The effect of high hydrostatic pressure on Tc of YBa2Cu3Ox as a function of the oxygen content

Abstract The AC-susceptibility χ′, χ′ of YBa 2 Cu 3 O x polycrystals has been determined under hydrostatic He-pressures up to 0.8 GPa. The experimental data allow a separation to be made of the pressure effect on the superconducting transition temperature T c into two parts, the pressure effect from the weak link structure of the polycrystalline material and the true pressure effect of the bulk material. These investigations have been performed on a series of polycrystalline samples of YBa 2 Cu 3 O x with various oxygen content. Each sample has been cut from the same pellet followed by a careful adjustment of the oxygen content by a heat treatment in air. The true pressure effect of the bulk material d T c /d p shows an increase from ≈ 0.4 K/GPa to ≈ 4 K/GPa for an oxygen content decreasing from x ≈ 6.93 to x ≈ 6.77. If the oxygen content is reduced further, d T c /d p is almost constant, except for a narrow maximum of ≈ 7 K/GPa at x ≈ 6.72. This maximum can be related to the oxygen content, where the transition temperature of YBa 2 Cu 3 O x changes from the 90 K to the 60 K plateau.