HYSTERESIS OF THE CURRENT-VOLTAGE CHARACTERISTICS AND ELECTRIC-FIELD EFFECTS IN BULK YBCO SUPERCONDUCTORS

Some YBCO ceramics have been found to exhibit hysteresis of the curren t/voltage, I/V, characteristics, which reveals at a certain current I- f greater than critical current I-c a transition with switch from one branch of the I/V curve to another. In present work, the influence of an electric field at 77 K on hysteresis of IN curves of ceramic YBCO/A g and YBCO after hydrogen treatment has been studied. It was establish ed that in strong electric field (120 MV/m) the conductivity increases at current I>I-c, the field effect being observed only in the upper b ranch of hysteresis loop. The electric field effect in YBCO after hydr ogen treatment is reversible. The observed effects are assumed to be a ssociated with a change of grain boundary weak links from S/I/S-to S/N /S-type in the course of hydrogen treatment or addition of silver into ceramics.