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

Abstract     This chapter is mainly based in the article entitled “Accuracy in Rietveld quantitative phase analysis: A comparative study of Mo and Cu strictly monochromatic radiations” by León-Reina et al., Journal of Applied Crystallography (2016). It reports Rietveld quantitative phase analyses using laboratory based Mo and Cu radiations where synchrotron powder diffraction (λ = 0.77439(2) Å) 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 has been established from the results of the calibration graphics obtained through the spiking method and also from Kullback-Leibler distance statistic studies. We explain this outcome, in spite of the lower diffraction power for Mo-radiation when compared to Cu-radiation, due to the larger volume (and hence a larger number of crystallites) tested with Mo and also because higher energy allows the recording of patterns with fewer systematic errors. Limits of detection (LoD) and limits of quantification (LoQ) 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%. LoQ for a well crystallised inorganic phase using laboratory powder diffraction was established 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%.