Pressure dependence of T-c in strongly underdoped YBa2Cu3O6.41 as a function of pressure-temperature history

The dependence of the superconducting transition temperature T-c(P) of stro ngly underdoped YBa2Cu3O6.41 [T-c(1 bar) similar or equal to 14 K] on hydro static pressure is determined to 7 GPa in an ac susceptibility measurement in a diamond-anvil-cell loaded with dense helium as pressure medium. T-c(P) is found to depend markedly on the temperature-pressure history due to the importance of relaxation processes in the oxygen sublattice. The relaxatio n time tau increases exponentially with pressure, corresponding to an activ ation volume of +4.2 cm(3)/mol. The 'intrinsic' T-c(P)-dependence (that dev oid of relaxation effects) is determined whereby T-c initially increases wi th pressure, passes through a maximum near 17 K at 2 GPa, and falls below 1 .6 K above 7 GPa. (C) 1999 Published by Elsevier Science B.V. All rights re served.