EFFECT OF FLUORINATION ON THE STRUCTURE AND SUPERCONDUCTING PROPERTIES OF THE HG-1201 PHASE

A fluorination of the reduced HgBa2CuO4+delta (Hg-1201) with T-c = 61 K resulted first in an increase in T-c upto 97 K and then in a decreas e and even a suppression of superconductivity due to overdoping. Neutr on powder refinements performed on fluorinated HgBa2CuO4Fdelta showed twice the amount of extra fluorine in comparison with those for the ox ygenated Hg-1201 phases with close T-c. This supports the ionic model of doping in Hg-1201: two holes per oxygen and one hole per fluorine. The apical distances in Hg-1201 depend on the number of dopant atoms r ather than on their charge. The exchange of extra oxygen for a double amount of fluorine shortens the apical Cu-O distances, while the in-pl ane distances and T-c do not vary.