Ca doping of YBa2Cu3O7−σ single crystals: structural aspects

Abstract In this work, the structural effects of the Ca substitution in YBa 2 Cu 3 O 7−σ (Ca-123) have been studied by X-ray single crystal structure analysis for the first time. The structure refinements of three single crystals show that at low Ca concentrations ( 3+ ions are substituted, while at higher concentrations Ca 2+ also replaces Ba 2+ . Remarkably, no difference in the structural changes has been observed that are due to the apparent substitution for Ba 2+ with Ca 2+ in the more heavily 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 are not superconducting probably due to Al doping from the crucible. However, considering doped superconductors, the discussion of structural changes with doping is quite interesting as this work is the first structure refinement of Ca-123 single crystals.