Increase of YBa2Cu3O7 critical currents by Mo substitution and high pressure oxygen annealing

We have previously shown for powders that Mo substitution into the CuO chains of YBa2Cu3O7 can create effective pinning centres which significantly increase the critical current density (j_c) in 7 T field by a factor of 4 and 10 at 50 and 60 K, respectively. The present work reports on the influence of the Mo substitution and high-pressure oxygen annealing on the pinning properties and critical currents of YBa_2Cu_{3-x}Mo_xO_{7-d} by comparing pure (x = 0, d > 0) and substituted (x = 0.03, d < 0) single crystals. Pinning properties have been investigated by measurements of magnetization loops and calculations of j_c in the ab-plane, in the temperature range from 2 to 90 K and in fields up to 14 T. Depending on the Mo substitution and the oxygen treatment, several types of pinning centres increasing j_c have been revealed and analysed in the frame of Dew-Hughes' and Kramer's models.