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 Y<sub>2</sub>O<sub>3</sub>, BaCO<sub>3</sub>, 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 YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-</sub><sub>d</sub> compound was reached (up to ~95 %) after sintering at 936 °C. Raman spectra demonstrate vibrational modes characteristic of the YBCO composition: O(4)-A<sub>g </sub>mode in the range from ~479 cm<sup>-1 </sup>to ~496 cm<sup>-1</sup>; O(2, 3)-A<sub>g</sub> mode in the range from ~436 cm<sup>-1 </sup>to ~447 cm<sup>-1</sup>; O(2, 3)-B<sub>lg </sub>mode in the range from ~307.5 cm<sup>-1</sup> to ~334 cm<sup>-1</sup>. 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.