Dependence of Refractions on the Structure and Thermodynamic Parameters

Ao = 1 if the refraction varies only due to volume change but 1 if the bonding also changes. As shown in Table 11.3, Ao is a sensitive indicator of structural change an increase of in a phase transition decreases the volume more than the refraction. The overestimated Ao of the diamond-graphite pair is an exception, because of aromatic nature of bonding in graphite layers. Polymorphs with the same have refractions identical within ca. 2 % (Table S11.10). 

It is noteworthy that the Muller s factor of a given phase usually remains fairly constant under different thermodynamic conditions, whereas Ao of different substances vary widely, as shown in Table 11.4. For some solids (listed in the left column) the 

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