Remarkable Influence of Heat Treatment on the Structural and Superconducting Properties of ${\rm LnSrBaCu}_{3}{\rm O}_{6+{\rm z}}$

Abstract

We report here on the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility measurements and effect of heat treatments in LnSrBaCu3O6+z (Ln = rare earth = Eu, Sm, Nd). Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. When the ionic radius r(Ln+3) increase, the orthorhombicity epsiv = (b - a)/(b + a) decrease with Tc[O] and Tc[AO]. For each r(Ln+3), the [A,O] treatment increases epsiv (except for Nd), Tc, the distance d[Cu(2) - Ln] and decrease d[Cu(1) - O(1)]. Tc increases remarkably by 10 K, 6 K and 6 K to Tc[AO] = 78 K, 85 K and 87 K, respectively for Ln = Nd, Sm and Eu. Remarkable correlations were observed. A combination of several factors such as the r(Ln+3), decrease in d[Cu(1) - O(1)]; increase in cationic and chain oxygen ordering; and in-phase purity for the [AO] samples may account for the observed data.