Crystal Structure - Practical Electron Microscopy and Database - - An Online Book - |
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Microanalysis | EM Book https://www.globalsino.com/EM/ | ||||||||||||||
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A classical definition of a crystal is: A crystal is a substance in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating three-dimensional pattern. [1] Table 3264 summarizes the some basic differences between crystals, glasses, and liquids. Table 3264. Some basic differences between crystals, glasses, and liquids.
A lattice point is known as a motif or basis. We can obtain a crystal structure by combining the lattice with the motif (i.e., crystal structure = lattice + motif). Figure 3264 shows a periodic pattern consisting of a two-dimensional (2-D) net and a motif. The motif is arranged symmetrically and is repeated at each point of the 2-D net to create the periodic pattern, and thus the lattice structure is also symmetric.
Figure 3264. (a) A 2-D net, (b) A motif, and (c) Formed periodic pattern (2-D lattice structure).
Crystalline specimens have to be tilted in a goniometer in TEM in order to: [1] International Union of Crystallography [prior to 1992].
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