Characterization of nanorods in BaNb₂O₆-doped Er123 films revealed by cross-sectional transmission electron microscopy

Microstructures of BaNb₂O₆-doped as artificial pinning centers in Er123 films were studied by cross-sectional transmission electron microscopy. BaNb₂O₆-doped Er123 films were grown by a pulsed laser deposition technique. In the cross-sectional transmission electron microscopy observation, the presence of nanorods with 5 nm-25 nm diameter, which contain niobium, was confirmed from bright-field images and energy-dispersive X-ray spectroscopy elemental map images, respectively. The crystal structure of the nanorod was determined to be cubic perovskite from selected area electron diffraction patterns by comparing with that of the SrTiO₃ substrate. The axial length of nanorods in the Er123 film was calculated, using selected area electron diffraction patterns, as 0.841 nm, which is in good agreement with the axial length of Ba(Er_0.5Nb_0.5)O₃, 0.8427 nm, provided by X-ray diffraction data. Furthermore, parallel Moiré fringes were observed in the bright-field images, and the relationships between the lattice planes and Moiré fringes were investigated. The spacings of the Moiré fringes were 3.6 nm, and 2.3 nm, which correspond to the 006 and 200 reflections for Er123 and the 004 and 400 reflections of the nanorods, respectively. It is confirmed for the first time that BaNb₂O₆-doped into the Er123 film transforms to Ba(Er_0.5Nb_0.5)O₃ nanorods with a cubic perovskite structure.