Germanate and Phosphate Glasses

Glassy Ge02 is composed of Ge04 tetrahedra, with a mean Ge-O-Ge bond angle of about 138°. In contrast to fused silica, however, the distribution of inter-tetrahedral angles (Ge-O-Ge) for germanium is quite sharp. 

1 Show that the minimum cation to anion radius ratio for a coordination number of 6 is 0.414. 

2 Calculate the ratio of the sizes of the tetrahedral and octahedral sites. 

3 When oxygen ions are in a hexagonal close-packed arrangement  

1 What is the raho of the octahedral sites to oxygen ions  

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