidium and caesium borate glasses
A neutron diffraction investigation has been performed to investigate the effect of the network modifying cation fraction, x M, on the structure of a series of binary sodium, rubidium and caesium borate glasses. The first peak in the corrected, normalised diffraction pattern, I(Q), is employed to estimate the distance between the network modifying cations occupying adjacent network cages, and the fraction of 4-fold co-ordinated boron atoms, x4, is calculated from the area under the first (B–O) peak in the real-space correlation function, T(r). Up to the di-pentaborate composition, 2M2O.5B2O3 (M=Na, Rb or Cs), there is no evidence, within the experimental uncertainty, for significant numbers of nonbridging oxygen atoms. The fact that the first diffraction peak for the rubidium and caesium borate glasses remains sharp at low x M indicates that their structure is nanoheterogeneous, in agreement with the chemical structure predicted from thermodynamic modelling. The structure of the invert glass 2·13Rb2O.B2O3 includes tetrahedral borate structural units with nonbridging oxygen atoms, whereas that of vitreous 7Na2O.3B2O3 exhibits carbonate retention.
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Document Type: Research Article
Publication date: 01 April 2014