50 K ENHANCEMENT OF T-C BY PRESSURE IN THE HG-2212 SUPERCONDUCTOR

The superconducting properties of mercury cuprates are extremely sensi tive to compression. The highest transition temperatures obtained up t o date have been measured on Hg-1223 at 25-30 Gpa (T-c similar to 164 K at the onset) and imply an increase of about 20 K with respect to th e ambient pressure T-c0. We report here the largest total pressure eff ect (> 50 K over a span of 20 GPa) ever observed for several samples o f bi-mercury layer Hg2Ba2(Y1-xCax)Cu2O8-delta compositions. Different Ca doping levels give different initial T(c)s but retain the same stro ng pressure dependence. The large T-c increase with pressure for all t he Hg-based compounds, independently of their doping level, is reveali ng the existence of a common structural parameter, which identificatio n will be a guide for future synthesis efforts of record-high T-c mate rials. (C) 1997 Elsevier Science Ltd.