Indexing of the X-Ray Diffraction Pattern |
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Determination of the unit cell metric of the compounds synthesized is performed by the machine method of indexing diffraction patterns of polycrystalline substances. This method is based on algorithms that allow the experimental values of interplanar distances (1/d2 ) of reflections to be matched with the “crystallographic” coordinates of atomic lattices (Miller indices hkl) that cause them. These mathematical algorithms are based on the Ito method and are implemented in the corresponding software packages, in particular in [Serykh V.P. Structural analysis in powders and algorithms// Collection of programs. –Kharkov: Rotaprint HFTI. –1980. –112 p.].
Correct diffraction pattern, which reflections’ coordinates satisfy the inequalities: where Qi , DQi are the array element (1/d2) and its uncertainty, respectively , Qmax is the last array element, a is a value considering the extinction conditions, allows us to determine the translational Bravais parallelepiped of the size limited by the ratio :
where V is the volume of the translational Bravais parallelepiped, nåêñï. is the number of reflections. If the diffraction pattern is recorded from a single-phase substance, a set of indexing programs gives reliable results regarding the metric (refined values of lattice parameters) and symmetry (diffraction class) of the crystal lattice of the phase studied. .
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