Remarkable influence of heat treatment on the structural and superconducting properties of (Y1-xSmx)(SrBa)Cu3O6+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 (Y1-xSmx)(SrBa)Cu3O6+z (x = 01 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 epsilon = b - a/b + a decreases from 9.35 x 10(-3) to 0.38 x 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], 6 decreases by half from 10.14 x 10(-3) to 5.72 x 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 epsilon (for 0 = 0.4). We observed a remarkable correlation between delta T-c(x) = T-c[AO] - T-c[O] and delta epsilon(x) = epsilon[AO] - epsilon[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 qualitatively account for the observed data.