A methodology of general validity to prepare epitaxial nanocomposite films is reported based on the use of colloidal solutions containing different crystalline preformed oxide nanoparticles (ex-situ nanocomposites). The trifluoroacetate (TFA) metal-organic chemical solution deposition route is used with alcoholic solvents to grow epitaxial YBa 2 Cu 3 O 7 (YBCO) films. For that reason stabilizing oxide nanoparticles in polar solvents is a challenging goal. We have used scalable nanoparticle synthetic methodologies such as thermal and microwave-assisted solvothermal techniques to prepare CeO 2 and ZrO 2 nanoparticles. We show that stable and homogeneous colloidal solutions with these nanoparticles can be reached using benzyl alcohol, triethyleneglycol, nonanoic acid, trifluoroacetic acid or decanoic acid as protecting ligands, thereby allowing subsequent mixing with alcoholic TFA solutions. An elaborate YBCO film growth analysis on these nanocomposites allows the identification of the different relevant growth phenomena, e.g. nanoparticle pushing towards the film surface, nanoparticle reactivity, coarsening and nanoparticle accumulation at the substrate interface. Upon mitigation of these effects, YBCO nanocomposite films with high self-field critical currents (J c 3-4 MA/cm 2 at 77 K) were reached, indicating no current limitation effects associated to epitaxy perturbation, while smoothed magnetic field dependences of the critical currents at high magnetic fields and decreased effective anisotropic pinning behavior confirms the effectiveness of the novel developed approach to enhance vortex pinning. In conclusion, a novel low cost solution-derived route to high current nanocomposite superconducting films and coated conductors has been developed with very promising features.

Although high temperature superconductors are promising for power applications, the production of low‐cost coated conductors with high current densities—at high magnetic fields—remains challenging. A superior superconducting YBa2Cu3O7–δ nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO2 NCs are added to the trifluoroacetic acid based precursor solution and the NCs' stability is confirmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa2Cu3O7–δ, unless a thin seed layer is applied. A 10 mol% ZrO2 NC addition proved to be optimal, yielding a critical current density JC of 5 MA cm−2 at 77 K in self‐field. Importantly, this new approach results in a smaller magnetic field decay of JC(H//c) for the nanocomposite compared to a pristine film. Furthermore, microstructural analysis of the YBa2Cu3O7–δ nanocomposite films reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa2Cu3O7–δ nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic field applications.

GdBa 2 Cu 3 O 7 x -BaHfO 3 (GdBCO-BHO) nanocomposite (NC) films containing 12 mol% BHO nanoparticles were prepared by chemical solution deposition (CSD) following the TFA route on SrTiO 3 (STO) single crystals and buffered metallic tapes supplied by two different companies: Deutsche Nanoschicht GmbH and SuperOx. We optimized the preparation of our GdBCO-BHO solutions with acetylacetone making the film synthesis very robust and reproducible, and obtained 220 nm films with excellent superconducting properties. We show the structural, morphological and superconducting properties of the films after a careful optimization of the processing parameters (growth temperature, oxygen partial pressure and heating ramp). The films reach critical temperatures (T c ) of ∼94 K, self-field critical current densities (J c ) of >7 MA cm 2 and maximum pinning force densities (F p ) of ∼16 GN m 3 at 77 K on STO and T c of ∼94.5 K and J c > 1.5 MA cm 2 on buffered metallic tapes. The transport properties under applied magnetic fields are significantly improved with respect to the pristine GdBCO films. The GdBCO-BHO NC films on STO present epitaxial c-axis orientation with excellent out-of-plane and in-plane texture. The films are, in general, very dense with a low amount of pores and only superficial indentations. On the other hand, we present, for the first time, a systematic study of CSD-grown GdBCO-BHO NC films on buffered metallic tapes. We have used the optimized growth conditions for STO as a reference and identified some limitations on the film synthesis that should be overcome for further improvement of the films' superconducting properties.

