Transmission electron microscopy study of optically anisotropic and isotropic haüyne

• Published in: The American mineralogist Vol. 80; no. 1; pp. 87 - 93
• Main Authors: Xu, Huifang, Veblen, David R.
• Format: Journal Article
• Language: English
• Published: Washington Mineralogical Society of America 01.01.1995; Walter de Gruyter GmbH
• Subjects: Crystallography; Crystals; Minerals
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am-1995-1-209

Optically anisotropic and isotropic haiiyne has been observed in phonolite from Niang- niang Hill, Jiangsu Province, southeastern China. Selected-area electron diffraction (SAED) and transmission electron microscopy (TEM) studies show the anisotropic haiiyne has a one-dimensional superstructure with a period of 6d along one of the <110) directions of the ideal cubic haiiyne subcell. The superstructure may be considered as a periodic arrangement of (110) layer domains with P23 symmetry along [110]. Neighboring domains are related by a twin relationship. The unit-cell parameters for this haiiyne superstructure are thus metrically orthorhombic, with a = 2d ,b = 6d , C = c , but the most likely space group is monoclinic, Pn. SAED patterns and TEM images of two opti­cally isotropic haiiyne samples show they have either a three-dimensional superstructure or no superstructure. The average structure of the isotropic haiiyne with the superstructure is cubic, even though it is composed of twin domains with one-, two-, and three-dimen­sional superstructures. The superstructure may have formed by ordering Of[Na Ca(SO )] and [(Na,K) (OH)] clusters in the cubo-octahedral cages of the haüyne framework during an arrested phase transition from P4̄3n to P23 symmetry.