Improved microstructure and enhanced low-field J_c in (Y _0.67Eu_0.33)Ba₂Cu₃O _7-δ films

This paper reports a study on mixed rare-earth barium-copper oxide superconducting films (Y_0.67Eu_0.33)Ba₂Cu ₃O_7-δ of different thicknesses grown on single-crystal SrTiO₃ substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) were employed to investigate film crystallinity, surface morphology and microstructure. Critical current density in self-field as a function of film thickness and in an applied magnetic field as a function of field strength and direction were also measured. The results show high quality (Y_0.67Eu_0.33)Ba₂Cu ₃O_7-δ films with a smoother and denser surface morphology compared to that of pure YBa₂Cu₃O _7-δ. Athickness-dependent self-field critical current density quantitatively similar to that of pure YBa₂Cu₃O _7-δ was observed, which suggests that the microstructural evolution in terms of increasing surface roughness and microporosity as well as crystallinity degradation is not likely to be playing a critical role in the form of the dependence. (Y_0.67Eu_0.33)Ba₂Cu ₃O_7-δ films also exhibit improved magnetic field performance at low fields over a wide range of orientations in the intermediate angle region, indicating that probable additional random pinning sites were introduced by the substitution of europium in one-third of yttrium sites.