Raman and x-ray absorption spectroscopy characterization of Zr-doped MOCVD YBa₂Cu₃O_6+δ

Metal-organic chemical vapor deposited YBa2Cu3O6+delta (YBCO) films (about 0.9 mu m thick) containing varying amounts of added zirconium were examined by Raman microscopy and synchrotron x-ray absorption spectroscopy. The self-field and in-field (1 T, B parallel to c) J(c) performance of the YBCO films at 77 K (reported by the group at Oak Ridge National Laboratory that fabricated the samples) exhibited an increase on going from 0 mol% (m/o) Zr-added to 2.5 m/o Zr-added but then decreased sharply with increasing Zr content. Raman measurements on these films showed that the added Zr had little effect on YBCO cation disorder up to about 7.5 m/o Zr-added. Cation disorder increased while Ba-Cu-O content remained relatively constant for Zr additions >= 7.5 m/o. In the region of sharpest descent of J(c) with increasing Zr content (2.5-7.5 m/o Zr-added) neither the cation disorder nor the Ba-Cu-O content showed a systematic variation with J(c). Zirconium K edge x-ray absorption near-edge spectroscopy revealed that virtually all of the added Zr in each sample was present as a BaZrO3-like phase (BZO). The J(c) performance of the Zr-added films showed a high correlation with the variations in the next-nearest-neighbor Zr-M (M = Zr, Y) scattering path amplitude from the extended x-ray absorption fine structure (EXAFS) and the critical temperature over the full range of Zr additions and with cation disorder at the higher Zr- added levels (>7.5 m/o). There was no obvious correlation with the amount of residual barium cuprate or CuO. Approximate ranges for the BZO particle dimensions estimated from the EXAFS data indicated that the mean particle size gets larger with increasing Zr addition.