X-ray study on polymorphism of ilvaite, HCaFe22+Fe3+O2[Si2O7]
X-ray study on polymorphism of ilvaite, HCaFe22+Fe3+O2[Si2O7]
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钛铁矿HCaFe22 Fe3 O2[Si2O7]多晶型的X射线研究
DOI：
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发表时间：
1983
期刊：
影响因子：
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通讯作者：
M. Bunno
中科院分区：
文献类型：
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作者：
Y. Takéuchi;,. N. Haga;M. Bunno
The crystal structure of the monoclinic form of ilvaite has been investigated. A crystal from Tsumo, Japan, was characterized by space group P2Ja, with a = 13.009(1) A, b = 8.8008(3) A, c = 5.8589(2) A, β = 90.324(9)°, whereas a crystal from Techukhe, Siberia, had P2Ja, a = 13.013(3)A, b = 8.8197(6)Â, c = 5.8424(5) Α, β = 90.03(1)°. In the structure, the octahedra formed by oxygen atoms about Fe(ll) and those about Fe(12) are alternately linked together, sharing edges to form a chain of octahedra parallel to c. The monoclinic symmetry of ilvaite is characterized by ordering of Fe + and Fe + which are distributed over these two Fe sites with a ratio of 1:1. The atomic contents in the Fe(ll) site, estimated from mean F e ( l l ) 0 length, are: Tsumo ilvaite 0.85Fe and 0.15Fe, and Techukhe ilvaite 0.53 Fe + and 0.47 Fe + . From these atomic occupancies, the order parameter, σ, of Tsumo ilvaite is calculated to be 75 %, while that of Techukhe ilvaite 6 %. From the two cases of monoclinic ilvaites, a relation between β and a has been deduced; the result permits predicting β » 90.45° for an ilvaite crystal having σ = 100 %. The orthorhombic form of ilvaite may be defined as a form of ilvaite having σ = 0.
