Thermodynamic Modeling of the SFCA Phase Ca2(Fe, Ca)6(Fe, Al, Si)6O20

The thermodynamic model of a. silico-ferrites of calcium and aluminum solution, SFCA phase (Ca-2(Fe, Ca)(6)(Oct)(Fe, Al, Si)(6)O-Tet(20)) was newly developed in the framework of the Compound Energy Formalism (CEF). Preferred substitution of Al atoms to tetrahedral sites in the SFCA solution was verified by X-ray absorption near edge structure (XANES) analysis. On considering crystallographic information in particular the short-range-ordering nature in the SFCA solution - the Ca-8(Fe3+)(20)(Oct)(CaSi6+, FeFe6+, FeAl6+)(3)(Paired)(CaSi6+)(1)(Paired)(Fe3+, Al3+)(20)O-Tet(80) structure was considered for modeling the SFCA solution. The optimized Gibbs energies of all end-members can successfully reproduce the experimental single phase region of the SFCA solution.