A general method for the recovery of pure powder XRD patterns from complex mixtures using no a priori information: Application of band-target entropy minimization (BTEM) to materials characterization of inorganic mixtures

The recovery of pure component spectra from multi-component mixtures is one of the most common analytical problems in the chemical sciences. In cases where separation of the unknown components is not possible, the problem is often intractable. In materials science research, X-ray diffraction (XRD) and particularly X-ray powder diffraction (XRPD) are perhaps the primary characterization tools. Recently, we introduced band-target entropy minimization (BTEM), an essentially model-free deconvolution technique, applicable to sets of unknown mixture samples and initially applied to liquid-phase characterization (Chew et al., Organometallics, 2002, 21, 1982–1990). In the present study, a set of 12 unknown inorganic powder mixtures were prepared and the XRPD patterns measured. BTEM was then applied. The analysis provided the right prediction that five components were present. Outstanding pure component XRD patterns were obtained for all five components (Pb 3(PO 4) 2, Pb 3(PO 4) 3Cl, ZrO 2, Pb(OH) 2, and PbO) present. These results have implications for a large variety of intrinsically inseparable multi-component mixtures encountered in material science research. These include un-reactive as well as reactive systems, and ex situ as well as in situ studies, involving organic, inorganic and even metallic/alloy components. Initial tests suggest that BTEM may be well suited for recovering the trace component diffraction patterns present and hence greatly aiding material characterization.