1 Technical University of Denmark2 Department of Energy Conversion and Storage, Technical University of Denmark
Orthorhombic α-KFeSi04 ( a =0.5478, b =0.9192, c =0.8580 nm), hexagonal β-KFeSiO4 (a =0.5309, c =0.8873 nm), and hexagonal γ-KFeSi04 (a =0.5319, c =0.8815 nm) were synthesized by devitrification of KFeSiO4 glass. Powder X-ray diffraction data are given for all three polymorphs. Alpha KFeSiO4, the high-temperature polymorph, melts congruently at 1197”±2”C. Mössbauer spectroscopy of the α phase indicates that Fe3+ occupies two tetrahedral sites in the lattice. Beta KFeSiO4, the low-temperature polymorph, and γ-KFeSiO4, a metastable polymorph, appear to be isomorphous with kalsilite, KAISiO4, and synthetic kaliophilite, KAISiO4, respectively, and it is proposed that β- and λ-KFeSiO4 are linked by Si-Fe order-disorder. Beta KFeSiO4 transforms slowly into α-KFeSi04 above 910°C but the transformation was not shown to be reversible in the present dry-heating experiments.
American Ceramic Society. Journal, 1983, Vol 66, Issue 7, p. 475-479