Location of interstitial Cr in mullite by incoherent channeling patterns from characteristic X-ray emission

The use of a direct crystallographic technique is reported for locating Cr atomic sites in a mullite containing 11.5 wt% Cr2O3 by monitoring variation s in characteristic X-ray emission rates as a function of fast electron bea m orientation. Systematic examination of two dimensional incoherent channel ing patterns (ICP), formed from characteristic X-ray emissions from Al, Si, and Cr, and recorded near low index zone axis orientations, has enabled th e preferred lattice position of Cr in mullite to be identified as the inter stitial site 0, 0.25, 0. Although the method of atom location by channeling enhanced microanalysis (or ALCHEMI) generally has been applied in situatio ns where introduced minority atom species are accommodated in substitutiona l atomic positions, this study illustrates the identification of an interst itial site of an introduced dopant species. This result does not coincide w ith that derived from X-ray Rietveld refinement. The ICP method is analytic ally robust and. unlike Rietveld refinement, does not require a highly accu rate model of the host lattice framework and composition. ICP analysis ther efore may be more appropriate for this particular application.