Crystals perfection

Due to the very fast processes in precipitations, the crystal perfection can deteriorate considerably. This can be seen, for example, in a peak broadening in the XRPD diffractogram. However, a peak broadening is also to be expected for small crystal sizes. 

It should be stressed that the conditions for precipitation can only influence the size of the primary particles. The size of the agglomerates will mainly depend on other conditions of the process, such as the shear field generated by mixing. 

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Ingots of EGS are evaluated for resistivity, crystal perfection, and mechanical and physical properties, such as she and mass. The iagots are sHced iato wafers usiag at least 10 machining and polishing procedures. These wafers are sHced sequentially from the iugot, and evaluated for the correct surface orientation, thickness, taper, and bow. As a final procedure, the wafers are chemically cleaned to remove surface contaminants prior to use. 

Clay particles are so finely divided that clay properties are often controlled by the surface properties of the minerals rather than by bulk chemical composition. Particle size, size distribution, and shape the nature and amount of both mineral and organic impurities soluble materials, nature, and amount of exchangeable ions and degree of crystal perfection are all known to affect the properties of clays profoundly. 

It is no exaggeration to claim that it was the extensive worldwide body of research on semiconductors from the late 1930s onwards that converted physicists to the recognition that scrupulous control of purity, stoichiometry and crystal perfection, together with characterisation methods that could check on these features, are a precondition of understanding the nature of semiconductors and thus also a precondition of exploiting them successfully - indeed, not only semiconductors but, by extension, many kinds of materials. 

B GO Solid Amorphous solid Real crystal Perfect crystal... 

Fontaine et al. [81] concluded that the increase in crystallinity by further heating material, crystallized at 200 °C, to 215 °C involves a crystal (lamellae) thickening process which is probably due to crystal perfection at the boundary layers. Further annealing of this material at temperatures above 215 °C led to a melting temperature increase that was attributed to crystal perfection alone and not to crystal thickening. 

Alfonso, G. C., Pedemonte, E. and Ponzetti, L Mechanism of densifica-tion and crystal perfection of poly(ethylene terephthalate), Polymer, 20, 104-111 (1979). 

Fontaine, F., Ledent, J., Groeninckx, G. and Reynaers, H Morphology and melting behaviour of semi-crystalline poly(ethylene terephthalate) 3. Quantification of crystal perfection and crystallinity, Polymer, 23,185-191 (1982). 

The instmment shown in Figure 2.4 is a double-axis instrument. The first axis is the adjustment of the beam conditioner, the second is the scan of the specimen through the Bragg angle. It is irrelevant to this definition that a practical diffractometer may contain a dozen or more controlled axes , for example, to tune and to align the beam conditioner, to locate the specimen in the beam, to align and to scan the specimen and to control shts. It is the differential movement of the two main axes that make the measnrement and determine the precision and accuracy of the instrument. This is the basic high resolntion diffractometer, which is now widely nsed for measniements of crystal perfection, epilayer composition and thickness. 

Double-axis topography can be used at the two extremes of crystal perfection. On the one hand it can be used to probe the long-range lattice strains in very highly perfect crystals. On the other, it can be used to reveal contours of equal misorientation in much less perfect materials. As we will see in Chapter 10, it is widely used at synchrotron radiation sources and with the very large power loading in the white beam of third-generation synchrotron radiation sources. It is... 

Graphite is midway between a semiconductor and a metal in electrical characteristics. The resistivity is very sensitive to impurities, and therefore to crystal perfection, and is directional, being two to three times greater in the basal plane than perpendicular to the plane. Properties measured in the hexagonal plane are independent of the direction within the plane, probably... 

Note Recrystallization is likely to result in an increase in the degree of crystallinity, or crystal perfection, or both. 

Furthermore, it can be fabricated very easily as a thin film by a technology that not only inherently escapes the expense of crystal perfection but also requires significantly smaller amounts of raw materials. 

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