High-pressure effects in fluorinated HgBa ₂ Ca ₂ Cu ₃ O _{8 + δ}

We have measured the pressure sensitivity of Tc in fluorinated HgBa2Ca2Cu3O 8+ (Hg-1223) ceramic samples with different F contents, applying pressures up to 30 GPa.We obtained that Tc 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 Tc record (166 K 1 K) 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 Tc.This effect reveals that the compression of the a-axis is one of the keys that controls the Tc of high-temperature superconductors.