Crystals notions about

A structure model must be based on a noncontradictory, closed and complete definition. A definition is closed if it does not contain indefinite elements and notions, and it is complete if it includes the description of all structure elements. Thus, for instance, the model in which the amorphous structure is considered as a dislocationally disordered crystal [6.21, 22] becomes not closed if the dislocation structure (in particular, the one of dislocation core) is not defined. At high density of dislocations when their cores may overlap and their structure becomes very indefinite, the model is not closed. The free-volume model [6.23 25], in which the question about geometry and topology of atomic configurations is put aside, is not complete. 

The theoretical density of a solid with a known crystal structure can be determined by dividing the mass of all the atoms in the unit cell by the unit cell volume, (Chapter 1, Section 1.12). This information, together with the measured density of the sample, can be used to determine the notional species of point defect present in a solid that has a variable composition. However, as both techniques are averaging techniques they say nothing about the real organisation of the point defects. The general procedure is ... 

Once students have learnt about basic particle theory (Chapter 2) and then progressed to learning about how many substances consist of molecriles or ions (Chapter 3), it becomes much easier to communicate the chemical notion of a (pure) substance. Distilled water, but not sea water, consists just of water molecules sodirom chloride consists of the same repeating pattern of sodirom and chloride ions throughout the crystal copper consists of a repeating lattice of copper ions with associated electrons. In contrast, in brass,... 

According to O Keefe, the crystal structures of compounds are formed on the basis of the metal structure in which the non-metal atoms are notionally inserted. This problem has been reviewed comprehensively by Vegas et al. [219,220] who have shown that the structures of about a hundred compounds are related to the structures of their parent metals or alloys, in which non-metal atoms simply occupy the interstitial voids. It is interesting that oxides of metals often reproduce the stmctures of the high-pressure phase of initial alloys, i.e. from the structural point of view an oxidation... 

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