Distribution of Modifier Cations and Network Polyhedra in Alkali Borogermanate Glasses

Alkali borogermanate glasses are topologically complex, in that [BOn] (n = 3, 4) and [GeOn] (n = 4, 5, 6) polyhedra may all coexist. Equilibrium between these structural units has significant influence on optical properties such as optical nonlinearity and lasing ions solubility. In previous work on the lithium and potassium systems, we used neutron diffraction and NMR to show that lithium borogermanate behaves like lithium borosilicate, and potassium borogermanate like sodium borosilicate. We now wish to repeat the study with the rubidium system where we wish to examine the coordination number models for borogermanate glasses when modified by much larger Group I rubidium cation.