Statistical analysis of electron channelling microanalytical data for the determination of site occupancies of impurities

Abstract

A novel method for determining the concentration and distribution across sites of substitutional impurities in crystals is described, as an alternative to the usual ratio method of atom location by the channelling enhanced microanalysis (ALCHEMI) technique. The integrated X-ray counts for emission from impurity and host atom species under strong zone-axis diffraction conditions are analysed using standard multivariate statistical procedures. This enables both the total concentration and the fractional site occupancy of the impurity species to be determined, together with quantitative estimates of the uncertainties in these quantities. This method of analysis is illustrated through the determination of the site occupancy of Fe in a Cr₂MnO₄ spinel. Advantages of this technique include reduced sensitivity both to the effects of delocalization and to the effects of experimental errors compared with standard ALCHEMI analyses.