Significant Improvement in Ba 1-x K x BiO 3 Grain Boundary Junctions on MgO Bicrystal Substrates by Minimal BaBiO 3 Sputtering

High quality Ba 1- x K x BiO 3 (BKBO) artificial grain boundary junctions were fabricated on MgO (100) bicrystal substrates. We found that extremely-short-time sputtering of BaBiO 3 (BBO) onto MgO substrate prior to BKBO deposition results in a marked improvement in the quality of the BKBO film. Utilizing this technique, a junction with J c =6 kA/cm 2 and Δ V g ≈1 mV at 4.2 K was fabricated. In addition, a junction with a high critical current density of J c =78 kA/cm 2 was obtained.