Microstructure of i n s i t u epitaxially grown superconducting Y-Ba-Cu-O thin films

The microstructure of in situ epitaxially grown Y-Ba-Cu-O thin films on (001) SrTiO3 substrates was studied using cross-sectional transmission electron microscopy. The films, prepared by pulsed laser deposition at substrate holder temperature of 650 °C without post-annealing, exhibit zero resistivity above 90 K and critical currents exceeding 106 A/cm2 at 77 K. The films are of heavily faulted single crystalline structure with the c axis approximately perpendicular to the substrate (001) surface. We suggest that, due to the fast quenching and low substrate temperature, crystalline defects and chemical fluctuations are locked into a faulted structure after each laser pulse. Despite their rather imperfect microstructure, the films are free from macroscopic grain boundaries and secondary phases and possess superb superconducting properties.