REBa2Cu3O7-x (REBCO) compounds have appeared as interesting materials for the manufacture of Coated Conductors (CCs) due to their excellent current carrying capacity. Modifying REBCO films on the nanoscale leads to nanocomposite films which are obtained by the introduction of artificial nanoscaled defects of non-superconducting secondary phases in the REBCO matrix. This improves the in-field performance of the material even further, since magnetic flux lines are effectively immobilized due to the pinning character of the resulting nanodefect landscape. This widens the possibilities for power applications as broader magnetic field and temperature ranges are accessible.
Chemical solution deposition (CSD) is a technique starting from a complex metal-organic precursor solution, which has been demonstrated to be a useful method to prepare REBCO nanocomposite films with spontaneously self-segregating secondary phases (“in-situ particles”). In these films, the nanoparticles tend to orient randomly within the REBCO matrix creating a high density of defects, which generates nanostrain that ultimately leads to a strong enhancement of the isotropic pinning force. Hence, precise control of the particle size and its orientation play a key role. So far, there is still ample room for performance improvement where control of the particle size and its orientation is an important issue, which is a challenge. For this purpose, an approach towards “ex-situ nanocomposites” via CSD is investigated, for which a colloidal solution of preformed nanocrystals is added to a REBCO precursor solution. This has the advantage that the nanocrystals can be tuned separately.
In this work, we compared the superconducting properties and structural features of ~200 nm thick GdBa2Cu3O7-x nanocomposite films containing different concentrations of oxide nanoparticles prepared via the in-situ and ex-situ approaches. For the in-situ approach we used self-assembled BaHfO3 (BHO) nanoparticles while in the case of the ex-situ approach we started from a solution containing colloidal preformed HfO2 nanocrystals. X-ray diffraction measurements were used to evaluate the GdBCO film texture, nanoparticle orientation and to quantify the nanostrain. Advanced scanning transmission electron microscopy was performed to identify nanoparticle size and distribution as well as the GdBCO microstructure. Transport measurements were carried out to examine the vortex pinning characteristics.
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