To reduce the fabrication costs while maximizing the superconducting and pinning properties of YBa2Cu3O7−δ (YBCO) nanocomposite films, the drop-on-demand ink-jet printing technique was used to deposit colloidal YBCO inks onto LaAlO3 substrates. These inks containing preformed HfO2 nanocrystals were carefully adjusted, prior to the jettability, as the droplet formation depends on the rheological properties of the inks themselves. After carefully adjusting printing parameters, 450-nm thick pristine YBCO films with a self-field critical current density (Jc) of 2.7 MA cm−² at 77 K and 500-nm thick HfO2-YBCO nanocomposite films with a self-field Jc of 3.1 MA·cm−² at 77 K were achieved. The final HfO2-YBCO nanocomposite films contained dispersed BaHfO3 particles in a YBCO matrix due to the Ba2+ reactivity with the HfO2 nanocrystals. These nanocomposite films presented a more gradual decrease of Jc with the increased magnetic field. These nanocomposite films also showed higher pinning force densities than the pristine films. This pinning enhancement was related to the favorable size and distribution of the BaHfO3 particles in the YBCO matrix.

REBa 2 Cu 3 O 7−x (REBCO, RE = rare earth) compounds with different single RE elements were grown via TFA-MOD (metal-organic deposition of trifluoroacetates) to clarify their T c values when grown by the same preparation method and their processing windows; here: the crystallisation temperatures at a constant process gas composition (pO 2 , pH 2 O). We focussed on the lanthanides (Ln) Nd, Sm, Gd, Dy, Ho, Er and Yb as substituents for Y in the REBCO phase and investigated their growth behaviour in terms of resulting physical (inductive T c and J c (77 K)) and structural properties (determined by XRD, SEM, TEM). All phases were grown as pristine films on LaAlO 3 and SrTiO 3 and compared to their respective nanocomposites with 12 mol% BaHfO 3 for in-field pinning enhancement.With regard to T c and J c (77 K), the optima of both values shift towards higher growth temperatures for increasing and decreasing RE ion size with respect to yttrium. Highest T c values achieved so far do not show a trend that can solely be related to the RE ionic size. On the contrary, T c,90 values of the LnBCO compounds from Sm to Er range between 94.0 and 95.3 K and are, therefore, significantly larger than the highest values of the average-size non-lanthanide, Y, with T c,90 = 91.5 K. J c,sf values at 77 K seem to plateau between 5 and 6 MA cm −2 from Sm to Er and are again clearly above the maximum values we ever achieved for Y with 4.2 MA cm −2 . REBCO phase formations of the very small Yb and large Nd turned out to be more difficult and require further adjustment of growth parameters. All REBCO phases investigated here show distinct dependences of T c on the lattice parameter c.

The kinetics of oxygen incorporation (in-diffusion process) and excorporation (out-diffusion process), in YBaCuO (YBCO) epitaxial thin films prepared using the chemical solution deposition (CSD) methodology by the trifluoroacetate route, was investigated by electrical conductivity relaxation measurements. We show that the oxygenation kinetics of YBCO films is limited by the surface exchange process of oxygen molecules prior to bulk diffusion into the films. The analysis of the temperature and oxygen partial pressure influence on the oxygenation kinetics has drawn a consistent picture of the oxygen surface exchange process enabling us to define the most likely rate determining step. We have also established a strategy to accelerate the oxygenation kinetics at low temperatures based on the catalytic influence of Ag coatings thus allowing us to decrease the oxygenation temperature in the YBCO thin films.

Superconducting Y1–xGdxBa2Cu3O7–δ–BaHfO3 nanocomposite films were prepared by chemical solution deposition on SrTiO3 substrates in order to study the influence of the rare earth stoichiometry on their structure, morphology and electrical properties.

High quality CoFe2O4 nanoparticles were synthesized using a one-pot, microwave assisted method, that allows forming stable colloidal solutions in alcoholic solvents, as required for the preparation by Chemical Solution Deposition of hybrid nanocomposite ferromagnetic-high Tc YBa2Cu3O7 superconducting films or devices. We have investigated how the thermal process necessary for the preparation of such epitaxial nanocomposites, involving high temperatures (800 °C) and oxygen partial pressures (1 atm), affects the structure and magnetic properties of the isolated nanoparticles. The NPs were fully characterised by XRD, SQUID, STEM-EELS and XMCD at four different stages of the thermal process. Results show that, despite intermediate changes in the cation distribution occur during the process, the final NP magnetization is stable against the thermal treatment.This result opens up perspectives for the preparation of hybrid YBCO films with embedded magnetic NPs using low-cost chemical-solution methods.