Atomic order

The arrangement of crystallites in the cross-section of carbon fibers is complex and is affected by the precursor type and stmcture, fiber spinning conditions. 

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Some materials that are atomically ordered also develop a sHp-iaduced anisotropy as a result of plastic deformation. The origin is thought to be identical to that of thermomagnetic anisotropy, ie, short-range directional order, except that the order is brought on by deformation rather than by heat treatment ia a field (3,4). 

Cahn, R.W. (1994) The place of atomic order in the physics of solids and in metallurgy, in Physics of New Materials, ed. Fujita, F.E. (Springer, Berlin) p. 179. (1998) Second, updated edition. 

Transmission electron microscopes (TEM) with their variants (scanning transmission microscopes, analytical microscopes, high-resolution microscopes, high-voltage microscopes) are now crucial tools in the study of materials crystal defects of all kinds, radiation damage, ofif-stoichiometric compounds, features of atomic order, polyphase microstructures, stages in phase transformations, orientation relationships between phases, recrystallisation, local textures, compositions of phases... there is no end to the features that are today studied by TEM. Newbury and Williams (2000) have surveyed the place of the electron microscope as the materials characterisation tool of the millennium . 

Amorphous alloys stable at ambient and higher temperatures consist of at least two components without any long-range atomic order. They are produced by a variety of constituents from the gas, liquid and aqueous phases. Vitrification of metal surfaces is also caused by destruction of the long-range atomic order in the surfaces of solid metals. 

Phase transition occurs at a state of thermodynamic equilibrium, inducing a change in the microstructure of atoms. However, corrosion is a typical nonequilibrium phenomenon accompanied by diffusion and reaction processes. We can also observe that this phenomenon is characterized by much larger scales of length than an atomic order (i.e., masses of a lot of atoms), which is obvious if we can see the morphological change in the pitted surface. 

The measured growth rates are illustrated by the circles in Fig. 7. The interface velocity is plotted versus the interface temperature T. The value of T is always greater than Tq because of the release of the latent heat at the interface. Dimensionless units for T and the velocity are used here. The maximum velocity corresponds to 80m /s for argon. The most surprising aspect is the rapid crystallization at low temperatures. Most materials exhibit sharply reduced rates at low temperatures, as expected for an activated growth process. That is, the kinetics can be represented as the product of an Arrhenius factor F(T) and a term that accounts for the net production of crystalline material as a result of the atoms ordering and disordering at the interface,... 

We note that the valence orbitals of metal atoms order in energy as AE>Ln>M. The d-levels of transition elements (M) range the lowest, and are therefore most sensitive for reduction, or to form a stable binary metal nitride. This may also explain the virtual absence of d-element compounds with 16 (valence) electron species, such as [N=N=N] , [N=C=N] , [N=B=N] T [C=C=CfT or [C=B=C] T at least through high-temperature syntheses. 

Because a regular triacontahedron can be geometrically decomposed into ten prolate and ten oblate rhombohedra, the 1/1 and 2/1 ACs can also be viewed as two different types of periodic condensations of prolate and oblate rhombohedral building blocks. In this way, a link between AC structures and 3D Penrose tiles [93] used for i-QC modeling becomes evident. Therefore, the local atomic orders within and the linkages among triacontahedra are very useful in QC modeling. 

For energetic reasons, internal boundaries are almost always planar in crystals. This is not a mle, though, and in some circumstances curved boundaries can occur. These are frequently found when the boundary is simply a variation in metal atom ordering of the type characterized by antiphase boundaries (see below). 

A similar development in this direction is the synthesis of a mixed-phase material containing both micro- and mesopores (Ti-MMM-1) (223). This material was synthesized by the addition of organic templates for mesopores (cetyltrimethylammonium bromide, CTABr) and micropores (tetrapropylammo-nium bromide, TPABr) at staggered times and the variation of the temperature of a single reaction mixture. Ti-MMM-1 is more selective (for oxidation of cyclohexane and of n-octane) than either Ti-MCM-41 or TS-1. The powder X-ray diffraction pattern indicates that the material contains both MCM-41 and MFI structures. The mixed phase contains framework Ti species and more atomic order within its walls than Ti-doped MCM-41. 

This shape of the powder pattern is that predicted (5) for an 7 = nucleus in axial symmetry. This situation occurs for the Al nuclei in a-AljOs which is a hexagonal close-packed array of oxygen atoms with the aluminum atoms ordered in of the holes octahedrally coordinated with oxygen atoms. 

Low energy electron diffraction (LEEDS) Structure/long range atomic order Electrons in, electrons out... 

Thermal diffusion in petrology. In Diffusion, Atomic Ordering, and Mass... 

Morioka M. and Nagasawa H. (1991) Ionic diffusion in olivine. In Diffusion, Atomic Ordering, and Mass Transport (ed. J. Ganguly), pp. 176-197. New York Springer-Verlag. 

In summary, the superconducting compositions appear to have a tetragonal structure for BaPbj Bi Og, and a cubic structure for Ba K BiOg. Dopant atom ordering has not been reported in structural studies. 

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