Pressure Dependence of Successive Phase Transition in YBCO Superconductive Ceramics

Abstract

The ceramic YBa 2 Cu 3 O 7-δ samples composed of sub-micron size grains are considered as random Josephson-coupled networks of 0 and π junctions and show successive phase transition. With decreasing temperature, a transition occurs at first inside each grain at T c1 (just the same with the bulk superconducting transition temperature T c ) and successively another transition occurs among the grains at T c2 (< T c1 ). The negative divergence of nonlinear susceptibility is observed at T c2 and the divergence of nonlinear resistivity is also observed near (just above) T c2 . We have investigated pressure dependence of the successive phase transition in YBa 2 Cu 3 O 7-δ ceramics both under external uniform pressure for the sintered sample and in the pelleterizing process between calcination and sintering. With increasing pressure in the pelleterizing process, the T c2 increases and both the absolute values of linear resistivity and the divergence of nonlinear resistivity (just above T c2 ) decrease. The nonlin...