Size, shape, and internal atomic ordering of nanocrystals by atomic pair distribution functions: a comparative study of gamma-Fe2O3 nanosized spheres and tetrapods.

Due to their limited length of structural coherence nanocrystalline materials show very diffuse powder X-ray diffraction patterns that are difficult to interpret unambiguously. We demonstrate that a combination of high-energy X-ray powder diffraction and atomic pair distribution function analysis can be used to both assess the geometry (i.e., size and shape) and determine the internal atomic ordering of nanocrystalline materials in a straightforward way. As an example we consider cubic gamma-Fe(2)O(3) nanosized crystals shaped as spheres and tetrapods.