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

稀土硅酸钙的合成及晶体结构研究

基本信息

批准号：
10450238
负责人：
SHIMADA Masahiko
金额：
$ 8.7万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

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.

本研究采用CaO-Y_2O_3-SiO_2三元体系。在该三元体系中，已经报道了组成为Ca_2Y_8Si_6O_<26>、Ca_3Y_6Si_6O_<24>和Ca_4Y_6Si_6O_<25>的磷灰石型结构化合物。有人指出，磷灰石型化合物的组成尚未确定。对具有尖峰结构的Ca_2Y_2Si_2O_9进行了制备，但晶体学数据尚未见报道。一般来说，硅酸盐有多种同晶型，并形成许多复杂的结构。为此，该多组分体系中有望出现具有新结构的新化合物。在CaO-Y_2O_3-SiO_2三元体系中，通过1700K反应烧结制备的化合物为Ca_2Y_8Si_6O_<26>（磷灰石型结构）、Ca_2Y_2Si_2O_9（尖石型结构）、 Ca_3Y_2Si_3O_<12>(硅碳磷矿型结构)和Ca_3Y_2Si_6O_<18>(新结构)。在Ca_2Y_8Si_6O_<26>中制备具有磷灰石型结构的单相。该相为六方晶系，a=b=0.9341(1)，c=0.6788(1)nm。据报道，成分为Ca_3Y_6Si_6O_<24>的样品为磷灰石型化合物，为Ca_2Y_8Si_6O_<26>和CaSiO_3两相。以Ca_4Y_6Si_6O_<25>组成制备的样品由Ca_2Y_8Si_6O_<26>和Ca_3Y_2Si_3O_<12>组成。 1t证实Ca_2Y_2Si_2O_9具有尖峰型结构(单斜晶系P2_l/c, a=0.74468(3), b=1.049240(3), c= 1.09661 (4)nm, β=110.170(3)゜)。新化合物, Ca_3Y_2Si_3O_<12> 与硅钾镁石 (Ca_5(PO_4)_2SiO_4) 具有同构结构。 Ca_3Y_2Si_3O_<12>为斜方晶系P nma，a=0.65574(2)，b=1.56066(3)，c=1.00399(2)nm。 Ca_3Y_2Si_6O_<18>（单斜晶系C2/c，a=1.33422(5)，b=0.77320(3)，c=1.47959(6)nm，β=90.263(3)゜）由三元SiO_4环组成。