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

Abstract

AbstractWe report here on the preparation, effect of heat treatments, X‐ray diffraction and AC magnetic susceptibility measurements in the high Tc superconductor (Y1–xSmx)(SrBa)Cu3O6+z (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1). Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. When x increases from 0 to 1; in the samples [O] the orthorhombicity ε = b – a/b + a decreases from 9.35 × 10–3 to 0.38 × 10–3 indicating a structural phase transition from orthorhombic to tetragonal; and Tc decreases from 83 K to 79 K. While in the samples [AO], ε decreases by half from 10.14 × 10–3 to 5.72 × 10–3 with an orthorhombic symmetry. This was accompanied by an increase in Tc from 81.5 K to 85 K. For each x, the [AO] heat treatment increases ε(for 0 ≤ x ≤ 1) and Tc (for x ≥ 0.4). We observed a remarkable correlation between δTc(x) = Tc[AO] – Tc[O] and δε(x) = ε[AO] – ε[O]. A combination of several factors such as change in the Cu(1)‐apical oxygen distance, increase in phase purity, in hole density and chain oxygen ordering for the [AO] samples may quali‐ tatively account for the observed data. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)