Weak Links in YBCO Nanopowder.

We have prepared YBCO nanopowder by the sol-gel route. The original powder contains weak links as observed by magnetization and microwave absorption measurements. Most of the weak links could be reduced by keeping the powder in ethanol for 30 min in an ultrasonic bath. It was also found that the ultrasonic bath does not affect the superconducting properties of the nanoparticles themselves. The modulation field applied in the microwave absorption measurements was found to have a large effect on the temperature dependence of the absorption. This phenomenon was explained with a phase diagram for the weak links. [ABSTRACT FROM AUTHOR]