Antiphase domain boundary

A particularly interesting type of transformation twinning has been observed by Reeder and Nakajima (1982) in dolomite the twin boundaries resemble antiphase domain boundaries (see Section 8.8). Modulated structures are also observed in dolomites (van Tendeloo, Wenk, and Gronsky 1985 Wenk, Barber, and Reeder 1983). 

APBs are essentially stacking faults and have been observed by TEM in a number of minerals that undergo order-disorder transformations. Examples include omphacite (Carpenter 1979 Champness 1973 Phakey and Ghose 1973), pigeonite (Bailey et al. 1970 Carpenter 1979 Christie et al. 1971 Fujino, Furo, and Momoi 1988), calcic plagioclase feldspars (Christie et al. 1971 Czank et al. 1973 Czank, Schulz, and Laves 1972 Heuer et al. 1972 McLaren 1973 McLaren and Marshall 1974 Muller et al. 1973 Muller, Wenk, and Thomas 1972 Nord, Heuer, and Lally 1974  

Nord et al. 1973), CaAl2Ge208-feldspar (Muller, Vojdan-Shemshadi, and Pentinghaus 1987), scapolite (Phakey and Ghose 1972), and wenkite (Lee 1976). 

The APBs in anorthite (CaAhSi208) have been studied in considerable detail and are particularly suitable examples to illustrate the principles of the origin of this type of planar defect and the nature of the TEM images. 

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The development of the miscibility gap for W < 0 and the antiphases ( Tjeq) for W > 0 have entirely different kinetic implications. For decomposition, mass flux is necessary for the evolution of two phases with differing compositions. Furthermore, interfaces between these two phases necessarily develop. The evolution of ordered phases from disordered phases (i.e., the onset of nonzero structural order parameters) can occur with no mass flux macroscopic diffusion is not necessary. Because the 77+q-phase is thermodynamically equivalent to the 7/iq-phase, the development of 77+q-phase in one material location is simultaneous with the evolution of r lq-phase at another location. The impingement of these two phases creates an antiphase domain boundary. These interfaces are regions of local heterogeneity and increase the free energy above the homogeneous value given by Eq. 17.14. The kinetic implications of macroscopic diffusion and of the development of interfaces are treated in Chapter 18. 

Long-range order domains may be nucleated at several places within a grain. When the domains grow together, a boundary will be formed if the domains are out of phase. Figure 8.3 illustrated such an antiphase domain boundary. The... 

C.2.1. PdlAl20s Preparation and Structural Properties. To prepare a thin well-ordered AI2O3 model support, a NiAl(l 10) alloy single crystal was oxidized in 10 mbar of O2 at 523 K (290). The structure of the alumina film was examined by a variety of techniques (see Reference (101) and references cited therein), and recently it was even possible to image its atomic structure by STM at 4K (Fig. 19) (215). The alumina film was only approximately 0.5 nm thick and hydroxyl-free, and one should also keep in mind that its exact structure may deviate from those of bulk aluminas (101,215,292,293). Its properties are certainly influenced by the observed line defects (antiphase domain boundaries and reflection domain boundaries). 

Figure 8.27. Diagrams illustrating the formation of an antiphase domain boundary during ordering of a crystal consisting of two types of atom, A and B.

Figure 8.30. Antiphase domain boundaries in synthetic anorthite (Anioo). (a) Difiraction pattern showing sharp a-, b-, c-, and -reflections, (b), (c), and (d) Antiphase domain boundaries imaged in DF with b-, c-, and -reflections, respectively. (From McLaren and Marshall 1974.)...

Figure 8.48. (001) and (100) lamellae (A and B, respectively) of pigeonite in an augite from the Whin Sill, northern England. Between the large (001) lamellae is a tweed structure in which the (001) component is the more prominent. Note the absence of the tweed structure adjacent to the pigeonite lamellae and the antiphase domain boundaries (formed during the C to P transition) in A. 

