Points defects

Crystal structure, crystal defects and chemical reactions. Most chemical reactions of interest to materials scientists involve at least one reactant in the solid state examples inelude surfaee oxidation, internal oxidation, the photographie process, electrochemieal reaetions in the solid state. All of these are critieally dependent on crystal defects, point defects in particular, and the thermodynamics of these point defeets, especially in ionic compounds, are far more complex than they are in single-component metals. I have spaee only for a superficial overview. 

The reported shock-modification observations show that shock-treated powders are substantially modified in their defect structures. From the defect point of view they are essentially new materials. Concentrations of point, line, and higher-order defects are found to be as large as those achieved by any... 

The topic of defects in semiconductors encompasses point, line, planar and volume defects. Point defects include those defects occupying, or sharing, a single lattice site these would include substitutional impurities... 

Three-dimensional (volume) defects—point defect clusters, voids, precipitates. 

It is clear that the above mode of computation suffers from the defect pointed out at the start of this section, in the discussion of the force proof of the Young equation (1). If the forces are supposed to cancel each other along a vertical, rather than a horizontal, projection, then the relation obtained... 

In a lattice structure, if the periodicity is locally disturbed, then there is a defect. There are two types of defects point defects and extended defects. A point defect may be any one of the following three types (i) an atom or ion is absent from a site that normally would be occupied (vacancies), (ii) an atom or ion is present in an... 

Non-stoichiometric oxides with high levels of disorder may adopt two modes of stabilization aggregation or elimination of point defects. Point defect aggregates forming clusters are examples of the former and extended defect structures like crystallographic shear-plane structures are examples of the latter. 

Point defects. Point defects (Fig. 5.1) are limited to a single point in the lattice, although the lattice will buckle locally so that the influence of point defects may spread quite far. A Frenkel defect consists of a misplaced interstitial atom and a lattice vacancy (the site the atom should have occupied). For example, silver bromide, which has the NaCl structure, has substantial numbers of Ag+ ions in tetrahedral holes in the ccp Br array, instead of in the expected octahedral holes. Frenkel defects are especially common in salts containing large, polarizable anions like bromide or iodide. 

Point Defects. Point defects are defined as atomic defects. Atomic defects such as metal ions can diffuse through the lattice without involving themselves with lattice atoms or vacancies (Figure 9), in contrast to atomic defects such as self-interstitials. The silicon self-interstitial is a silicon atom that is bonded in a tetrahedral interstitial site. Examples of point defects are shown in Figure 9. 

Crystals contain two major categories of defect point defects and line defects. Point defects occur where atoms are missing (vacancies) or occupy the interstices between normal sites (interstitials) foreign atoms are also point defects. Line defects, or dislocations, are spatially extensive and involve disturbance of the periodicity of the lattice. 

Associated defects Point defects that are associated or clustered are indicated by enclosing the components of such a group in parenthesis. For example, (VmVx) would represent a defect in which two vacancies are associated as a vacancy pair. 

From defectivity point of view, copper CMP is a challenging process because many types of undesirable features could be left on the surface after CMP. Figures 17.22 and 17.23 illustrate some of these possible defects. 

PVC is a vinyl polymer where X is a chlorine atom in the general formula of Scheme 12.3, but its thermal decomposition follows a quite differeut pathway from that of PS, starting with division of the side groups from the main chain. When a chlorine atom is cut off from a defect point (tertiary carbon atom or allyl bond), it abstracts the hydrogen atom from the next carbon atom, then hydrogen chloride is eliminated, together with the... 

Since its formulation, solid state theory has been concerned also with non-strictly-periodic systems, due principally to the theoretical and technological importance of defects (point impurities, color centers, dislocations, surfaces, etc.). However, most of these theoretical studies and approaches exploit the results of the ideal periodic crystal as the basic ingredient on which to include impurity effects. 

There are two types of lattice defects that occur in all real crystals and at very high concentration in irradiated crystals. These are known as point defects and line defects. Point defects occur as the result of displacements of atoms from their normal lattice sites. The displaced atoms usually occupy sites that are not in the lattice framework they are then known as interstitials. The empty lattice site left behind by the interstitial is called a vacancy. Avacancy produced by displacement of an anion or cation, along with its interstitial ion, is called a Frenkel pair, or simply a... 

The singularities in the liquid crystals cause the deformation of the director field of liquid crystals and thus affect the symmetry of liquid crystals. This idea provides an approach to analyze the characteristics of the defects. The order vectors (or scalars, or tensors) of various liquid crystals are not the same. The director n is the order vector of the nematic liquid crystals, but the order for the cholesteric liquid crystals is a symmetric matrix, i.e., a tensor. Because the order vector space is thus a topological one, any configuration of the director field of liquid crystals is thus represented by a point in the order vector space. The order vector space (designated by M) is associated with the symmetry of liquid crystals. The topologically equivalent defects in liquid crystals constitutes the homotopy class. The complete set of homotopy classes constitutes a homotopy group, denoted Hr(M). r is the dimension of the sub-space surrounding a defect, which is related to the dimension of the defect (point, line or wall) d, and the dimension of the liquid crystal sample d by... 

The long and narrow microfibrils are bundled into fibrils their ends, located mainly on the outer surface of fibrils, act as point defects (point vacancies) of the microfibrillar lattice... 

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