This study reports atomic-scale characterization of structural defects in Yb2Ti2O7, a pyrochlore oxide whose subtle magnetic interactions is prone to small perturbations. Due to discrepancies in the reported magnetic ground states, it has become a pressing issue to determine the nature of defects in this system. In the present study, we use atomic resolution scanning transmission electron microscopy techniques to identify the type of defects in the ytterbium titanate single crystals grown by the conventional optical floating zone (FZ) method. In addition to the known point defects of substitution Yb on Ti B-sites, extended defects such as dissociated superdislocations and anti-phase boundaries were discovered for the first time in this material. Such defects were prevalently observed in the FZ grown single crystals (of a darker color), in contrast to the stoichiometric white polycrystalline powders or high quality colorless single crystals grown by the traveling solvent floating zone technique. The lattice strains from these extended defects result in distortions of Yb-tetrahedron. A change of Ti valance was not detected at the defects. Our findings provide new insights into understanding the nature of defects that are of great importance for the physical property studies of geometrically frustrated compounds. Furthermore, this work sheds light on the complicated core structure of superdislocations that have large Burgers vectors in oxides with complex unit cells.

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In this study, it has been shown that the dependence of interdiffusion phenomena in metallic thin films is largely related to the deposition method. Films were prepared by evaporation and unbalanced magnetron sputtering onto glass substrates. Rutherford backscattering spectrometry was used for quantitative compositional analysis of thin films, determination of structures and observation of interdiffusion in bilayer Ni/Ag films. The structures of the films were monitored by x-ray diffraction. The experimental results confirm that evaporated films are in a state of tensile stress, which increases the vacancy concentration and diffusion, whereas sputtered films are under compressive stress, which decreases the vacancy concentration, thus preventing diffusion.