Effect of Heat Treatment on Changes in the Structure of YBCO Superconducting Powders
Powders with a nominal content of the YBCO phase and optimally saturated with oxygen were prepared by solid-phase synthesis using the oxides Y2O3, BaCO3, and CuO. Sintering of the samples was carried out in the temperature and time range from 900 to 936 ºС in 7 stages for ~10-25 hours at each stage. Comprehensive studies of the structure, morphology, and Raman spectra have been carried out. The fabricated samples predominantly have an orthorhombic superconducting phase with a high oxygen content. The maximum content of the YBa2Cu3O7-d compound was reached (up to ~95 %) after sintering at 936 °C. Raman spectra demonstrate vibrational modes characteristic of the YBCO composition: O(4)-Ag mode in the range from ~479 cm-1 to ~496 cm-1; O(2, 3)-Ag mode in the range from ~436 cm-1 to ~447 cm-1; O(2, 3)-Blg mode in the range from ~307.5 cm-1 to ~334 cm-1. The oxygen content in the samples was estimated by various methods. It was found that the concentration of oxygen in intergranular media was lower, on average by ~5 %, than in volume.