Study on advanced Ce_0.9La_0.1O₂/Gd₂Zr₂O₇ buffer layers architecture towards all chemical solution processed coated conductors

Chemical solution deposition is a versatile technique to deposit functional oxide films with low cost. In this study, this approach was employed to grow multi-layered, second-generation, high-temperature superconductors ("coated conductors") with high superconducting properties. The Ce0.9La0.1O2/Gd2Zr2O7 buffer layer stack and the 200 nm thick YBa2Cu3O7 (YBCO) superconducting layer were sequentially deposited on textured NiW substrates using metal-organic deposition routes.

The surface texture of the Gd2Zr2O7 barrier layer deteriorates when the film thickness increases to 80 nm, although the global texture retains a sharp biaxial orientation, as determined by conventional X-ray diffraction. We paid particular attention to improving the surface quality in terms of crystallographic orientation and local flatness after depositing a Ce0.9La0.1O2 thin film as a cap layer.

From a comprehensive analysis of the surface morphology and misorientation maps constructed by electron backscattering diffraction, it is found that these improvements are mainly attributed to: (i) the preferential nucleation of Ce0.9La0.1O2 crystals on the Gd2Zr2O7 grains with desirable orientations; and (ii) the predominant two-dimensional growth of the Ce0.9La0.1O2 crystals in the layer.

Moreover, the microstructure and superconducting performance of the YBCO superconducting layer were thoroughly characterized and compared with those of films deposited on single-crystal substrates using the same technique. A promising critical current density of 2.2 MA cm-2 (77 K, self-field) was achieved on such an all chemical derived configuration, demonstrating the high quality of the buffer layer stack and the feasibility of using all chemical solution routes for the fabrication of low-cost coated conductors.