Planar defects twin boundaries

The introduction to this chapter mentions that crystals often contain extended defects as well as point defects. The simplest linear defect is a dislocation where there is a fault in the arrangement of the atoms in a line through the crystal lattice. There are many different types of planar defects, most of which we are not able to discuss here either for reasons of space or of complexity, such as grain boundaries, which are of more relevance to materials scientists, and chemical twinning, which can contain unit cells mirrored about the twin plane through the crystal. However,... 

The lattice defects are classified as (i) point defects, such as vacancies, interstitial atoms, substitutional impurity atoms, and interstitial impurity atoms, (ii) line defects, such as edge, screw, and mixed dislocations, and (iii) planar defects, such as stacking faults, twin planes, and grain boundaries. 

Another contribution to variations of intrinsic activity is the different number of defects and amount of disorder in the metallic Cu phase. This disorder can manifest itself in the form of lattice strain detectable, for example, by line profile analysis of X-ray diffraction (XRD) peaks [73], 63Cu nuclear magnetic resonance lines [74], or as an increased disorder parameter (Debye-Waller factor) derived from extended X-ray absorption fine structure spectroscopy [75], Strained copper has been shown theoretically [76] and experimentally [77] to have different adsorptive properties compared to unstrained surfaces. Strain (i.e. local variation in the lattice parameter) is known to shift the center of the d-band and alter the interactions of metal surface and absorbate [78]. The origin of strain and defects in Cu/ZnO is probably related to the crystallization of kinetically trapped nonideal Cu in close interfacial contact to the oxide during catalyst activation at mild conditions. A correlation of the concentration of planar defects in the Cu particles with the catalytic activity in methanol synthesis was observed in a series of industrial Cu/Zn0/Al203 catalysts by Kasatkin et al. [57]. Planar defects like stacking faults and twin boundaries can also be observed by HRTEM and are marked with arrows in Figure 5.3.8C [58],... 

Virtually all minerals contain defects. In addition to point defects (e.g., vacancies that exist in a thermodynamically determined equilibrium number, impurities etc ), macroscopic minerals contain line defects (dislocations), and planar defects such as stacking foults, antiphase boundaries and twins. Intergrown layers of different structure or composition, and polytypic disorder also may be present. 

Cation vacancies and interstitials, (111) twins and stacking faults, grain boundaries, microstrains, misfit dislocation network at C03O4/C0O interface Dislocations and (100) stacking faults intergrowth of e and P phases. Cations vacancies and superstructure (110) stacking faults and twins Clusters of point defects (110) twins surface steps, dislocations, spinel microinclusions, planar defects stabilized by impurities. 

Planar defects include grain boundaries, stacking faults, and twins. These defects are formed during ion implantation and thermal and processing. All three types of planar defects are enclosed by a single dislocation or by an array of dislocations separating the faulted area from the normal area or delineating the misorientation between various areas of the semiconductor. 

Figure 1 represents a bright field TEM micrograph of a cross-section of the NiAI/ox-ide interface after the NiAl was oxidized in air at 950 °C for 0.1 h.The oxide scale was observed to be a 40 - 50 nm thick layer all along the NiAl surface. The scale contains many planar defects, possibly twin boundaries. Faceted 200 - 300 nm voids were observed with their facets parallel to (OOl)NiAl and (011 )Ni A1 planes. A thin oxide layer was found at the facetted metal surfaces of some of these voids. 

As for the translation domains of B, they occur because the unit cell of the primitive lattice of B is three times larger than for A, so that each R atom of A can give an Rj or R2 or R3 atom of B, as seen previously. This gives three translation domains, separated by planar defects of translation vectors g[132] and -g[132] which are in this case antiphase boundaries. Each kind of epitaxy of B on A gives 6 x 3 = 18 equivalent domains. When we deal with B regions made of two twinned regions the number of domains is doubled. We can see that the study of the transformation domains is rather complicated for the B structure. It is probably... 

Planar defects are surface imperfections. Examples are the boundaries of separate grains or domains of different orientations— that is, grain and twin boundaries. 

Despite continuing progress in the crystal growth, 3C-SiC films still contain many lattice defects. In particular, twins, stacking faults and antiphase boundaries (APBs) have been reported [64,65]. APBs occur as a common defect when a polar film, SiC in this case, is heteroepitaxially grown on a non-planar substrate. To eliminate this particular defect in 3C-SiC films, Si substrates misoriented from the (100) plane have been used, as stated above [39,53],... 

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