Defect and dopant properties of the oxyfluoride superconductor Sr2CuO2F2+delta

Computer simulation techniques are used to investigate the defect and dopant properties of the oxyfluoride superconductor, ST2CuO2F2+delta. The observed La2CuO4-type structure is correctly reproduced by our interatomic potential model. Defect calculations find that the most favorable fluorine interstitial position is near the ideal site and is associated with significant local relaxation, in accord with diffraction studies. A variety of redox reactions relevant to high-T-c behavior have been examined. Our results confirm that oxidation, involving fluorine incorporation at interstitial sites, is the most favorable process to introduce the holes necessary for superconductivity. We also consider the energetics of a range of dopant substitutions (alkali and alkaline-earth ions) at the Sr site.