  [100]-tilt grain-boundary YBa2Cu3O7-x (YBCO) junctions are promising for
investigation of macroscopic quantum phenomena in high-Tc Josephson junctions.
However, fabrication of the [100]-tilt grain-boundary YBCO junctions with a
high resistance, which are required to study quantum effects, is difficult
because of a high transparency of a tunnel barrier in this type of junctions.
Here, we demonstrate a modification of grain-boundary barrier properties with a
new approach to an oxygen electromigration in the YBCO grain-boundary junctions
when the oxygen diffuses under an applied electric field from the
grain-boundary to a BaTbO3 layer deposited atop of an YBCO film. Using this
approach, we changed the normal-state resistance of the junctions from tens to
several hundred Ohms without a degradation of their characteristic voltage IcRn
and determined a barrier height and thickness by measuring the quasiparticle
tunnelling current.
