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Next: 5. Accurate Cell Dimensions Up: 4. Interpretation of Powder Photographs Previous: 4.2. Tetragonal and hexagonal structures

4.3 Systems of lower symmetry

Equations for orthorhombic, monoclinic and triclinic systems are more complicated. A general method for dealing with them has been devised by Ito and is amenable to treatment by digital computers; a description of it is given by Lipson and Steeple (1970). But there is no method that can be guaranteed to give an unequivocal answer; some lines may overlap and so cannot be measured accurately, and there will always be odd coincidences which will mislead. The only safe way is to try to obtain a single crystal, deduce the cell dimensions from it and calculate all the possible values of sin2 $\theta$.

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