Effect of fluorination on the structure and properties of Hg-based superconducting Cu mixed oxides

HgBa2CuO4+delta (Hg-1201) and HgBa2Ca2Cu3O8+delta (Bg-1223) were successful ly fluorinated by XeF2. Fluorination of the reduced Hg-1201 phase causes th e increase of T-c up to 97 K which is close to that for the optimally doped oxygenated sample. Neutron powder refinements performed on HgBa2CuO4Fdelta samples showed that the exchange of extra oxygen for a double amount of fl uorine results in shortening of the apical Cu-O bonds while in-plane ones ( as well as T-c) do not vary. On the contrary fluorination of Hg-1223 result ed in T-c enhancement up to 138 K while oxygenated sample exhibited lower T -c = 134 K. From X-ray and neutron powder diffraction study we suppose that the structural factor responsible for the enhancement of T-c in fluorinate d Hg-1223 is shortening of the in-plane Cu-O distances with (CuO2) layers r emaining practically flat.