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

Abstract
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.