Crystal twinning

Synthesis of Pt Tripods and Other Anisotropic Nanocrystals Based on Crystal Twinning... 

Checking the data quality is strongly recommended inspection of the Wilson plot and data reduction statistics is very useful in judging the extent of the resolution to which the data can realistically be used. Pathologically bad data, for example those from a split crystal, twinned data, systematically incomplete data, low resolution overloads will always make model building and refinement hard if not impossible. 

In close-packed stmctures or fee crystals, twinning is introduced by stacking faults. In this case, the excess energy at the twin plane ( = composition plane) is small, and so neither generation nor concentration of dislocations is required. In... 

Figure 10.9. Various forms of rock-crystal twinned according to the Japan law from Narushima Island. Nagasaki Prefecture. Japan. The evolution of crystal forms in the order a->b->c is expected as growth proceeds, due to the re-entrant corner or pseudo re-entrant corner effect.

T. Yasuda and 1. Sunagatva, X-ray topographic study of quartz crystals twinned according to Japan twin law, Phys. Chem. Min., 8,1982,121-7... 

The neutral parent amido species [In(NH2)3] was synthesized by reaction of KNH2 with Ini, in liquid ammonia.Its manner of polymerization in the solid is unknown because diffraction studies were inconclusive as a result of crystal twinning. It was shown to decompose cleanly and quantitatively at moderate temperature to yield InN with liberation... 

FLUORITE. Fluorite is a calcium fluoride mineral CaFi crystallizing in the isometric system, often in superb cubic crystals. Twinned crystals are common, usually as cubic penetration twins. It is found in many diverse... 

Nicol prisms coincide with those of the crystal (ordinary and extraordinary rays) [see Fignre 5.13(c)]. In other positions the color is determined by the birefringence of the crystal, the direction of the light and the thickness of the crystal. This method can be used to determine whether the crystal is single or not, since two or more misaligned crystals (twins) do not extinguish the light completely. 

This is not a method commonly used for coordination compounds, which do not often melt without decomposition. Where applicable, it can be used by cooling from a high-temperature melt to room temperature, or by cooling a room-temperature liquid to a lower temperature. The latter is a specialized technique, usually carried out in situ on a diffractometer, with monitoring of the crystal growth by optical and X-ray methods the sample is contained in a sealed capillary tube, and selective heating may be applied by an infra-red laser to develop a single crystal. Twins and multiple crystals often result from these methods. 

It should be noted that none of the (SN) produced by direct epitaxial polymerization was fibrous in nature as is the conventional material in the normal a form.(7-10) jjot only is the a form produced on KCl not fibrous, it contains none of the extensive crystal twinning observed in the conventional polymerization. Thus greater crystal perfection is obtained by epitaxial pol3oneri-zation. The conventional fibrous a(SN) can be produced if a second deposition of S N is made on produced by... 

Crystal twinning is also relatively easy to produce in these materials. In this process, crystals are formed which consist of two or more regions with the same structure, that is with the same stacking of the molecules, but however different orientations. 

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