Commensurate structures structural aspects

A discussion of types of inter-layer bonding, layer types and layer matching is followed by a consideration of disorder in such structures, as well as symmetry aspects and some growth mechanisms. Structures transitional between this type of structure and commensurate structures, i.e. structures which are really non-commensurate layers joined at anti-phase boundaries which restore commensurability, are then considered and classified with a detailed consideration of known examples from inorganic chemistry and mineralogy. Finally, some broad, general conclusions are enumerated. 

More abstractly, then, there arc many different dimensions to, and expressions of, the possibility of seeing each individual as a multifaceted unity, having different aspects and being alive to different types of consideration which may be difficult, or even impossible, to render readily commensurable. There are many reasons for and ways of seeing the individual as multi-faceted, as a structure, as subject to inner conflict. 

Classification of composites by the phase inclusion size bears a philosophical aspect how small should a component in the matrix be not to make the term composite material so universal as to include in fact all materials Interatomic distances in molecules and crystals are of 1.5 10 m dimensionality, distances between iterative elements of the crystalline structure are 10 —10 m, while the size of the smallest intermolecular voids in polymers is 10 m. Note that mean nanoparticle size (plastic pigments are 10-8-10 m in size, the diameter of monocrystalline fibers or whiskers is 10 —10 m, glass microspheres are 10 —10 m) is commensurate with parameters of monolithic simple materials. This means that in the totality of engineering materials, nanocomposites occupy a place at the boundary between composite and simple materials. 

We now consider in more detail the consequences of the incommensurate/commensurate nature of a tunnel inclusion compound in terms of diffractionand structural properties, and then energetic aspects end vibrational properties are discussed. 

The opportunity for certain classes of solid inclusion compounds, such as the ID tunnel structures discussed in this article, to form structures that may be commensurate or incommensurate represents an intriguing aspect of these materials, both with regard to understanding the fundamental energetic reasons underlying commensurate... 

Another aspect relating to the structural studies of these phases is the close relationship between the polysulfide structures composed of the three mutually stacked R +, 8 - and (82) - layers. When the imit cell parameters of the phases of one or several related compositions are commensurate, block structures or microtwins are formed, as pointed out by all authors who studied these compounds (Tamazyan et al. 1994, 2000a,b, Podberezskaya et al. 1996, 1998). Twinning, in turn, may lead to incorrect determination of the crystal symmetry, especially if the photo method was used in the study. 8ince the majority of structural studies for the reduced polysulfides utilized this method, only investigations where the composition was refined on the basis of more exact recordings of the intensities and adequate corrections for absorption may be taken into account. 

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