Isovalent Substitution and Heat Treatments Control of Tc, Chain Oxygen Disorder and Structural Phase Transition in High Tc Superconductors (Y1-xNdx)SrBaCu3O6+z

Abstract

We report here on the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility measurements and effect of heat treatments in (Y1&#8722;xNdx )SrBaCu3O6+z. Each sample was subject to 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 ! = (b &#8722; a)/(b + a) (for 0 "x <1), Tc (for x >0.2) and the distance d[Cu(1) (Sr/Ba)] (decrease Tc) for x < 0.25 and decrease it (increase Tc) for x > 0.25. When x increase from 0 to 1, ! decreases to 0 with transition from orthorhombic to tetragonal structure. ![O] decreases with Tc[O]. However, Tc[AO] decreases with ![AO] until x = 0.2, increases for x = 0.4 and after it decreases by 9.8 K to 77.2 K for x = 1 [AO]. Remarkable correlations were observed between Tc(x) and the volume of the unit cell V (x); and between "Tc(x) = Tc[AO]&#8722;Tc[O] and "!(x). A combination of several factors such as decrease in d[Cu(1) (Sr/Ba)]; increase in cationic and chain oxygen ordering; the number psh(x) of holes by Cu(2) O2 superconducting plans and in-phase purity for the [AO] samples may account for the observed data.