Quantitative phase analysis using observed integrated intensities and chemical composition data of individual crystalline phases: quantification of materials with indefinite chemical compositions

Abstract

In a previous report, a new method for quantitative phase analysis (QPA) of multi-component mixtures using a conventional X-ray powder diffractometer was proposed. The formula for deriving weight fractions of individual crystalline phases presented therein includes sets of observed integrated intensities measured in a wide 2\theta range, chemical formula weights and sums of squared numbers of electrons belonging to atoms in respective chemical formula units [Toraya (2016).J. Appl. Cryst.49, 1508–1516]. The latter two parameters required to perform QPA could be calculated from only the information of chemical formulae of individual phases. In the present study, these two parameters are replaced with a single parameter in the form new parameter = (chemical formula weight)/(sum of squared numbers of electrons). As will be expected from this definition, the parameter has nearly equal values for groups of materials consisting of similar kinds of atoms, and its value becomes identical for polytypes or polymorphs having the same chemical composition. That characteristic of this parameter makes it possible to estimate the parameter value not only directly from the chemical composition of the target material itself but also from database-stored chemical analysis data sorted on the basis of mineral or chemical composition. The parameter value is also hardly changed as a result of small compositional variations of the target component material. Therefore, the present method can be applied to QPA of materials not only of definite chemical compositions but also of indefinite chemical compositions without degrading the accuracy of the analysis. This is expected to widen the application to QPA of, for example, natural products containing many kinds of trace elements, industrial materials with complex substitutional replacement of atoms, nonstoichiometric compoundsetc. The theory and some examples of applications are presented. A procedure for quantifying unknown material is also proposed.