Muller, W. F., Wenk, H.-R., Bell, W. L., Thomas, G. (1973). Analysis of the displacement vectors of antiphase domain boundaries in anorthites (CaAljSijOj). Contrib. Mineral. Petrol., 40, 63-74. 

Kulawik M, Nihus N, Rust H-P, Freund H-J (2003) Atomic structure of antiphase domain boundaries of a thin Al Oj film on NiAl(llO). Phys Rev Lett 91 256101... 

Barth C, Henry CR (2003). Atomic resolution imaging of the (001) surface of UHV cleaved MgO by dynamic scanning force microscopy. Phys Rev Lett, 91, 196102 Kulawik M, Nihus N, Rust H-P, Freund H-J (2003). Atomic structure of antiphase domain boundaries of a thin Al Oj film on NiAl(l 10). Phys Rev Lett, 91, 256101 20. Kresse G, Schmid M, Napetschnig E, Shishkin M, Kohler L, Varga P (2005). Structure of the ultrathin aluminum oxide film on NiAl(l 10). Science, 308, 1440... 

Fig. 12.4. Schematic illustration of conserved and nonconserved order parameters for characterizing the internal state of a binary alloy (adapted from Chen and Wang (1996)) (a) disordered phase (rj = 0) with uniform composition cq, (b) two-phase mixture consisting of disordered phases (rj = 0) with composition Cq, and c, (c) ordered single phase (ri = 1) of single composition ci with an antiphase domain boundary.

The Portevin-Le Chatelier effect with serrated yielding was observed for both the ordered and disordered state (Mohamed etal., 1974). Recovery and recrystallization have been analyzed in detail (Vidoz etal., 1963 Cahn, 1990, 1991). Experimental and theoretical studies have been directed at dislocations and antiphase domain boundaries (see, e.g. Tichelaar and Schapink, 1991 D. G. Morris, 1992 Veyssiere, 1992), grain boundaries (Yan etal., 1992), and the electronic structure (Bose et al., 1991). It is noted that disordered layers are formed in ordered CujAu on antiphase boundaries and twin boundaries just below the order-disorder transition temperature (Tichelaar et al., 1992). This may be expected in other phases, too, and may improve the ductility of less ductile phases, as is discussed for NijAl (see Sec. 4.1.2). 

Mechanical properties of disordered alloys are also different to those of ordered alloys. This can have a bearing on the techniques used to prepare the alloys. Ordered structures are usually harder than disordered ones. In the former, dislocations have higher energy the Burgers vector is larger because it is defined on the basis of the superlattice. Ako, dislocation movement is hindered by antiphase domain boundaries which may be present in the ordered state. 

It should be noted that the LEED patterns observed for halogen adsorption on the bcc surfaces can also be explained by regularly spaced antiphase domain boundaries [82B]. Such models, however, yield unrealistically small distances between the adsotbed halogen atoms and require complicated concerted motion of the adatoms to obtain continuously varying LEED patterns [82J], Further, electronic band stmcture studies performed on chemisorbed halogen layers on Fe(llO) support the formation of the incommensurate compression phases described above [91M],... 

Rychetsky, I. Deformation of crystal surfaces in ferroelastic materials caused by antiphase domain boundaries. J. Rhys. Condens. Matter 9,4583-4592 (1997)... 

Figure 7.3 Schematic iiiustration of (a) an antiphase domain boundary in a cubic perovskite structure for an ABO3 material, and (b) a ferro-electric domain boundary in a material with a distorted perovskite cell such as BaTi03, which is tetragonal below the Curie temperature. Each sketch shows the projected atomic positions along a viewing direction corresponding to the a-axis, or [100], of the crystal structure. A atoms are dark, B atoms are grey, and oxygen atoms are the large white circles.

Figure 3.4. Structure of adsorbed H formed on Fe(llO) at a coverage 0 = 1/2 below 230 K. The broken line marks an antiphase domain boundary within the adlayer.

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