X-ray and neutron scattering study of the structure of lithium bismuth oxide glass

The structure of (100-x)Bi₂O₃·xLi₂O (25≤x≤35mol%) glasses has been investigated by means of X-ray and neutron scattering methods. Comparing the glasses with several bismuthate crystals in total correlation function T(r), it is concluded that a large amount of edge-sharing BiO_n polyhedra are present in the glasses and the network structure is similar to the Bi₂O₄ crystal. In the crystal, BiO₆ octahedra form a layer sharing their four corners mutually, and the BiO₄₊₄ distorted polyhedra are placed between the layers sharing all the edges with the neighboring polyhedra. Assuming two different Li sites in the Bi₂O₄-based structure, structural models were constructed to compare T(r), from which it was suggested that some Li ions substituted for the octahedral Bi site and some occupied an interstitial vacant site. In addition, the glasses have various defects such as excess O ions, positive-holes on O ions, vacant space to accept atmospheric oxygens, and Bi vacancies. The glass formation is sensitive to the melting conditions, such as temperature and period, suggesting that there exists some optimum quantity in the defect structures.