MEDIUM-RANGE ORDER IN V-SIO2

A computer algorithm has been developed to generate fully valence-satisfied models of amorphous AX2 chemically ordered continuous random networks. The specific application here is the successive addition of rigid corner-sharing AX4 tetrahedral units and the networks produced are analyzed with reference to the structure of v-SiO2. Control over parameters such as bond angles, minimum ring size and dihedral angle is possible while short-range order is ensured by using rigid AX4 tetrahedral units as the basic building block. Models have been generated to investigate a region of parameter space with minimum ring size and equilibrium SiOSi bond angles as variables. Careful considerations is given to the effects of experimental resolution, thermal broadening and finite model-size correction when comparing the models with experimental data. It is found that a comparatively narrow region of parameter space gives rise to good models assessed in terms of their fit to experimentally derived real-space distribution functions, bond-angle distributions, reciprocal space scattering data and, in particular, the relative intensity of the first sharp diffraction peak (FSDP). © 1990.