Effect of Ar heat treatment on oxygenated R_1−xCa_xBa₂Cu₃O_7−δ (R=Y, Sm) superconductors

Abstract

The influence of heat treatment, at 450°C in Ar environment, on oxygenated (6.72<7−δ<6.93) samples of R_1−xCa_xBa₂Cu₃O_7-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.