西藏罗布莎Fe-Cr-Ni合金的X射线晶体学研究

X-ray crystallographic investigation of Fe-Cr-Ni alloy from Luobusa, Tibet

在西藏罗布莎蛇绿岩块的铬铁矿中 ,存在一种Fe -Cr -Ni合金 ,电子探针分析确定其化学分子式为Ni0 .4 5Cr0 .2 9Fe0 .2 6 。其X射线粉晶衍射数据 (括号内为I/Io ,hkl)为 :2 .0 60 (1 0 0 ,1 1 1 )、1 .775(70 ,2 0 0 )、1 .2 61 (60 ,2 2 0 )、1 .0 76(50 ,31 1 )、1 .0 2 7(50 ,2 2 2 ) ,晶体结构应属于金属元素的γ_Fe物相。按其所属空间群金属元素的排列方式 ,确定其原子坐标并计算了理论粉晶衍射图 ,结果表明 ,理论粉晶图谱与实测粉晶衍射数据基本一致。该Fe -Cr -Ni合金晶体学参数可归纳为 :a =3 .562 2 ,空间群Fm3m ,单位晶胞中的分子数Z =4,Dc=8.2 1 2 g/cm3。

A kind of unnamed Fe_Cr_Ni mineral was found in chromite of Luobusa ophiolite in Tibet. EPMA shows that its molecular formula is Ni 0.45 Cr 0.29 Fe 0.26 , and the powder X_ray diffraction data are shown as follows (inside the parentheses are I / I o, hkl ): 2.060 (100, 111), 1.775(70, 200), 1.261(60, 220), 1.076(50, 311), 1.027(50, 222). According to the powder diffraction data, the crystal structure of this alloy belongs to the γ_Fe kind of metal element. The authors determined the atom coordinate and calculated the theoretical powder diffraction pattern in term of the arrangement ways of the metal element. The calculations reveal that the theoretical powder diffraction pattern is basically consistent with the observable powder diffraction data. The crystallographic data of Fe_Cr_Ni alloy can be summed up as follows: a =3.562?2?,space group F m 3 m , the number of molecules in unit cell Z =4, D c=8.212 g/cm 3.