Quantitative phase analysis by combining the Rietveld and the whole-pattern decomposition methods

The Rietveld quantitative phase analysis of polycrystalline mixtures is a model-dependent method. The absence of any structural information about even one phase in the mixture prevents the application of the method; on the other hand, the availability of a structural model that is not sufficiently representative of real data can actually reduce the accuracy of the weight-fraction estimates. In these cases, when the experimental pattern of one (or more) pure phase(s) with unknown or imperfectly known crystal structure is available, the whole-pattern decomposition techniques can be applied to extract a list of `observed' amplitudes to be used instead of those calculated from the model. Observed and calculated amplitudes can be successfully combined to carry out the Rietveld quantitative phase analysis of even complex structure mixtures, provided that the initial amplitudes are correctly placed on the absolute scale. In the absence of any structural model, the absolute scale supplied by the Wilson plot technique can be applied. A general scheme of the method is proposed here; it has been implemented into the program QUANTO and tested on real zeolites mixtures. The method is basically independent of the program used for the extraction of the integrated intensities.