Enhancement of the Critical Current Density of YBa2Cu3Ox Superconductors   under Hydrostatic Pressure
  The dependence of the critical current density Jc on hydrostatic pressure to 0.6 GPa is determined for a single 25-degree [001]-tilt grain boundary in a bicrystalline ring of nearly optimally doped melt-textured YBa2Cu3Ox. Jc is found to increase rapidly under pressure at +20 %/GPa. A new diagnostic method is introduced (pressure-induced Jc relaxation) which reveals a sizeable concentration of vacant oxygen sites in the grain boundary region. Completely filling such sites with oxygen anions should lead to significant enhancements in Jc. 
T. Tomita, J.S. Schilling, L. Chen, B.W. Veal, and H. Claus