Crystal structure cubic, orthorhombic and monoclinic modifications

1 Crystal structure cubic, orthorhombic and monoclinic modifications 

A can incorporate Na by substitution of Ca with inclusion of a second Na ion in an otherwise vacant site, thus giving solid solutions of general formula Na2vCa3 j,.Al20 (F2,R5,R1,T4). The substitution occurs without change in structure up to a limit of about 1% Na O (.v 0.04). 

Higher degrees of substitution lead to a series of variants of the structure (Table 1.6). In the absence of other substituents, the upper limit of Na,0 substitution is 5.7%. 

Approximate Na,0 (%) Compositional range -V Designation Crystal system Space group 

Substantial proportions of the aluminium in these structures can be replaced by other ions, of which Fe and Si are the most important. Lee et al. (LI) found the limits of substitution under equilibrium conditions to be 

---