Study on Synthesis and Crystal Structure of Rare-Earth Calcium Silicate

In the present study, ao_y_2_3 - sio_2 ternary system was taken up. In this ternary system，apatite-type structure compounds have been reported at the compositions of ca_2 y_8 si_6o_ <26>，ca_3 y_6 si_6o_ <24> and ca_4 y_6 si_6o_ <25>. It was pointed out that the composition of apatite-typecompounds had not been established. The preparation of ca_2y_2 si_2o_9 having a cuspidine-typestructure was carried out，但crystallographic数据未被预先报告。silicates have many isomorphs and form many complicated structures For this reason，new compounds having new structure are expected in this multicomponent system.In cao - y_2_3 - sio_2ternary system,the compounds prepared by reaction sintering at 1700K were ca_2 y_8 si_6o_ <26> （apatite-type）structure), ca_2 y_2 si_2o (cuspidine-type structure)，ca_3 y_2 si_3o_ <12> (silico-carnotite-type structure) and ca_3 y_2 si_6o_ <18> (new structure).Asingle-phase having an apatite-type structure was prepared at ca_2 y_8 si_6o_ <26>. This phase ishexagonal, a = b = 0.9341 (1),c=0.6788(1)nm. The sample with The composition of ca_3y_6si_6o_ <24> which was reported asapatite-type compound was two phases，ca_2 y_8 si_6o_ <26> and casio_3 . The sample prepared at The composition of ca_4 y_6 si_6o_ <25> consistedof ca_2 y_8 si_6o_ <26> and ca_3 y_2 si_3o_ <12>. 1t was confirmed that ca_2 y_2 si_2o_9 had acuspidine-type结构(monoclinic p2_l /c, a=0.74468(3), b=1.049240(3), c= 1.09661 (4)nm，β=110.170(3) .The new compound，ca_3 y_2 si_3o_ <12> is isostructual with silico-carnotite (ca_5 (po_4)_2 sio_4). ca_3 y_2 si_3o_ <12> isorthorhombic P nma, a=0.65574(2), b=1.56066(3), c=1.00399(2)nm. ca_3 y_2 si_6o_ <18> (monoclinic C2/c，a=1.33422(5), b=0.77320(3), c=1.47959(6)nm, β=90.263(3)) is composed of ternary sio_4 rings。

In the present study, CaO-Y_2O_3-SiO_2 ternary system was taken up. In this ternary system, apatite-type structure compounds have been reported at the compositions of Ca_2Y_8Si_6O_<26>, Ca_3Y_6Si_6O_<24> and Ca_4Y_6Si_6O_<25>. It was pointed out that the composition of apatite-type compounds had not been established. The preparation of Ca_2Y_2Si_2O_9 having a cuspidine-type structure was carried out, but the crystallographic data has not been reported yet. Generally, silicates have many isomorphs and form many complicated structures. For this reason, new compounds having new structure are expected in this multicomponent system.In CaO-Y_2O_3-SiO_2 ternary system, the compounds prepared by reaction sintering at 1700K were Ca_2Y_8Si_6O_<26> (apatite-type structure), Ca_2Y_2Si_2O_9 (cuspidine-type structure), Ca_3Y_2Si_3O_<12> (silico-carnotite-type structure) and Ca_3Y_2Si_6O_<18> (new structure).A single-phase having an apatite-type structure was prepared at Ca_2Y_8Si_6O_<26>. This phase is hexagonal, a=b=0.9341(1), c=0.6788(1)nm. The sample with the composition of Ca_3Y_6Si_6O_<24> which was reported as apatite-type compound was two phases, Ca_2Y_8Si_6O_<26> and CaSiO_3. The sample prepared at the composition of Ca_4Y_6Si_6O_<25> consisted of Ca_2Y_8Si_6O_<26> and Ca_3Y_2Si_3O_<12>. 1t was confirmed that Ca_2Y_2Si_2O_9 had a cuspidine-type structure (monoclinic P2_l/c, a=0.74468(3), b=1.049240(3), c= 1.09661 (4)nm, β=110.170(3)゜).The new compound, Ca_3Y_2Si_3O_<12> is isostructual with silico-carnotite (Ca_5(PO_4)_2SiO_4). Ca_3Y_2Si_3O_<12> is orthorhombic P nma, a=0.65574(2), b=1.56066(3), c=1.00399(2)nm. Ca_3Y_2Si_6O_<18> (monoclinic C2/c, a=1.33422(5), b=0.77320(3), c=1.47959(6)nm, β=90.263(3)゜) is composed of ternary SiO_4 rings.