有序绿辉石空间群类型的群论研究

本文根据畴结构的群论原理,对有序绿辉石的空间群归属问题(P2还是P2/n)进行了讨论。通过把无序绿辉石的空间群C2/c分别相对于P2和P2/n的陪集展开可以得知,C2/c→P2相变将产生■的反相畴及■(001/2)和(■1/2 1/2 1/2)两种倒反孪晶,而C2/c→P2/n相变则仅产生■/2的反相畴,显然后者与有序绿辉石畴结构的透射电境观察结果一致。因此可以断定,有序绿辉石的空间群为P2/n,而非P2。

A GROUP-THEORETICAL STUDY ON THE TYPE OF SPACE GROUP OF ORDERED OMPHAClTE

Based on the group theory of domain structure, the problem that the type of space group of ordered omphacite is P2 or P2/n has been discussed. By decomposing C2/c, the space group of disordered omphacite, with respect to P2 and P2/n, respectively, we deduced that the transformation of C2/c into P2 results in the antiphase domain boundaries with a displacement vector of (a + b )/2 as well as two kinds of inverslon-twin boundaries with the boundary operators of(|001/2)and(|1/2 1/2 1/2), but the transformation of C2/c into P2/n only results in the antiphase domain boundaries. Obviously, the latter is coincident with the TEM observational result of domain structure of ordered omphacite. Hence, it is concluded that the space group of ordered omphacite is P2/n, not P2.