Structural change by Ca-Sr substitution among 8-coordinated sites in synthetic Sr-Fe³⁺-gehlenite

Abstract

Synthetic [Sr₂Fe³⁺_0.6Al_1.4SiO₇ (SFG)]-[Ca₂Fe³⁺_0.6Al^_1.4SiO₇ (CFG)] series melilites were investigated to reveal the relationship between ionic substitutions at 8-coordinated (W) site and crystal structural change. The results of refinement of crystal structure show that Fe³⁺ is distributed at two tetrahedral sites. The Sr-Ca substitution at the W site causes expansion of WO₈ polyhedra and increase of cell parameters. Due to the T1O₄- and T2O₄-tetrahedra share apexes or edges with WO₈ polyhedra, the tetrahedral sites are influenced by the geometric change of the WO₈ polyhedra.