Raman and x-ray absorption spectroscopy characterization of Zr-doped MOCVDYBa2Cu3O6+δ

Abstract

Metal–organic chemical vapor depositedYBa2Cu3O6+δ (YBCO) films(about 0.9 µm thick) containing varying amounts of added zirconium were examined by Ramanmicroscopy and synchrotron x-ray absorption spectroscopy. The self-field and in-field (1 T,) Jc performance of the YBCO films at 77 K (reported by the group at Oak Ridge NationalLaboratory 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 Zrcontent. Raman measurements on these films showed that the added Zr had littleeffect on YBCO cation disorder up to about 7.5 m/o Zr-added. Cation disorderincreased while Ba–Cu–O content remained relatively constant for Zr additions≥7.5 m/o. In the region ofsharpest descent of Jc with increasing Zr content (2.5–7.5 m/o Zr-added) neither the cationdisorder nor the Ba–Cu–O content showed a systematic variation withJc. Zirconium K edge x-ray absorption near-edge spectroscopy revealedthat virtually all of the added Zr in each sample was present as aBaZrO3-like phase(BZO). The Jc performance of the Zr-added films showed a high correlation with the variations in the next-nearest-neighborZr–M (M = Zr, Y) scattering path amplitude from the extended x-ray absorption finestructure (EXAFS) and the critical temperature over the full range ofZr 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 orCuO. Approximate ranges for the BZO particle dimensions estimated from the EXAFSdata indicated that the mean particle size gets larger with increasing Zr addition.