X-ray diffraction studies of the structure of nanometer-sized crystalline materials

Recently, nanometer-sized crystalline materials have been proposed to represent a new solid-state structure which exhibits neither long-range order (like crystals) nor short-range order (like glasses). It was the purpose of this study to test this idea by x-ray diffraction experiments. Nanometer-sized crystalline materials are polycrystals in which the size of the crystallites is a few (1--10) nanometers. Structurally, these materials consist of the following two components, the volume fraction of which is about 50% each: a crystalline component, formed by all atoms located in the lattice of the crystallites, and an interfacial component comprising the atoms situated in the interfaces. It is this interfacial component which was proposed to exhibit an atomic arrangement without short- or long-range order. In order to test this idea, the interference function of nanometer-sized crystalline iron (6-nm crystal size) was measured by x-ray diffraction. The measured interference function was compared with the interference function computed by assuming the interfacial component to be short-range ordered or to consist of randomly displaced atoms (no short- or long-range order). It was found that the experimental interference function can only be matched by the computed one if the interfacial component is assumed to have no short- or long-range order.