119th General Meeting of the KCS

Type Symposium
Area Nanoscale Structural Analysis of Energy Materials
Room No. 402호
Time FRI 09:20-:
Code MAT1-2
Subject Structure determination from powder X-ray diffraction data and its application to characterization of rechargeable battery electrode materials
Authors 홍승태
DGIST 에너지시스템공학, Korea
Abstract Single crystals are the best forms to analyze their crystal structures in most of cases. However, many of new application materials are available only as powder forms. Electrode materials in battery applications are typical examples, and so are the resultant materials after the electrochemical reactions. If a material adopts an unknown and new structure type and only powder form is available, it would be a great challenge to determine the structure. A method has been developed that is a combination and iteration of the powder and the single crystal refinement techniques. Crystal system and unit cell parameters of a totally unknown structure should be determined first, followed by the space group determination. Structure factors are extracted from the powder data by LeBail fit, that are strongly dependent on the structural model. Because the structure is unknown, the initial model is just a trial one, and thus the extracted structure factors usually include serious errors. However, these are treated as single crystal data, and yet quite useful to get a starting model with a routine single crystal technique. The improved model goes back to be used for LeBail fit, and improved structure factors are extracted. The process is iterated until a complete and satisfactory structure is obtained. Rietveld refinement may be employed in the final step. It should be emphasized that the procedure is not always straightforward, especially for materials with unidentified impurities, high symmetry and/or preferred orientations. In this talk, a recent progress in our exploration for new intercalation chemistry of monovalent and divalent ions into various host materials will be presented, focused on structural determination of new phases during the electrochemical reaction.
E-mail st.hong@dgist.ac.kr