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Learn how to apply the selection rules for X-ray diffraction to different crystal structures and symmetries in this recitation module from Chemistry LibreTexts. This module covers the basics of X-ray diffraction, the Bragg's law, the Laue equation, and some examples of diffraction patterns and intensity calculations.
- 12.1.4: Extinctions - Geosciences LibreTexts
In three dimensions, end-centered, body-centered, and...
- 12.1.4: Extinctions - Geosciences LibreTexts
24 de nov. de 2022 · The 7 Crystal Systems. The Body-Centered Cubic (BCC) unit cell can be imagined as a cube with an atom on each corner, and an atom in the cube’s center. It is one of the most common structures for metals. BCC has 2 atoms per unit cell, lattice constant a = 4R/√3, Coordination number CN = 8, and Atomic Packing Factor APF = 68%.
23 de oct. de 2012 · Electron diffraction pattern of Cu taken at the [001] electron incidence, where Cu takes the face-centered cubic lattice. In the case of the face-centered cubic lattice, for the reflections h, k, l having even- and odd-numbered mixed indices, the crystal structure factor takes zero or F (h k l) = 0. Thus, the diffraction spots vanish.
hkl for Face Centered Cubic • Substitute in a few values of hkl and you will find the following: – When h,k,l are unmixed (i.e. all even or all odd), then F hkl = 4f. [NOTE: zero is considered even] – F hkl = 0 for mixed indices (i.e., a combination of odd and even). Ffe e e 1 ih k ih l ik l() ( ) ( ) hkl Selection rules for hkl reflections
Table 1.1 summarizes the selection rules (or extinction conditions as they are also known) for cubic lattices. According to these selection rules, the h2 + J<2 + [2 values for the different cubic lattices follow the sequence Primitive I, 2, 3,4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 16, ... Body-centered 2,4, 6, 8, 10, 12, 14, 16, ...
Body-Centered Cubic Cells. Some metals crystallize in an arrangement that has a cubic unit cell with atoms at all of the corners and an atom in the center, as shown in Figure 2. This is called a body-centered cubic (BCC) solid. Atoms in the corners of a BCC unit cell do not contact each other but contact the atom in the center.
