FUNCTIONAL-PROPERTIES OF SINGLE-CRYSTALS AND LASER-DEPOSITED THIN-FILMS OF CUBIC BKBO SUPERCONDUCTORS

Magnetic properties of a BKBO single crystal and highly oriented in-si tu Pulsed Laser Deposited, PLD, thin film has been investigated. From the hysteretic loops at 5K along three equivalent crystallographic dir ections we find, that along the growth direction of the crystal the cr itical current tends to decrease, which is probably due to the nature of defects introduced during the growth. In the PLD films, we find tha t the rate of cooling to the oxygenation temperature is the important parameter which can be controlled to eliminate micro-cracks and conseq uently enhance the critical current. From SQUID-data on the single cry stal the temperature dependence of the critical current, is found to b e J(c)(T) = J(co)(1 - T/T(c))2 with J(co) = 2.8 10(4) A/cm2 -a value s imilar to that obtained for the PLD films as well. The field dependenc e of the critical current at various temperatures for the single cryst al is well described by an exponential behaviour which may be consider ed to be a consequence of the pair breaking perturbation effect.