两种新的SiC高层多型体——417R和453R

本文根据倒易点阵原理,详细分析了碳化硅劳埃照相中各种SiC三方多型体斑点和SiC基本类型6H斑点间的相互配置关系。这种关系共总结出不外乎十二种,本文提出利用这种关系,以及两6H类型斑点(hOl)间未知三方多型体的斑点数目,来计算未知多型体类型层数的方法。利用这一方法,对在实验室条件下以升华法制备的若干碳化硅单晶体进行了分析,发现了两种同时与6H类型连生的新的碳化硅高层多型体417R和453R,其空间群为R3m(C_3v⁵),点阵参数以六方晶胞表示时为 417R:α_H=3.0806?,c=1050.7?,z=417; 453R:α_H=3.0806?,c=1141.4?,z=453。以三方晶胞描述时则为 417R:α_R=350.4?,α=30.4′,z=139; 453R:α_R=380.6?,α=27.8′,z=151。

TWO NEW POLYTYPES OF SILICON CARBIDE 417R AND 453R

A detailed study of the relation between diffraction points of various rhombohedral types and the type 6H of silicon carbide has been made, using the reciprocal lattice method. It was shown that there occur twelve possible relations. A method was proposed for determining the number of the close hexagonal packed layers in unit cell from the relations derived and the numbers of point between two Laue points of the type 6H. By using the method proposed, numerous SiC single crystals prepared in our laboratory were analysed and two new modifications of α-SiC 417R and 453R were found. These two new types are coalescent with the most common type 6H. The space group of the new types is R3m (C_3v⁵). The unit cell dimensions in the hexagonal system for 417R and 453R are as follows respectively: 417R:α_H=3.0806?,c=1050.7?,Z=417; 453R:α_H=3.0806?,c=1141.4?,Z=453 or, in the rhombohedral unit cell: 417R:α_R=350.4?,α=30.4′,Z=139; 453R:α_R=380.6?,α=27.8′,Z=151.