PRESSURE-INDUCED SUPERCONDUCTIVITY IN TETRAGONAL NDBA2CU3O6+X

The appearance of superconductivity and relaxation of the transition t emperature to its equilibrium value T-c approximate to 30 K over the c ourse of five days have been observed in a tetragonal sample of NdBa2C u3O6.67 under 1 GPa pressure. The time dependence T-c(t) correlates wi th a decrease of the room-temperature electrical resistance R(t). The superconducting phase disappears 1.3 h after the pressure is removed. This behavior is explained by a redistribution of charge as a result o f pressure-induced oxygen reordering in the CuOx planes. A large effec t of oxygen ordering on the transition temperature under pressure has been observed near the metal-insulator transition (the largest of all those measured in the 1-2-3 system), along with a nonlinear temperatur e dependence of T-c. (C) 1997 American Institute of Physics.