High-pressure effects in fluorinated HgBa₂Ca₂Cu₃O_{8 + δ}

We have measured the pressure sensitivity of T-c in fluorinated HgBa2Ca2Cu3O8+delta (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa. We obtained that T-c increases with increasing pressure, reaching different maximum values, depending on the F doping level, and decreases for a further increase of pressure. A new high T-c record (166K +/- 1K) was achieved by applying pressure (23 GPa) in a fluorinated Hg-1223 sample near the optimum doping level. Our results show that all our samples are at the optimal doping, and that fluorine incorporation decreases the crystallographic a-parameter concomitantly increasing the maximum attainable T-c. This effect reveals that the compression of the a-axis is one of the keys that controls the T-c of high-temperature superconductors.