CaO-Y2O3-SiO2 Oxides Prepared at 1700K in Air

Samples having various compositions were prepared in air by solid phase reaction at 1700K in order to investigate the presence of compounds in the CaO-SiO2-Y2O3 system. The quaternary oxides obtained were Ca2Y8Si6O26 (hexagonal, P63/m, a=0.93429 (2), c=0.67393 (1) nm, apatite-type structure), Ca2Y2Si2O9 (monoclinic, P21/c, a=0.74470 (3), b=1.04926 (3), c=1.09666 (5) nm, β=110.179(3)°, cuspidine-type structure), Ca3Y2Si3O12 (orthorhombic, Pnma, a=0.65420(3), b=1.56280 (6), c=1.00331(4)nm, silico-carnotite-type structure) and Ca3Y2Si6O18 (monoclinic, C2/c, a=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 1900K (orthorhombic) and at 1700K (monoclinic). The crystal structure of Ca2Y3Si6O26 was refined by Rietveld analysis for the X-ray powder diffraction pattern.