CA DOPING OF YBA2CU3O7-DELTA SINGLE-CRYSTALS - STRUCTURAL ASPECTS

In this work the structural effects of the Ca substitution in YBa2Cu3O 7-delta (Ca-123) have been studied by X-ray single crystal structure a nalysis for the first time. The structure refinements of three single crystals show that at low Ca concentrations (< 11%) Y3+ ions are subst ituted, while at higher concentrations Ca2+ also replaces Ba2+. Remark ably, no difference in the structural changes has been observed that a re due to the apparent substitution for Ba2+ with Ca2+ in the more hea vily doped samples. Changes in atomic parameters and bond lengths are observed upon Ca doping which are similar in Ca-124 and Ca-247 single crystals. In contrast to ceramic samples, our Ca-123 single crystals a re not superconducting probably due to Al doping from the crucible. Ho wever, considering doped superconductors, the discussion of structural changes with doping is quite interesting as this work is the first st ructure refinement of Ca-123 single crystals.