Crystal Structure of Natural Non-metamict Ti- and Fe2+-rich Chevkinite-(Ce)
The crystal structure of non-metamict Ti- and Fe2+-rich chevkinite-(Ce) has been redetermined with the single-crystal sample colleeted from Bayan Obo, Inner Mongolia,China The chemical formula of the sample is Ce4Fe2Ti3Si4O22. The crystals are monoclinic with the unit cell parameters a= 13.4656(15) A;b=5:7356(6)A,c =11.0977(12) A, β= 100 636(2)° V = 842.39 (16) A3 and Z =2.The structures of Ti- and Fe2+-rich chevkinite-(Ce)were refined with space groups P2/a and C2/m. Least-squares refirement results show that both structural models of Ti- and Fe2+- rich chevkinite-(Ce) are very good, R[F2＞2σ(F2)] =0.027 with P21/a and R[F2＞2σ(F2)] =0.021 with C2/m In order to illustrate the relationship between the two space groups P21/a and C2/m,the distribution of diffraction intensities was inspected. Pseudo extinction was found,i.e., reflections with h+k=2n are systematically strong,while those with h+k=2n+ 1 are weak. By neglecting the systematically weak (h+k=2n+1)reflections the space groupbecomesC2/m.There is a mirror plane in the C2/m perpendicular to the b axis However, oxygen atoms in the P21/a model are of a symmetrical relationship with the corresponding pseudo mirror plane It is concluded that the crystal structure of non metamict Ti-and Fe2+-rich chevkinite-(Ce) is a superstructure with the space group of P21/a, which is of pseudo symmetrv coprresponding to the space group C2/m.
作 者： LI Guowu YANG Guangming Ma Zhengsheng Shi Nicheng XIONG Ming FAN Haifu SHENG Ganfu 作者单位： LI Guowu,Ma Zhengsheng,Shi Nicheng,XIONG Ming(China University of Geosciences (Beijing),Beijing 100083)YANG Guangming(China University of Geosciences (Wuhan),Wuhan,Hubei 430074)
FAN Haifu(Institute of Physics,Chinese Academy of Sciences,Beijing 100080)
SHENG Ganfu(Chenodu Institute of Geolooy and Mineral Resources,Chenodu,Sichuan 610082)
刊 名： 地质学报（英文版） SCI 英文刊名： ACTA GEOLOGICA SINICA 年，卷(期)： 2005 79(3) 分类号： P5 关键词： non-metamict Ti- and Fe2+-rich chevkinite-(C e) crystal structure space group sup erstructure