Structure of glasses and elastic constants

Although the origin of low temperature anomaly is unclear, the low pressure anomaly has been attributed to the presence of two different populations of Si-O-Si bond angles. The Si-O-Si bond angle distribution is 

Elastic constants of solids can be related to the fundamental interaction energy terms. In fact it can be shown easily that the bulk modulus, K scales as the energy density, Ulr for an ionic material interacting through Bom-Mayer potential (see later in this section). Thus the molar volume which increases with the presence of larger ions in glasses can be expected to cause a decrease in Young s modulus. 

Theoretical estimates of the Young s modulus were made by Makeshima and Mackenzie (1973) using the formulae 

In the above expression, g. is the energy contribution of component oxide 

The relation between bulk modulus and volume has been widely investigated in both crystalline and glassy systems (Anderson and Soga, 1967 Osaka et al., 1985). From the Bom-Meyer potential, 

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