论文部分内容阅读
桐柏矿(Cr3C2)是我国1983年发现的新矿物,因当时实验条件所限仅进行了晶体学参数测定而未进行晶体结构测定。最近在西藏罗布莎蛇绿岩块铬铁矿矿床中又一次发现该矿物,并获得了适宜进行X射线单晶衍射分析的单晶颗粒。采用SMARTAPEX单晶衍射仪电子耦合探测器技术,对该矿物进行了晶体结构的精确测定。测得该矿物属斜方晶系,空间群为Pnam,晶胞参数为a=0.5525(2)nm,b=1.1468(4)nm,c=0.2827(1)nm,晶胞体积V=0.1791(1)nm3,得到了精确的Cr和C原子坐标及其它晶体学参数,单位晶胞内分子个数Z=4{Cr3C2},计算密度D=6.677g/cm3,结构测定精度R(I>2σ(I))=0.0361。测定表明,该矿物属过渡金属碳化物结构,金属原子Cr与C原子呈非等大球的密堆积,C原子与最近邻的6个Cr原子配位,呈三方柱配位多面体,三方柱之间以共棱和共面方式连接。两种[CCr6]三方柱中,Cr—C平均键长分别为0.2047nm及0.2083nm。本文对该矿物与其它类似的过渡金属元素碳化物的晶体结构进行了对比研究。
Tongbai Mine (Cr3C2) is a new mineral discovered in China in 1983, due to the experimental conditions at the time only the determination of crystallographic parameters without the determination of the crystal structure. The mineral was found again recently in the Luobusa ophiolite block chromite deposit in Tibet and single crystal particles suitable for X-ray single crystal diffraction analysis were obtained. Using SMARTAPEX single crystal diffraction electron coupling detector technology, the mineral crystal structure was accurately measured. The mineral is orthorhombic and the space group is Pnam. The unit cell parameters are a = 0.5525 (2) nm, b = 1.1468 (4) nm, c = 0.2827 (1) nm and unit cell volume V = 0.1791 1) nm3, accurate Cr and C atomic coordinates and other crystallographic parameters were obtained. The number of molecules per unit cell was Z = 4 {Cr3C2}, the calculated density was D = 6.677g / cm3, and the structure determination accuracy was R (I> 2σ (I)) = 0.0361. The results show that the mineral is a transition metal carbide structure, the metal atoms Cr and C atoms are non-large ball closely packed, C atoms and the nearest neighbor of the 6 Cr atoms coordination, was a tripartite column coordination polyhedron, Co-prism and coplanar way to connect. Among the two [CCr6] tripartite columns, the average bond length of Cr-C was 0.2047 nm and 0.2083 nm, respectively. In this paper, the crystal structures of the minerals and other similar transition metal carbides are compared.