The structure of aluminate glasses by neutron diffraction

Pulsed neutron diffraction with high real-space resolution has been used to study the structure of two melt-quenched calcium aluminate, CaO–Al2O3, glasses containing 30 and 38 mol% Al2O3, respectively. The data show that aluminium is tetrahedrally coordinated by oxygen in these glasses, with a bond length 1.76 Å. There is no evidence for the presence of a fraction of aluminium atoms with a higher oxygen coordination number. The data also show that calcium is coordinated by four oxygen atoms at a well-defined interatomic distance of 2.34 Å. However, bond-valence calculations show that there must be an additional Ca–O coordination of at least two which occurs at a distance of 2.45 Å or greater.