Optimizing Nanocomposites through Nanocrystal Surface Chemistry: Superconducting YBa₂Cu₃O₇ Thin Films via Low-Fluorine Metal Organic Deposition and Preformed Metal Oxide Nanocrystals

Abstract

Achieving low cost, safe, reproducible and high performance superconducting thin films of YBa2Cu3O7-δ is essential to bring this material to the energy market. Here, we report on the chemical solution deposition of YBa2Cu3O7-δ nanocomposites from environmentally benign precursors with a low-fluorine content. Preformed ZrO2 nanocrystals (3.5 nm) were stabilized in a methanolic precursor solution via two strategies: charge stabilization and steric stabilization. Counter-intuitively, charge stabilization did not result in high quality superconducting layers, while the steric stabilization resulted in highly reproducible nanocomposite thin films with a self-field Jc of 4-5 MA cm -² (77 K) and a much smaller decay of Jc with magnetic field compared to YBa2Cu3O7-δ without nanocrystals. In addition, these nanocomposite films show a strong pinning force enhancement and a reduced Jc anisotropy compared to undoped YBa2Cu3O7-δ films. Given the relationship between the nanocrystal surface chemistry and final nanocomposite performance, we expect these results to be also relevant for other nanocomposite research.-2 -

Influence of Ba2+ consumption and intermediate dwelling during processing of YBa2Cu3O7 nanocomposite films

“…The nucleation and growth of TFA‐based or reduced fluorine‐based YBCO systems can be found in literature and is described as the ex situ BaF 2 process . Generally, it is reported that the formation of BaF 2 instead of BaCO 3 occurs when a fluorine content of more than 15.4% is used .…”

“…In this work, a homogeneous distribution of the ZrO 2 nanocrystals throughout the layer is observed, and no accumulation of ZrO 2 nanocrystals on the LaAlO 3 interface can be observed in the pyrolyzed films as confirmed via TOF‐SIMS analysis (Figure A). The use of a copolymer as stabilization ligand leads to a spread‐out of nanocrystals in the pyrolyzed matrix because of good nanocrystal surface chemistry . This spread‐out of nanocrystals is a very important step to avoid the tendency to accumulations of nanocrystals during the growth.…”

“…YBa 2 Cu 3 O 7− δ precursor solutions with a 66% reduction in fluorine content were prepared by dissolving Y‐propionate, Ba‐TFA, and Cu‐propionate in an Y:Ba:Cu ratio of 1:2:3 in methanol. Small 3‐5 nm cubic ZrO 2 nanocrystals (distorted tetragonal crystal structure) in toluene were synthesized and purified according to De Keukeleere et al . To transfer these as‐synthesized nanocrystals to polar solvents (eg, methanol), a ligand exchange with a phosphonate‐containing copolymer was introduced, according to Rijckaert et al .…”

“…Small 3‐5 nm cubic ZrO 2 nanocrystals (distorted tetragonal crystal structure) in toluene were synthesized and purified according to De Keukeleere et al . To transfer these as‐synthesized nanocrystals to polar solvents (eg, methanol), a ligand exchange with a phosphonate‐containing copolymer was introduced, according to Rijckaert et al . These copolymer‐stabilized nanocrystals were finally added to the highly ionic YBCO precursor solution, resulting in ZrO 2 ‐doped YBCO precursors solutions.…”

“…Currently, some research has already investigated on the link between the influence of preformed nanocrystals and its surface chemistry with the final YBCO properties. It has been discovered that preformed nanocrystals can lead to better pinning properties while a choice of ligands is very crucial to obtain good YBCO properties . Nevertheless, understanding of nucleation and growth mechanism of undoped and nanodoped YBCO films during the CSD process of TFA‐MOD methods should be essential to improve the superconducting properties.…”