Crystalline perfection

The third law of thermodynamics states that the entropy of any crystalline, perfectly ordered substance must approach zero as the temperature approaches 0 K, and at T = 0 K entropy is exactly zero. Based on this, it is possible to establish a quantitative, absolute entropy scale for any substance as... 

The observed range of the shear modulus varies between 1.5 GPa in filaments of regular count to 3 GPa in microfilaments, which correlates with the degree of orientation and crystalline perfection in the fibres [40]. Compared to the theoretical value of the modulus of shear between two hydrogen-bonded chains of 4.1 GPa, it indicates softening due to the van der Waals bonding between the hydrogen-bonded planes. 

It has also been reasoned that smoothing the crystal surface and improving the chain conformations at the surface could reduce the macroscopic surface free energy and increase the melting temperature without substantially changing the crystalline perfection [82],... 

For metals in general, any mechanical or chemical action that alters the crystalline perfection will raise the residual resistivity and, therefore, the total resistivity, according to Eq. (6.16). Thus, vacancies in metals, in contrast to those in ionic solids, increase the resistivity. The reason for this lies in the inherent differences between condnc-tion mechanisms in these two classes of materials. The differences between ionic and electronic conduction will be elaborated upon in Section 6.1.2. 

The connection between processing conditions and crystalline perfection is incomplete, because the link is missing between microscopic variations in the structure of the crystal and macroscopic processing variables. For example, studies that attempt to link the temperature field with dislocation generation in the crystal assume that defects are created when the stresses due to linear thermoelastic expansion exceed the critically resolved shear stress for a perfect crystal. The status of these analyses and the unanswered questions that must be resolved for the precise coupling of processing and crystal properties are described in a later subsection on the connection between transport processes and defect formation in the crystal.. 

It has been shown that the size and shape of nanostructures plays an essential role in determining the magnetic properties. One critical size of a structure is the SD or MD state. In certain materials the magnetic anisotropy can be influenced by size, shape and configurational anisotropy and in others the crystalline perfection determines the anisotropy. 

An attempt was made in this paper to sketch the behavior of elemental semiconductors (with the diamond-type structure) and of the IH-V compounds (with the zinc blende strut ture) in aqueous solutions. These covalent materials, in contrast to metals, exhibit properties which sharply reflect their crystalline structure. Although they have already contributed heavily to the understanding of surfaces in general, semiconductors with their extremely high purity, crystalline perfection, and well-defined surfaces are the most promising of materials for surface studies in liquid and in gaseous ambients. 

Whisker. Tiny, whisker-like fiber (a few mm long, a few p.m in diameter) that is a single crystal and almost free of dislocations. Note that this term involves a material requirement. The small size and crystalline perfection make whiskers extremely strong, approaching the theoretical strength. 

The large number of applications of the elemental semiconductors silicon and germanium is reflected in the wide range of purity and crystalline perfection over which... 

Figure 4 and 5 and Table III show the DSC data for these RIM specimens. It is seen that AH for the hard segment melting In the unannealed/wlthout PEDA specimens increases on annealing (for both the 18 Eg and 30 Eg series) and essentially the same Increase occurs in the unannealed/with PEDA specimens. These effects corrleate with the X-ray data showing a similar increase in the crystalline perfection of the hard domains with annealing or with the use of PEDA. 

Figure 2.10 Bragg Brentano geometry with a diffracted beam monochromator. The crystal is usually graphite, which has a low degree of crystalline perfection, and hence a large acceptance angle (tenths of a degree). Thus a flat crystal is adequate.

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