The effect of O doping upon the critical current density, Jc, across [001] tilt grain boundaries in thin films epitaxially grown onto bicrystalline substrates, was investigated. The grain-boundary misorientation was varied between 0° and 24°. It was observed that, for 24° grain boundaries, the critical current enhancement due to O over-doping could be as large as a factor of 10 when compared to the Jc value for optimum doping (where Tc was greatest). This O-induced enhancement of the grain boundary Jc was similar to that observed for optimized Ca doping. For 15° and 10° grain boundaries, the relative enhancement due to O doping was smaller than that for the 24° grain boundary. It was observed that the grain boundaries often degraded after repeated O treatments; probably because of chemical contamination. Much larger enhancements of the grain boundary critical current density might be achieved by heavy O-doping if the competing degradation could be avoided.

Critical Current of Grain Boundaries in YBa2Cu3Ox Bicrystal Films as a Function of Oxygen Concentration. H.Claus, B.Ma, A.P.Paulikas, R.Nikolova, B.W.Veal, Q.X.Jia, U.Welp, K.E.Gray: Physical Review B, 2007, 76[1], 014529 (11pp)