| Recap |
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this Lecture you have learnt the following |
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Summary |
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In this lecture we have studied how systematic absences are brought about in the diffraction patterns of different lattices. The emphasis was on cubic lattices. The scattering function is derived from the electron density and the resultant of the scattering functions of all the atoms in the unit cells (weighted by their phases and their effective number in the unit cell) gives the structure factor F h k l whose square is proportional to the diffracted intensity I h k l . |
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Since only the square of Fh k l is measurable, the square root of Ih k l can be determined except for a phase factor e i
 . Methods to circumvent the phase problem were listed. The difference between the diffraction patterns of SC, BCC and FCC lattices was illustrated in Fig (19.2) and rationalized in section 19.3. Diffraction techniques using neutrons and electrons were mentioned in section 19.4 and the special advantages of these methods were indicated. |
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