Crystal structure and physical properties of R(Ba1−x Sr x )2Cu3O y (R, Pr) prepared under reducing atmosphere

Abstract: The effects of Sr substitution for Ba on the crystal structure, oxygen content and physical properties of polycrystalline samples of R(Ba1−x Sr x )2Cu3O y (R, Pr) have been investigated. The samples were prepared by sintering at a high temperature under reducing atmosphere, followed by annealing under O2 flow. The structure parameters were refined by the Rietveld analysis of X-ray powder diffraction data. The occupation factors of each site were analyzed under the assumption that a part of Sr ions occupies the R site and pushes the same amount of R ions into the Ba site. For the R, the ratio of Sr on the Nd sites increases with x, from 0 for to 0.11 for . The orthorhombicity decreases continuously with x. On the other hand, for R, the site exchange between Sr and Pr does not occur. The orthorhombicity keeps a high value until and drastically becomes zero at . The electrical resistivity and the Néel temperature increases with x until , and then decreases. These results show that the high decrease rate of in Nd(Ba1−x Sr x )2Cu3O y is attributed to the occupation of Ba sites by Nd and the non-superconductivity of PrBa2Cu3O y is not due to the occupation of Ba site by Pr. It is also suggested that the hybridization of Pr 4f and O 2p orbitals which prevents the replacement of Pr by Sr increases with x until and then abruptly turns to decrease. [Copyright &y& Elsevier]