Constraints on structural models of ferrihydrite as a nanocrystalline material

摘要: Recently, Michel et al. (2007a) have presented a structure for ferrihydrite that we show to be incorrect. We do this by comparing (1) the sample form factor without adjustable parameters from powder X-ray diffraction data using recently developed method with (2) exactly simulated (Debyesum method) theoretical factors proposed (including vacancy, particle size and shape, positional disorder effects). used pair distribution functions (PDFs) extracted synchrotron fitted calculated PDFs scale peak shape parameters. The PDF gives consistent short-range (coordination sphere) correlations but under-emphasizes intermediate-range represent more stringent constraints on structure. Main characteristic peaks of six-line (lines 2, 3, 4) are not reproduced structural model. expect our offer rigorous tests structures any nanocrystalline materials.