CaO-Y₂O₃-SiO₂ oxides prepared at 1700 K in air

Samples having various compositions were prepared in air by solid phase reaction at 1700 K in order to investigate the presence of compounds in the CaO-SiO₂-Y₂O₃ system. The quaternary oxides obtained were Ca₂Y₈Si₆O₂₆ (hexagonal, P6₃/m, α=0.93429(2), c=0.67893(1)nm, apatite-type structure), Ca₂Y₂Si₂O₉ (monoclinic, P2₁/c, α=0.74470(3), b=1.04926(3), c=1.09666(5)nm, β=110.179(3)°, cuspidine-type structure), Ca₃Y₂Si₃O₁₂ (orthorhombic, Pnma, α=0.65420(3), b=1.56280(6), c=1.00331(4)nm, silico-carnotite-type structure) and Ca₃Y₂Si₆O₁₈ (monoclinic, C2/c, α=1.33422(5), b=0.77320(3), c=1.47959(6)nm, β=90.263(3)°). Reversible phase transformation of Ca₂Y₂Si₂O₉ was suggested from the examination of samples annealed at 1900 K (orthorhombic) and at 1700 K (monoclinic). The crystal structure of Ca₂Y₈Si₆O₂₆ was refined by Rietveld analysis for the X-ray powder diffraction pattern.