Atomic ordering in glasses (x=0,0.34,0.5,0.68) by energy-dispersive x-ray diffraction

Extended structure factors for (Formula presented) glasses (x=0,0.34,0.5,0.68) have been obtained by energy-dispersive x-ray diffraction. The first neighbor Si-O and Al-O interatomic distances and coordination numbers have been determined thanks to the improved resolution of the experimental atomic distribution functions. It has been found that Al atoms are always fourfold coordinated by oxygen atoms while the oxygen coordination of Si atoms varies with the change of Al and Ca contents in the glasses investigated. The experimental information obtained has made it possible to discriminate between contradicting structure models for (Formula presented) glasses (x=0,0.34,0.5,0.68) that have been previously proposed.