Improving YBa$_2$Cu$_3$O$_{7-\delta}$ annealing times through a combining-temperatures route

Abstract

The oxygenation process at constant temperature of YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) was systematically investigated in the temperature range from 300 $^o$C to 800 $^o$C. With this purpose, fully deoxygenated powder samples was exposed to an oxygen saturated atmosphere, and the evolution of their mass was recorded as a function of time using a thermogravimetric balance. Results reveal a strong dependence of both: the oxygenation kinetics and the final oxygen saturation level, on the temperature used for oxygenation. Moreover, results show that higher oxygen temperatures promote faster oxygen absorption but lead to lower saturation levels (higher final $\delta$ values), whereas lower oxygen temperatures result in slower kinetics but enable the system to approach better oxygenation conditions in order to improve the final superconducting properties of the material. In addition to our measurements, a comparative analysis between oxygenation levels at the oxygen temperatures under study was performed in the range around oxygen saturation ($\delta$ $<$ 0.3). Consequently, an oxygenation protocol based on a combination of several oxygenation temperatures is proposed. As a first approach, results from a protocol with just two different oxygenation temperatures is compared with results coming from using just one oxygenation temperature. Outstandingly, a protocol with a first oxygenation step at high temperatures and a second one at low temperatures demonstrates to improve oxygenation times in near a 30 \% for reaching $\delta$ values below 0.1 and in near a 60 \% for reaching $\delta$ values around 0.12. Finally, we trust that our results are of direct application on industry since size of grain used herein are in scales of typical thickness of superconductor tapes.