Coordination of the Network Cations

The coordination numbers of all cations which occupy sites in the vitreous network, i.e., the building blocks which constitute the network, provide the most basic element of any model for glass structures. Since these building blocks are usually well defined structures such as tetrahe-dra or triangles, they exhibit order at the level of several associated atoms or ions. Since this order only extends over a very short distance, it is termed short range order. 

It follows that the starting point for any model for the structure of a vitreous material must lie in a determination of the coordination unit for the high field strength cations, which serve as the network forming cations in the material. Traditionally, we estimate the possible coordination number of each cation using the radius ratio, or by consideration of the coordination states usually observed for these cations in other materials. On this basis, we can state that silicon is almost 

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Network connectivity, however, should not be considered solely in terms of NBO concentrations. The coordination of the network cations is also an important factor in determining the connectivity of the... 

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