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

Abstract

We report here the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility (χ ac = χ′ + iχ″), resistivity, iodometric measurements and effect of heat treatments in (Y 1−x Sm x)SrBaCu 3 O 6+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), T c (for x ≥ 0.4) and reduced the linear resistivity parameters with a diminution of the interaction of holes with phonons. At all T < T c and for any applied field H dc , 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, p sh and the decrease in d[Cu(1)─(Sr/Ba)]. Keywords: chain oxygen order-disorder, heat treatments control of T c , Rietveld refinement structure, phase transition, irreversibility line, AC magnetic shielding, resistivity, (Y 1−x Sm x)(SrBa)Cu 3 O 6+z type-II superconductors