Manifestation of oxygen order-disorder effects in EuBa 2 − kSr kCu 3O 6 + z

Abstract

We report here on the structural and AC susceptibility measurements of EuBa 2 − k Sr k Cu 3O 6 + z ( k = 0, 0.4, 0.6, 0, 8 and 1). The samples were subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. Whereas the orthorhombicity decreased as a function of Sr ( k) for the [O] samples, it increased for the [AO] samples for k > 0.4. Further, the slope dT c dk decreased remarkably after the [AO] treatment. This slope was found to be different from that observed in the case of YBa 2 − kSr k Cu 3O 6 + z . A maximum increase in the intergranular coupling was found for k = 0.6 after the [AO] treatment. The result cannot be attributed only to a change in the ionic size of the rare earth as expressed by several authors. We propose that in addition to the cation disorder (Sr/Ba), there may be an oxygen disorder in the basal plane. The results observed are the outcome of an interplay between cationic (Sr/Ba) disorder and oxygen disorder. The [AO] treatment seems to enhance certain properties by reducing this oxygen disorder.