Disilicates binary

Sc + and In3+, which are even smaller than Lu +. The reason for the extensive stability area of this thortveitite structure (see also Fig. 42) might be seen in the almost closest packing of the oxygens with the silicons emd rare earths on the tetrahedral and octahedral sites respectively. On the other hand, the smaller stability range of the larger rare-earth disilicate structures is best demonstrated by the large variance in coordination numbers and in RE—O distances found in the individual coordination shells. This is also shown by the data of. e.g. PrDi A. as compared to Yb Di C in Table 22. Tables 22 and 23 present the coordination data on (RE—0 )polyhedra and (Si04)tetrahedra of the individual structures. Structural data of compounds other than the binary compounds have not been taken into consideration because of their relatively poor accuracy. 

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