Structure of Sodium Germanate Glasses over Very Wide Composition Range

Germanate glasses are of interest due to the germanate anomaly in the thermophysical properties, and the role that structure may play in this behaviour. There are still unresolved issues concerning the germanate anomaly, including the higher coordination (five or six?), evidence that the Ge-O bond length does not decrease at high modifier content even though germanium returns to pure tetrahedral coordination, and the “second anomaly” at low modifier content. Sodium germanates are the archetypal germanate glass-forming system, but have received little neutron diffraction attention. We have developed methods to make sodium germanate glasses over much wider composition range than hitherto available. Hence we seek GEM beamtime to study these samples, to shed light on the unresolved issues.