Remarkable influence of heat treatment on the structural and superconducting properties of (Y 1– x Sm x )(SrBa)Cu 3 O 6+ z

We report here on the preparation, effect of heat treatments, X‐ray diffraction and AC magnetic susceptibility measurements in the high T c superconductor (Y 1– x Sm x )(SrBa)Cu 3 O 6+ 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 T c 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 T c from 81.5 K to 85 K. For each x , the [AO] heat treatment increases ε (for 0 ≤ x ≤ 1) and T c (for x ≥ 0.4). We observed a remarkable correlation between δ T c ( x ) = T c [AO] – T c [O] and δ ε ( 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)