Accuracy in Rietveld quantitative phase analysis with strictly monochromatic Mo and Cu radiations

This chapter is based on an article Accuracy in Rietveld quantitative phase analysis: a comparative study of strictly monochromatic Mo and Cu radiations by Leon-Reina et al. [(2016), J. Appl. Cryst. 49, 722–735]. It reports Rietveld quantitative phase analyses using laboratory-based Mo and Cu radiations where synchrotron powder diffraction [λ = 0.77439 (2) A] has been used to validate the most challenging analyses. From the results for three series with increasing contents of an analyte (inorganic crystalline phases, organic crystalline phases and a glass), it is inferred that Rietveld analyses from high-energy Mo Kα1 patterns have slightly better accuracies than those obtained from Cu Kα1 diffraction data. This behaviour was established from the results of calibration graphs obtained through the spiking method and also from Kullback–Leibler distance-statistic studies. The better accuracies achieved when using Mo Kα radiation can be attributed to the higher penetration of Mo K radiation compared with Cu radiation, and hence the larger number of crystallites that diffract with Mo radiation; the higher energy also allows the recording of patterns with fewer systematic errors, even though the diffraction power for Mo radiation is lower than for Cu radiation. Limits of detection (LoDs) and limits of quantification (LoQs) have also been established for the studied series. For similar recording times, LoDs in Cu patterns (∼0.2 wt%) are slightly lower than those derived from Mo patterns (∼0.3 wt%). The LoQ for a well crystallized inorganic phase using laboratory powder diffraction was established as close to 0.10 wt%, as stable fits were obtained. However, the accuracy of these analyses was very poor, with relative errors close to 100%. Only contents higher than 1.0 wt% yielded analyses with relative errors lower than 20%.