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Twin Interfaces (twin + interface)
Selected AbstractsTwinning and intergrowth of rare earth boride carbidesACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2002Oliver Oeckler Twins and intergrown crystals of tetragonal rare earth boride carbides, especially those with the La5B2C6 structure type, have been investigated by high-resolution electron microscopy and X-ray diffraction. The structure of the twin interface has been determined. It provides an explanation for coherently intergrown domains of different structure. The Sc3C4 structure type is remarkable because it is frequently intergrown with La5B2C6 -type phases. It provides, for instance, a model for the intergrowth of other types, e.g. Gd4B3C4 and Gd5B2C5. The presence of metal-atom square nets in different orientations in the structures accounts for a number of intergrowth phenomena. The possibilities and limitations of X-ray structure determinations are discussed with respect to actual examples. [source] High Pressure Response of Rutile Polymorphs and Its Significance for Indicating the Subduction Depth of Continental CrustACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2008MENG Dawei Abstract: ,-PbO2 -type TiO2 (TiO2 -II) is an important index mineral for ultrahigh-pressure metamorphism. After the discovery of a natural high-pressure phase of titanium oxide with ,-PbO2 -structure in omphacite from coesite-bearing eclogite at Shima in the Dabie Mountains, China, a nano-scale (<2 nm) ,-PbO2 -type TiO2 has been identified through electron diffraction and high-resolution transmission electron microscopy in coesite-bearing jadeite quartzite at Shuanghe in the Dabie Mountains. The crystal structure is orthorhombic with lattice parameters a = 4.58times10,1 nm, b = 5.42times10,1 nm, c = 4.96times10,1 nm and space group Pbcn. The analysis results reveal that rutile {011}R twin interface is a basic structural unit of ,-PbO2 -type TiO2. Nucleation of ,-PbO2 -type TiO2 lamellae is caused by the displacement of one half of the titanium cations within the {011}R twin slab. This displacement reduces the Ti-O-Ti distance and is favored by high pressure. The identification of ,-PbO2 -type TiO2 in coesite-bearing jadeite quartzite from Shuanghe, Dabie Mountains, provides a new and powerful evidence of ultrahigh-pressure metamorphism at 4,7 GPa, 850°C-900°C, and implies a burial of continental crustal rocks to 130,200 kilometers depth or deeper. The ,-PbO2 -type TiO2 may be a useful indicator of the pressure and temperature in the diamond stability field. [source] New approach to twin interfaces of modulated martensiteJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2010Zongbin Li In Ni,Mn,Ga ferromagnetic shape memory alloys, the crystallographic nature of martensitic variant interfaces is one of the key factors governing the variant reorientation through field-induced interface motion and hence the shape memory performance. So far, the crystal structure studies of these materials , conducted by means of transmission electron microscopy , have suffered from uncertainties in determining the number of unit cells of modulated superstructure, and consequently improper interpretations of orientation correlations of martensitic variants. In this paper a new approach is presented for comprehensive analysis of crystallographic and morphological information of modulated martensite, using automated electron backscatter diffraction. As a first attempt, it has been applied for the unambiguous determination of the orientation relationships of adjacent martensitic variants and their twin interface characters in an incommensurate 7M modulated Ni,Mn,Ga alloy, from which a clear and full-featured image of the crystallographic nature of constituent twin interfaces is built up. Certainly, this new approach will make it feasible not only to generalize the statistical analysis of martensitic variant distributions for various materials with modulated superstructure, but also to give insight into the crystallographic characteristics of martensitic variant interfaces and the variant reorientation mechanism of new advanced materials for interface engineering. [source] Structural models for twin interfaces in Pd thin filmsJOURNAL OF MICROSCOPY, Issue 3 2006I. TSIAOUSSIS Summary In a Pd thin film grown on a 6H-SiC (0001) substrate, several twin interfaces have been observed, classified as (1) {111}, = 3 twin interfaces and (2) {}, = 3 twin interfaces. The first ones are coherent twin interfaces and in some cases exhibit steps of one or more atomic layers in height. The second ones are perpendicular to the first ones. They usually appear with a rigid-body displacement, but in some cases no displacement was observed. Models for the interfaces are proposed. [source] | ||||||||||