Effect of Ar heat treatment on oxygenated R1−x Ca x Ba2Cu3O7−δ (R = Y, Sm) superconductors

摘要

The influence of heat treatment, at 450°C in Ar environment, on oxygenated (6.72 < 7 − δ < 6.93) samples of R1−x Ca x Ba2Cu3O7−δ (i.e. R(Ca)-123, with R = Y, Sm) with 0 < x < 0.3 has been investigated. Measurements of oxygen loss, normal state resistivity behaviour ρ(T), superconducting critical temperature T c and transition widths reveal that Ar treatment effects both the series differently. The Sm(Ca)-123 samples, for all values of x, show a considerable loss of oxygen (Δδ(x) = 0.4 to 0.6) and decrease in T c (ΔT c(x) = 35 to 55 K). Whereas, surprisingly, the Y(Ca)-123 samples show a much smaller loss of oxygen (Δδ(x) = 0 to 0.3), along with a decrease in T c for x < 0.2 and an increase in it for x > 0.2. In particular, the x = 0.3 sample shows a negligible change in oxygen content accompanied by an increase of 20 K in T c. These and host of other observations suggest that the presence of Ca may influence the oxygen loss mechanism in these series.