Tests on Simulated and Real Data

4 RESULTS AND DISCUSSION 10.4.1 Tests on Simulated and Real Data 

The DDM algorithm can be readily adapted to any full-profile refinement routine. It was included into the computer program DDM, which is based on a modified and corrected code of BDWS-9006PC. A variant of DDM has recently been implemented in the BGMN program. 

Results of DDM refinement for simulated XRD pattern with randomly modulated background and statistical noise added. The simulated (1), calculated (2), difference (3), difference first derivative (4) and difference second derivative (5) profiles are shown at the initial stage (a) and after 15 cycles of DDM (b). The bold dashed line depicts the background curve added. 

Rietveld refinement. Evidently, the reason for the problematic Rietveld refinement of H-atom positions in this example was in the inaccuracy of the background model. 

The successful testing of DDM method for structure refinement purposes allows us to predict its applicability in other fields of powder diffraction, such as the analysis of microstructure and quantitative phase analysis (QPA). Trial runs of DDM for the XRD data supplied by the International Union of Crystallography Commission on Powder Diffraction for the Size-Strain and QPA round-robins gave encouraging results. Respective examples are included in the DDM program package. In particular, the biases in the phase contents determined by DDM refinement for the QPA round-robin samples from the weighted amounts were less than 1 wt.%. 

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