Nanocrystals: breaking limitations of data analysis

A series of "virtual powder diffraction experiments" was made on models of small single crystals and nanocrystals with the core-shell structure. The results of those experiments were elaborated with application of standard methods of data analysis routinely used for reciprocal and real space analyses of polycrystalline materials. It is shown that the assumption of a uniform crystal structure of nano-materials is not justified and, therefore, application of routine procedures of collection and elaboration of diffraction data may lead to misinterpretation of the experiments and to incorrect conclusions about their structure. Tentative ways of using powder diffraction data to learn about the structure of nanocrystals with different atomic architecture of the core and of the surface of the grains are discussed. A need for elaboration of a model of the atomic structure of an individual nanograin with a non-uniform structure is discussed. An alternative approach to diffraction studies of nanocrystals by presenting the "footprints" of materials under study in the form of plots showing distribution of the experimental apparent lattice parameters as a function of diffraction vector Q, or bond length distribution as a function of r-distances derived from PDF function is suggested.