Pressure-controlled oxygen order and superconductivity in REBaCuO (RE = Y,Nd) near the metal-insulator transition

Disappearance of superconductivity correlated with an increase of the unit cell volume, V-cell, as a result of the oxygen disordering process caused b y the pressure release was observed for NdBa2Cu3O6.67 in both magnetic and X-ray measurements. Correlation between changes of T-c and V-cell under pre ssure is well described by a simple model based on the O(5) --> O(1) transi tion in the CuOx planes. It was found that due to the oxygen ordering the c ompressibility of NdBa2Cu3O6.67 increases with time by 30%. Superconductivi ty occurs at pressure p(c) = 0.21 GPa. The T-c(p) dependence is a nonlinear function of an applied pressure. The dT(c)/dp reaches value of 80 K/GPa ne ar p(c). Time asymmetry in the processes of oxygen ordering and disordering for both NdBa2Cu3O6.67 and YBa2Cu3O6.38 was found. (C) 1999 Elsevier Scien ce B.V. All rights reserved.