Epitaxial Ba1−<i>x</i>K<i>x</i>BiO3 films on MgO: Nucleation, cracking, and critical currents

Abstract

A two-step growth technique is used to obtain (100) oriented Ba1−xKxBiO3 films with good superconducting properties by molecular beam epitaxy. The films are nucleated without potassium at higher temperatures to get the perovskite (100) orientation on (100)MgO. Ba1−xKxBiO3 is then grown at a lower temperature using potassium flux from the decomposition of K2O. The oxygen content of the films is adjusted in a post-growth anneal in oxygen to reduce cracking which can result from oxidation-induced shrinkage. The annealed films have superconducting transitions as narrow as 0.5 K at temperatures between 20 and 25 K. Critical currents in the range of 105 A/cm2 at 4.2 K have been measured by the magnetization hysteresis loop method.