Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

R. F. Luccas, L. Gallo

Abstract

The oxygenation process at constant temperature of YBa$_2$Cu$_3$O$_{7-δ}$ (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 $δ$ 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 ($δ$ $<$ 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 $δ$ values below 0.1 and in near a 60 \% for reaching $δ$ 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.

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

Abstract

The oxygenation process at constant temperature of YBaCuO (YBCO) was systematically investigated in the temperature range from 300 C to 800 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 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 ( 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 values below 0.1 and in near a 60 \% for reaching 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.

Paper Structure

This paper contains 5 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Results
  3. Discussion
  4. Conclusions
  5. CRediT authorship contribution statement

Figures (4)

  • Figure 1: Typical behavior of mass evolution of YBCO at constant temperature in an oxygen saturated atmosphere when starting from fully deoxygenated material. Data is shown for two selected oxygenation temperatures: 394 $^o$C and 691 $^o$C. Mass data is normalized by mass of same sample at fully deoxygenated condition ($\delta$$=$ 1). As a guide to the eye, horizontal black lines mark mass values for $\delta$$=$ 0, 0.1, 0.2 and 0.3. Inset shows same data with time (x-axis) in a logarithmic scale.
  • Figure 2: Oxygenation of YBCO powder at constant temperature for different temperatures. The figure shows the mass normalized to the fully deoxygenated mass value as a function of time. The curves indicate the time required for the material to reach oxygen saturation value for each of the temperatures under study. Every curve finished at the oxygen saturation value for their own temperature. The intermediate points correspond to times at which the material reaches the oxygen saturation values obtained at the other temperatures under study. The inset shows a detailed view of the region marked by a dotted rectangle in the main figure. In general, it is observed that at higher temperatures the material reaches oxygen saturation faster, but at lower oxygenation levels (higher $\delta$ values).
  • Figure 3: Evolution of the mass of YBCO material as a function of time during the oxygenation process at constant temperature for 394 $^o$C and 691 $^o$C (continuous lines). At higher temperature, a rapid increase in mass is observed, pointing out a fast oxygen absorption for the material. At lower temperature, the process is slower but leads to higher oxygenation levels (lower $\delta$ values). The dashed curve represents the proposed evolution of the material mass in a mixed-temperature oxygenation process, consisting of an initial oxygenation stage at high temperature (691 $^o$C) followed by a further oxygenation stage at lower temperature (394 $^o$C), with a transition between temperatures at the point indicated by a red dashed circle.
  • Figure 4: Evolution of the mass of YBCO material as a function of time during the oxygenation process at constant temperature for 394 $^o$C and 691 $^o$C. The figure presents the same data as in Fig. \ref{['Fig2']} with the time in the x-axis in linear scale. It can be clearly observed that the temperature switch is proposed at the point where the slope of the mass evolution curve (directly associated with $\delta$) at high temperature becomes lower than that at low temperature. In particular, the protocol proposed here allows to reach to a value of $\delta$$\approx$ 0.12 in less than 60 % of the time needed working only at 394 $^o$C. The inset shows full data for both temperatures.