Structural aspects, superconductivity and thermal properties of Pr in the La1-xPrxCaBaCu3O7-δ system with 1.0≥x≥0.0

We report on the structural aspects and superconductivity of the La1-xPrxCaBaCu3O7-delta system (RE: 1113) with x = 0.0, 0.1, 0,2, 0.3, 0.4, 0.5, 0,6, 0.7 and 1.0. X-ray diffraction studies show that Pr substitutes isostructurally in LaBaCaCu3O7-delta (La: 1113) until complete replacement of La. The superconducting transition temperature, T-c, determined from AC susceptibility measurements decreases with x. The relative T-c depression due to Pr in the LaBaCaCu3O7-delta system is less in comparison to that found for La site Pr substituted LaBa2Cu3O7 system. Normal state DC magnetism of the Pr substituted samples show a Curie-Weiss paramagnetic susceptibility with deviations below about 10 K. The non-superconducting compounds (x = 0.7, 1.0) display Schottky-type anomalies which are attributed to crystalline electric field effects (CEF). The related entropy change for x = 1.0 sample amounts to Delta S = 7.75 J/mol K. Rietveld analysis on neutron diffraction pattern of x = 0.0 sample shows that 46 at% of the La is occupying the Pa site, in normal Re: 123 unit cell. A similar situation is suppose to occur in case of PrBaCaCu3O7, for which the refinement of Pa and Pr sites is near impossible due to their similar scattering cross-sections for neutrons. Ba site sitting Pr does not contribute to the Pr-4f hybridization with Cu-O conduction band, giving rise to a lower T-N and less effect of Pr on superconductivity of La: 1113 system than for La: 123. The results strengthen extended Pr-4f hybridisation with Cu-O conduction band. (C) 1998 Elsevier Science B.V. All rights reserved.