A Powder Diffraction Database for All Radiations

The Powder Diffraction File (PDF) has it origins over 70 years ago in the compilation of X-ray powder diffraction (XRPD) patterns for chemical phases 1 . The entries over the next 55 years were typically derived from experimental XRPD data, most collected using Cu Kα characteristic X-radiation. For the past 15 years, through collaborations with FIZ, CCDC, and MPDS, an explosion of entries have been added to the PDF via computed XRPD pattern simulations from known single crystal structures. In order to make these patterns suitable for phase identification, many computational and editorial issues were addressed to provide d-spacing and Intensity values as they would be resolved using a typical X-ray powder diffraction instrument. But the inclusion of crystal structures into the PDF database has other far-reaching advantages. The simulation of diffraction patterns is no longer tied to a few characteristic X-ray wavelengths. Addition of continuous anomalous dispersion corrections allows XRPD patterns for any wavelength to be simulated, whether they be lab-based or synchrotron-based. Also, diffraction patterns using particle radiations, namely electrons and neutrons, can also be simulated. The calculation and tabulation of neutron powder diffraction patterns for the crystal structures in the PDF database, using a typical thermal neutron wavelength, has been accomplished 2 and will be made available for phase identification routines with the 2014 release. The kinematical component of SAED and EBSD electron diffraction patterns can be simulated for electron energies typically found in electron microscopes. Twodimensional electron “powder” patterns can be simulated as well, with the capability of overlaying any of these simulated electron diffraction patterns on 2D patterns collected in the microscope. Additionally, a phase identification algorithm for electron diffraction patterns that considers the possibility of having incomplete d-space listings from a limited number of zones has been designed and implemented. A description of the scientific principles behind this expansion of applicability of the PDF will be presented.