Structural and superconducting properties of LaBaCaCu3O7+delta system: a neutron diffraction study

The results on structural aspects and superconductivity of LaBaCaCu3O7+delt a (La:1113) are reported. Both X-ray and neutron diffraction studies have b een carried out on this compound which reveal that this compound crystalliz es in the tetragonal structure (space group P4/mmm). Detailed analysis of t he neutron diffraction data reveals that the Ca, Ba and La atoms in this co mpound are intermixed at the nominal La and Ba sites. Nearly 46% of Ca occu py the usual La-site, while the remaining 54% occupies the Ba-site. Consequ ently, a corresponding amount of La substitutes at the Ba-site. The intermi xing of Ca, Ba and La sites randomizes the chain site oxygens leading to a tetragonal structure for this compound despite an oxygen content close to 7 . These occupancy refinements explain the tetragonal structure of the compo und, despite having an oxygen content close to 7.04, The compound studied p resently shows a sharp superconducting transition at about 68 K. (C) 1999 P ublished by Elsevier Science B.V. All rights reserved.