Structure Determination from X-Ray Powder Data

Crystal structure determination from X-ray powder diagrams generally consists of three steps  

For step (2) (structure solution) all classical approaches require the lattice parameters as input. If step (1) failed, i.e., if the powder diagram cannot be indexed, only two methods remain  

At this step, no fit to the experimental data has been made yet. 

The crystal structure of Pigment Blue 80 (4d) was determined analogously, but since the powder diagram could be indexed, the lattice parameters and the space group could be used as input 

Finally, the crystal structures of P-4b and Pigment Blue 80 were fitted to the experimental powder diagrams by Rietveld refinements. For Pigment Blue 80 high-resolution powder data from synchrotron measurements were used. (For P-4b synchrotron measurements do not make sense, since the low quality of the powder diagram is caused by the low crystallinity of the samples, not by the diffractometer.) Details on the lattice energy minimizations and Rietveld refinement of 4b are given in Ref [20]. 

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