Effects of Isovalent Substitutions and Heat Treatments on Tc, Orthorhombicity, Resistivity, AC Magnetic Shielding and Irreversibility Line in High-Tc Superconductors

We report here the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility (χac = χ′ + iχ′′), resistivity, iodometric measurements and effect of heat treatments in (Y1−xSmx)SrBaCu3O6+z. Each sample has undergone two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] heat treatment increases the orthorhombicity ε = (b − a)/(b + a) (for 0 ≤ x ≤ 1), Tc (for x ≥ 0.4) and reduced the linear resistivity parameters with a diminution of the interaction of holes with phonons. At all T < Tc and for any applied field Hdc, we observed an enhancement of AC magnetic shielding and the irreversibility line in the samples [AO] for x > 0.5, revealing an improvement in the pinning properties. Remarkable correlations were found. In the [AO] samples, the measured data are explained by the increase in phase purity, in cationic and chain oxygen ordering, psh and the decrease in d[Cu(1)─(Sr/Ba)].