Synthesis and Crystal Structure Characterization of Silicate Apatite Sr_2Y_8(SiO_4)_6O_2

摘要

Pure Sr_2Y_8(SiO_4)_6O_2 powders were obtained after a solid-state reaction at 1400 ℃ for 6 h using the nanosized Y_2O_3, commercial SrCO_3, and silica gel. The nanosized Y_2O_3 powder was synthesized by a precipitation method using Y(NO_3)_3 and NH_4HCO_3, followed by a heat treatment. The crystal structure of Sr_2Y_8(SiO_4)_6O_2 was characterized by powder X-ray diffraction, Rietveld refinement, and high-resolution transmission electron microscopy. Results show that Sr_2Y_8(SiO_4)_6O_2 has a typical apatite-type structure A_4~IA_6~(II)(BO_4)_6X_2 in the P6_3/m space group. The lattice parameters are a - 9.3884(6) A and c = 6.8657(4) A. There are two special sites, A~I (40 and A~(II) (6h), in the apatite structure. The A~(II) sites are fully occupied by Y, while the A~I sites are randomly filled by Y and Sr atoms. The crystallographic data obtained from Sr_2Y_8(SiO_4)_6O_2 and other silicate oxyapatites are compared and summarized.