Twin formation

Watari, F. Delavignette, P. Van Landuyt, J. Amelinckx, S. (1979) Electron microscopic study of dehydration transformations. I. Twin formation and mosaic structure in hematite derived from goefhite. J. Solid State Chem. 

In general, a low-temperature polymorph has lower symmetry than a high-temperature polymorph. So, in the phase transformation from high- to low-temperature polymorph, the low-temperature polymorph can have two orientations, which leads to twin formation. This is called the transformation twin. To minimize the interface energy between twinned individuals through transfer-... 

I. Sunagawa, Mechanism of crystal growth, etching and twin formation of hematite. Mineral. J 3,1960, 50-89... 

The T(ioo twin structure was also studied in Ref [99]. The pyramidal structures, often seen on the (100) faces of HOD films, were identified as penetrating twins, as shown in Figure 6.4 (a). The (111) face of the pyramidal structure tilted by 15.8° with respect to the basal (100) face, and the [221] direction of the twin is parallel to the [100] direction of the basal (100) face. It was inferred that the atomic arrangement of carbon at the beginning of the penetrating twin formation looks like the one shown in Figure 6.4 (b), which is seen from the [110] direction of the basal (100) face. 

Fig. 5.4. Model of parallel-twin formation during crystal growth from Si melt. The growth interface is faceted as shown in (a), when a twin boundary is accidentally formed on a 111 facet face, another twin boundary is formed parallel to the first twin after lateral growth is promoted (from (b) to (d)). The direction of growth of the faceted dendrite should be parallel to the 111 facet plane in this model [16]...

C. Wild, R. Kohl, N. Hetres, W. Miiller-Sebert, and P. Koidl, Oriented CVD diamond films twin formation, structure and morphology. DiamondRelat Mater., 3 373-381 (1994)... 

Compared with rutile, the anatase crystals were found to be very large (10 pm). Anatase twin formation was also observed [23]. When evaporating 2 (anatase) onto sodium chloride cleavage surfaces, amorphous films are obtained which also crystallize into rutile and anatase under strong electron radiation [24, 25]. 

Samples of quartz crystals were crushed into micron size particles using vibro-set with W-carbid. They did not indicate the condition of the pounding of the crystals although it is well known that crushing of the optically active quartz particularly with vibro-mil can cause twinnings formation, amorphisation of quartz, and its hydrophilisation... 

We shall study the following topics twinning elements, mechanical twin formation, twin junction and twin intersection, twin by crystal growth and grain boundaries, the real structure of B, and A, B phase transformation and the domains of B by phase transformation. 

In this section, the formation of deformation and annealing twins were discussed with the resulting stress-strain relation characterized by serrated curves. As indicated here, there is no basic difference in twin formation between ceramics and metals. 

Other transformations, such as ferroelastic transformation and twin formation in a system may also induce toughening effects. The former discussion on stress-induced transformation was Martensitic, involving both dilation and shear components of the transformation strain. Twin transformation typically only has a... 

The destruction of monocrystalline epitaxial growth occurs by accumulation of crystal defects as dislocations and than twin formation (Fig.6). 

Twin formation due to tetra-ortho transition at low depends on growth regime. 

Kutami, H., Y. Yamada, S. Koyama, Z. Nakagawa and Y. Shiohara, 1997, Preparation of twin-free YBajCujO, i, crystal without twin formation, in Proc. ISS 96, Sapporo, Japan, eds S. Nakajima and M. Murakami, Vol. IX of Advances in Superconduetivity (Springer, Tokyo) pp. 689-692. 

The improved pitting potential at low deformation rates i.e. below 20 % is due to the decreased tendency for twin formation. At higher deformation rates, deformation bands will appear which will be influenced by nitrogen (width and dislocation configuration). [Pleva, 1991] reports that the degree of cold working does not show any influence on the pitting corrosion. This has been also confirmed by own data on XSCrMnN 18-18 material, see fig.20 21 [ETE-11]. 

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