The EISI Index: A Search/ Match Tool for Electron Diffraction Phase Analysis

Abstract

The identification of unknown phases using diffraction data and the JCPDS-ICDD Powder Diffraction File (PDF)[1] is a three-step process. First, the Search step rapidly screens the entire PDF to produce a list of candidate solutions that correspond to the unknown phase’s d-spacings and chemistry. Second, the Match step examines closely every aspect of each phase in the candidate list, vs. the unknown, to make the identification. Third, the Decision step: does the solution found make crystal-chemical-thermodynamic sense? A hindrance to the identification process for electron diffraction applications is that the PDF consists of X-ray powder diffraction data. There are two problems: First, while X-ray diffraction intensity data compares well to electron diffraction intensities for randomly-oriented, small-grained specimens, in the main, intensities from the two methods are not the same. The differing intensities exacerbate the problem of unknown phase searching for electron diffraction because X-ray derived Search/Matching methods rely heavily on intensity information.