Structure determination of α-CrPO₄ from powder synchrotron X-ray data

Abstract

Knowledge of the ordered atomic structures of crystalline materials is essential in many areas of science. Single-crystal X-ray diffraction is the technique most often used for both solving and refining crystal structures, but recently, powder diffraction methods have become increasingly important. Many structures have been successfully refined with powder data by using the Rietveld profile method¹to overcome the problem of overlapping Bragg peaks, but attempts to solve structures ab initio, which require a set of well-resolved Bragg intensities, have proved unsuccessful (with a few notable exceptions^2,3). However, a new generation of extremely high-resolution powder X-ray⁴and neutron⁵ diffractometers now allows the ab initio determination of crystal structures from powder data (see ref. 6). As part of our study of the structural and magnetic properties of transition-metal phosphates^7,8, we present here the structure of α-CrPO₄, solved from powder X-ray data obtained at the Brookhaven National Synchrotron Light Source, and confirmed by a Rietveld analysis of neutron data collected with the diffractometer Dla at the Institut Laue–Langevin, Grenoble.