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A New Three‐Dimensional Superstructure in Bafertisite
Author(s) -
LI Guowu,
XIONG Ming,
SHI Nicheng,
MA Zhesheng
Publication year - 2011
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2011.00538.x
Subject(s) - superstructure , octahedron , monoclinic crystal system , crystallography , supercell , crystal structure , reflection (computer programming) , materials science , chemistry , physics , thunderstorm , meteorology , computer science , programming language , thermodynamics
A new superstructure was found in bafertisite [(Ba 0.98 Na 0.02 ) 1.00 (Fe 1.71 Mn 0.26 Mg 0.01 ) 1.98 TiO [(Si 1.82 Ti 0.04 Al 0.03 Cr 0.01 ) 1.90 O 7 ](OH 1.40 F 0.53 Cl 0.03 ) 1.96 ] from Donghai County, Jiangsu Province, China. The occurrence of the superstructure reflections were observed by single crystal diffraction using a SMAR APEX CCD. The a *, b * and c * axis directions revealed extra weak reflection spots of the superstructure. The apparent 2 a , 2 b and 2 c superstructure is monoclinic with unit cell a = 10.6502(15) Å, b = 13.7233(19)Å, c = 21.6897(3)Å, α= 90°, β= 94.698(3)°, γ=90°, space group Cm, Z = 16. If c * extra weak reflections are ignored, the secondary supercell gave a cell a = 10.6548(15)Å, b =13.7284(19)Å, c = 11.6900(17)Å, α= 90°, β= 112.322(28)°, γ= 90°, space group Cm, Z = 8. The basic subcell was obtained by ignoring all extra weak reflection spots and gave: a = 5.3249(17)Å, b =6.8669(22)Å, c = 10.8709(36) Å, α= 90°, β= 94.740(62)°, γ= 90°, space P 2 1 / m , Z = 2. The superstructure has been refined to R = 0.063 for 7805 [ R (int) = 0.0266] unique reflections I >2δ( I ). The structure consists of an octahedra ( O ) sheet sandwiched between two heteropolyhedral ( H ) sheets. These sheets consist of Ti‐octahedra and twin tetrahedral disilicate groups [Si 2 O 7 ]. The O sheet comprises (Fe,Mg)O 4 octahedra. The large Ba cation is located in the interlayer area. The refined structure shows Fe, Mg are partly ordered. The shifting of the TiO 6 octahedron and SiO 4 tetrahedron sites in the sheet may be a consequence of the superstructure.