INSULATOR-SUPERCONDUCTOR TRANSITION IN NDBA2CU3O6.67 CERAMICS UNDER PRESSURE

For the first time the insulator-superconductor transition in tetragon al NdBa2Cu3O6.67 ceramics has been induced by pressure. The supercondu ctivity (with T-c = 12 K) was first observed after 3.6 h exposure of t he sample to a pressure of 1 Cpa at room temperature. The relaxation o f T-c to the equilibrium value of about 30 K under pressure of 1 Cpa w as observed during 5 days. After the pressure was released the superco nductivity disappeared within 1.3 h. The observed effects are interpre ted as being the direct consequence of charge redistribution between C uO2 planes and CuO chains as a result of the oxygen ordering processes under pressure.