Defects ordered

Conventional physical descriptions of materials in the solid state are concerned with solids in which properties are controlled or substantially influenced by the crystal lattice. When defects are treated in typical solid state studies, they are considered to modify and cause local perturbations to bonding controlled by lattice properties. In these cases, defect concentrations are typically low and usually characterized as either point, linear, or higher-order defects, which are seldom encountered together. 

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... 

Carr and his co-workers [86C01, 87C01] have shown that transmission electron microscopy is a powerful tool in characterizing linear and higher-order defect configurations and their densities on shock-modified rutile, alumina, aluminum nitride, and zirconia [84H02]. The principal impediment to detailed characterization of shock-formed defects is their very high concentrations, which prevent identification of specific deformation features except in... 

Ga-Ga bonds Ga4S5 a-Ga2S3 (yellow) ordered defect (Ga3Tc2)... 

In2S3 (red) defect spinel, /9-In2Se3 ordered defect wurtzite /9-In2Te3... 

Continued reduction causes an increase in the density of the CS planes and as the composition approaches WO2.97, they tend to become ordered. In the case where the CS planes are perfectly ordered, defects are no longer present. Each CS plane is equivalent to the removal of a 102 oxygen-only plane, and the composition of a... 

However, a detailed model for the defect structure is probably considerably more complex than that predicted by the ideal, dilute solution model. For higher-defect concentration (e.g., more than 1%) the defect structure would involve association of defects with formation of defect complexes and clusters and formation of shear structures or microdomains with ordered defect. The thermodynamics, defect structure, and charge transfer in doped LaCo03 have been reviewed recently [84],... 

In precipitation studies (4 7, 4 ) it has been shown that, below a certain Mg/Ca concentration ratio in the aqueous solution, the rate of nucleation of calcite was faster than that of aragonite. Above that Mg/Ca ratio the order was reversed. This was explained by the effect of Mg2+ ions on the interfacial tension between the solution and precipitate, which apparently is larger for calcite than for aragonite (49). At still higher Mg/Ca ratios dolomite can be formed (50). Such low temperature precipitates of dolomite contain ordering defects. The number of defects increases when precipitation proceeds in a shorter time interval or at lower temperatures C51 ). 

The picture just outlined for a-Na3Hg (Na3As type) can be transferred to / -Na3Hg (Li3Bi type) and to the three modifications of NasHg3 which crystallize in an ordered defect variant of an A3B structure [4]. 

Figure 5.12 (a) Ordered defects in monoclinic TiOfTij gOj g) (b) ordered defects in (orthorhombic) nonstoichiometric TiOj l (c) coherent intergrowth of (a) and (b) along the (120) planes of rocksalt structure. Lines indicate unit cell faces of the superstructures. (After Anderson, 1984.)... 

In ScaTes (214) the occupancy is 1/3 instead of 1/4 and this compound is the only semiconductor of this family of ordered defective phases. 

Superstructures, Ordered Defects Nonstoichiometry in Metal Oxides of Perovskite Related Structuresf... 

Isolated, random point defects and valence defects Defect pair association Rearrangement of coordination environment in isolated defect clusters or microdomains 1- or 2-dimensional assays of ordered defects or reorganized defect complexes Fully defined superstructures or shear structures... 

All the elements of the actinide series from Th to Cm form fluorite-type dioxides, and the series affords an opportunity of studying the nonstoichiometry and ordered defect phases characteristic of the structure. To date, the most complete set of results refers to uranium dioxide, and these are discussed first. 

Lattice dissociation Lattice dissociation with complexing Random substitution at particular sites Different out-of-step distances Ordered defects... 

Short range order (defects) Intermediate range order (band tails) Long range order (crystal)... 

Statistical thermodynamic treatments of defect populations have lead to an explanation of existence of grossly nonstoichio-metric crystals in terms of microdomains of ordered structure. The model considers that the nonstoichiometric matrix is made up of a mosaic of small regions of ordered defect-free structures, the microdomains. To account for stoichiometric variation, one can postulate that at least two microdomains with different compositions occur. However, compositional change might simply arise at the surface of the domain. For example, if there are compositionally identical microdomains, one of which is bounded by an anion surface and one by a cation surface, variation in the two populations can give rise to compositional variation. In a strict sense, as each microdomain is ordered, the concept of a defect is redundant, except for... 

Reeder, R. J., Nakajima, Y. (1982). The nature of ordering and ordering defects in dolomite. Phys. Chem. Minerals, 8, 29-35. 

Tetrahedral Random wurtzite (AI283, (3-Ga283) Ordered defect wurtzite (a-GazSs) Random zinc-blende (7-03283) ... 

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