Effect of Nanodiamond on the Growth of YBa₂Cu₃O_7-δ Film Prepared by Metal Organic Decomposition

The in-field superconducting transport properties of YBa₂Cu₃O_7-<i>δ</i> (YBCO) film can be significantly improved through the introduction of nanosized defects that may have a beneficial effect on film properties in the conditions generally requested for fusion applications, i.e. low temperatures and high magnetic fields. The incorporation of different metal oxides as secondary phases into YBCO has been extensively investigated in the past. On the contrary, Nanodiamond (ND) introduction in YBCO film (YBCO-ND) has never been reported until our preliminary study on chemical solution deposited YBCO-ND film grown by Metal Organic Decomposition approach and the “<i>ex situ</i>” route using ND as preformed nanoparticle. Our first attempts showed ND potential for the improvement of YBCO transport properties [1]. In fact, ND suspension in YBCO compatible solvent, i.e. propionic acid, was prepared and nanoparticles with uniform size below 10 nm were obtained. Despite the uncertainty and the low amount of nanoparticles concentration, ND suspension was used for YBCO precursor solution preparation and epitaxial films were obtained. An improvement of film morphology and superconducting properties was observed. Therefore, further investigations of ND influence on YBCO nucleation and growth appeared to be necessary.<br/>In the present work, the effect of ND on the YBCO nucleation mechanism has been evaluated in order to elucidate the role of ND in promoting film growth. A detailed study on YBCO-ND films quenched at different temperatures of the crystallization process was carried out. Results showed that the reaction responsible for YBCO nucleation appeared effectively affected by ND. Some hypotheses as well as some possible and positive implications of this study will be provided.<br/>Furthermore, ND functionalization has been explored in order to favor the interaction between nanoparticle and solvent and, consequently, to obtain higher and precise ND concentrations, in addition to a more stable precursor solution. Different routes have been attempted. The oxidation through acidic treatment resulted in dramatically decrease nanoparticle stability and dispersibility in YBCO solvent. Therefore, the route of functionalization by radical chemistry was exploited due to its general high efficiency under mild operative conditions. In particular, the work aimed to set up suitable experimental conditions to selectively hydroxylate ND tertiary C-H bonds by means of dioxirane chemistry. It is worth noticing that, so far, such radical route was experimented only on simpler diamondoids system. The results thus obtained will be discussed.<br/>[1] Pinto et al., Thin Solid Films 2020. Doi.org/10.1016/j.tsf.2019.137696<br/><br/>Acknowledgments<br/>This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.