THE EFFECT OF HIGH HYDROSTATIC-PRESSURE ON TC OF YBA2CU3OX AS A FUNCTION OF THE OXYGEN-CONTENT

The AC-susceptibility chi', chi'' of YBa2Cu3Ox 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 YBa2Cu3Ox 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 dT(c)dp shows an increase from almost-equal-to 0.4 K/GPa to almost-equal-to 4 K/GPa for an oxygen content decreasing from x almost-equal-to 6.93 to x almost-equal-to 6.77. If the oxygen content is reduced further, dT(c)/dp is almost constant, except for a narrow maximum of almost-equal-to 7 K/GPa at x almost-equal-to 6.72. This maximum can be related to the oxygen content, where the transition temperature of YBa2Cu3Ox changes from the 90 K to the 60 K plateau.