Chromium substitution effects in Y-124 superconductor prepared by aqueous sol-gel method

Superconducting YBa2(Cu1−x Crx)4O8 (x = 0.01; 0.03; 0.05; 0.10; 0.20) oxides have been synthesized by the aqueous sol-gel method. Effects of chromium substitutions on the properties of compounds were studied by resistivity measurements, X-ray powder diffraction, infrared spectroscopy, electron microscopy and elemental analysis. These data indicated that doping with chromium has a strong effect on the superconducting properties of YBa2Cu4O8 (Y-124) phase. It was demonstrated, that the YBa2(Cu1−xCrx)4O8 samples with x = 0.01, 0.03, 0.05 and 0.10 are superconducting, and the sample with x = 0.20 is not superconducting anymore. Elemental analysis data clearly indicated that Cr enters the Cu sites in the both, Cr3+ and Cr6+ oxidation states. The point defect chemistry approach, which explains the changes of TC by substituting chromium for copper in the YBa2Cu4O8 superconductor, is presented.