Ca induced line defects and superconductivity in YxSr2Cu2GaO7

The microstructure of Ca doped Y 1− x Ca x Sr 2 Cu 2 GaO 7 and Ca substituted YSr 2− x Ca x Cu 2 GaO 7 have been investigated by electron microscopy. A common feature found in the Y 1− x Ca x Sr 2 Cu 2 GaO 7 superconductors is the existence of line defects, which are not observed in non-superconducting YSr 2− x Ca x Cu 2 GaO 7 . At the higher doping level, x ≈ 0.35, the line defects develop into modulated structures. The transition temperature and Meissner fraction increases with the doping level as does the defect concentration, indicating that the defects and superconductivity in these materials are interrelated. The line defects are associated with an asymmetrical distortion ( a p ≠ b p ) of the gallium-oxygen plane which plays a similar role to the copper-oxygen chains in YBa 2 Cu 3 O 7−° .