Remarkable influence of heat treatment on the structural and superconducting properties of (Y1–xPrx)(BaSr)Cu3O6+z

Abstract

AbstractWe report here on the preparation, X‐ray diffraction (XRD), Seebeck effect, AC magnetic susceptibility, resistivity measurements and effect of heat treatments in the high Tc superconductor (Y1–x Prx)(BaSr)Cu3O6+z . Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. When x increase, the oxygen content (6+z) of the samples decrease slightly from 6.9 to 6.8 as determined by our iodometry measurements. The orthorhombicity ϵ = (b ‐a)/(b +a) decreases to zero at xt [O] = 0.6 and xt [AO] = 0.75. These indicate a structural phase transition from orthorhombic to tetragonal at xt. Whereas, Tc decrease to zero at xc [O] = 0.7 and xc [A,O] = 0.75. Therefore the [A,O] heat treatment increase xc. Note that ϵ decrease with Tc as foreseen. However, for a given x the [AO] heat treatment makes increase ϵ (Tc). Independently of heat treatment, a increase with x, whereas b decreased to its minimum at xt. For a given x < xt, the heat treatment [AO] makes decrease a and increase. A remarkable correlations were observed between Tc (x) and ϵ (x); and between the variation δTc (x) = Tc [AO]‐Tc [O] and δϵ (x). A combination of several factors such as decrease in the Cu (1)‐apical oxygen distance; cationic order of Prx on the (Sr,Ba) site along c axis, chain oxygen ordering on (O4,O5) sites; increase in p and in‐phase purity for the [AO] samples may qualitatively account for the observed data. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)