Diffraction studies of glass structure: II. The structure of vitreous germania

Abstract

The effects of pile irradiation on the polymorphs of germania are described and it is shown that the structural effects are small. For the glass, density changes on irradiation are smaller than those resulting from different methods of preparation. The X-ray diffraction pattern of vitreous germania has been measured for Q between 0.8 and 16 Å −1. The experimental method and data reduction procedures are described. The structure of vitreous GeO 2 is discussed, using the correlation function D X( r) obtained by fourier transformation of the X-ray intensity data. This is compared with correlation functions derived from neutron diffraction experiments and from quasi-crystalline models based on the various crystalline polymorphs of GeO 2. The structure is shown to be built of GeO 4 tetrahedra: the coordination number of oxygen about germanium is 4.0 to within one or two per cent, the GeO distance is 1.74 Å and the average GeOGe angle is 133°. The distribution of GeOGe angles is fairly narrow but cannot be determined quantitatively with data of present resolution. The average structure of the glass closely resembles that of the quartz modification as smeared out in the quasi-crystalline model. The remaining differences between model and experiment may be accounted for in terms of an unwinding (and disordering) of the crystal structure by relative rotation of tetrahedra, keeping the average intertetrahedral angle of 133°.