Chemical solution deposition (CSD) of YBa2Cu3O7−δ (YBCO) nanocomposites from colloidal precursor solutions containing double metal oxide preformed nanocrystals is a promising, costeffective and reproducible approach to produce superconducting films with high critical current density (Jc) and enhanced pinning. Here, the influence of the preformed nanocrystal composition on the microstructure and superconducting properties of the YBCO nanocomposite films is studied, with a focus on establishing a simple and scalable process to grow nanocomposites that can be transferred to grow nano-added coated conductors. Colloidal stable BaZrO3, BaHfO3, BaTiO3 and SrZrO3 nanocrystals (3-6 nm in diameter) were synthesized and added to an environment-friendly low-fluorine YBCO precursor solution. High-quality superconducting layers were grown on LaAlO3 single-crystal substrates from these four nanocomposite precursor solutions in a single deposition process, without the need of a seed layer, yielding Jc of 4-5 MA/cm² at 77 K in self-field. The different YBCO microstructures produced by the four types of nanocrystals and the resulting microstrain of the films are compared and related with the magnetic-field and angular dependence of Jc. We demonstrate the BaHfO3-containing nanocomposite as the best-performing with a homogeneous distribution of nanoparticles with 7 nm in average diameter and a high density of stacking faults, which leads to some of the best superconducting properties ever achieved via low-fluorine CSD. The Jc exhibits a much smoother decay in applied magnetic fields and a much more isotropic behaviour for non-parallel magnetic fields, and the pinning force is increased by a factor of 3.5 at 77 K and 1 T with respect to the pristine film.
Fine
chemical and pharmaceutical companies often employ reactive
crystallization or precipitation to make crystalline intermediates
and finished products. In this work, the supercritical reactive crystallization
route is used for the precipitation of diverse metal–organic
frameworks (MOFs). 1D and 2D MOFs were obtained by reacting either
bypyridil (two linking positions) or triazine (three linking positions)-based
bridging molecules, respectively, with supercritical CO2 soluble M(hfacac)2 (where M = Zn2+ or Cu2+ and hfacac– stands for hexafluoroacetylacetonate).
Additionally, miscellaneous reactions were designed for the crystallization
of 3D MOFs in scCO2, embracing the precipitation of MIL-88B(Fe),
ZIF-8, and a new Zn2+–curcumin coordination polymer.
Obtained crystals in each case were analyzed from a morphological
point of view by scanning electron microscopy analysis to elucidate
potential formation mechanisms. The focus was on the obtained crystal
habits at different reaction points, linked to the precipitation mode
and the role of kinetic and thermodynamic crystal growth control.
The supercritical procedure led to the crystallization of stable hierarchical
nanostructures with micro- and mesoporosity and the precipitation
of nanocrystals.
Efficient and sustainable synthesis of MOFs, as nano or microcrystalline powder, is crucial for the development of new applications for these compounds. For this purpose, the synthesis of Zn 2+ , Cu 2+ and Fe 3+-based MOFs was attempted in this study by using a binary medium consisting of supercritical CO2 mixed with an ionic liquid (emimBF4 or emimBr). In comparison with conventional solvothermal and ionothermal synthesis, MOFs were herein obtained under mild reaction conditions, i.e. 200 bar and 65 ºC, after relatively short reaction periods (< 10 h). To explore the described synthesis method as a generic procedure for the preparation of three-dimensional MOFs, different linkers of the imidazole and carboxylic acid families were tested. Widely investigated MOFs, such as ZIF-8 and HKUST-1, were prepared along with the complex mesoporous MIL-100(Fe). The structure and composition of the synthesized materials were determined by X-ray powder diffraction and elemental analysis. N2 adsorption at low temperature was used to assess the textural properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.