The fluorine-free metal−organic decomposition (FF-MOD) route is one of the table-top methods for the growth of high-quality superconducting YBa 2 Cu 3 O 7−δ (YBCO) films due to its advantages of being environmentally friendly and having a faster film deposition rate. However, the nucleation and growth mechanism originated during this process are not yet comprehensively understood. In this paper, the microstructural characteristics of YBCO films quenched from different growth stages were investigated, upon which a complete nucleation and growth model is established. A micro-Raman and scanning electron microscopy (SEM) coordinated study demonstrates the coexistence of polycrystalline and epitaxial grains at the early stage of nucleation. Combined analysis of transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS) indicates that YBCO epitaxial nucleates by following the Volmer−Weber growth mode. We observed that as the growth process proceeds, the nuclei at the interface have a significant growth advantage over those in the body, thus leading to coalescence of island epitaxial grains via consuming neighboring polycrystalline grains and intermediate phases. Moreover, by establishing a kinetic phase diagram of YBCO film growth, we also found that the optimal process conditions are mainly related to the enhanced transient liquid phase and BaCeO 3 , which are somehow associated with the cross-linkage between the sintering temperature, dwell time, and oxygen partial pressure (pO 2 ) of the sintering atmosphere. Remarkably, a high critical current density (J c ) value of 3.6 MA/cm 2 (77 K, self-field) was obtained in the YBCO film grown on the CeO 2 capped technical substrate deposited under optimized conditions, which is rather comparable with that on the LaAlO 3 single crystal. The angulardependent J c analysis revealed that the anisotropy of the YBCO film is reduced to 3, as estimated by the Blatter scaling approach, which is much smaller than that of the typical defect-free pristine films. This work improves understanding of the nucleation and growth mechanism in the YBCO film deposited on the CeO 2 -buffered technical substrate and facilitates the industrialization development of epitaxial oxide films with superior performance in the future.

No abstract

Due to the high growth rate and environmental‐friendly, fluorine‐free metal‐organic decomposition routes (FF‐MOD) have attracted more attention for growth of high‐quality YBa2Cu3O7‐δ (YBCO) films. Few works have been performed when using technical substrates. In this study, correlation among the sintering process, microstructure, and superconductivity of the YBCO was systematically established on the technical substrates capped with CeO2 layer. We found that the optimal process conditions are mainly related to the enhanced transient liquid phase and BaCeO3. Combined X‐ray diffraction and scanning electron microscopy analyses indicate that high‐quality growth of YBCO film is a trade‐off of two different competition phenomena during sintering: (a) the presence of enhanced transient liquid phase, (b) the formation of BaCeO3 at the interface. The former is beneficial to YBCO epitaxial growth/structure rearrangement, while the latter should be suppressed in view of minimizing YBCO partial decomposition triggered by the interfacial reaction. Moreover, we confirmed that both two aforementioned phenomena are somehow associated with the cross‐linkage between the sintering temperature and pO2 during the YBCO conversion. According to this systemic study, the key parameters are defined to avoid the BaCeO3 formation prior to the YBCO orientation nucleation. Structure and superconductivity of the YBCO film were also investigated. Remarkably, a high Jc value of 3.69 mA/cm2 (77 K, sf) was obtained in the YBCO film grown on the CeO2 technical substrate deposited under optimized deposition conditions, which is rather comparable with that on the LaAlO3 single crystal. TEM cross‐sectional observation reveals that the enhanced Jc (B) properties of the YBCO film are mainly contributed by high density of short stacking faults. This work demonstrates the feasibility of FF‐MOD to fabricate high‐performance YBCO films on the CeO2‐buffered technical substrate.

No abstract

Tuning substrate properties is an effective methodology to modulate the texture development of MgO films deposited by ion beam-assisted deposition (IBAD) process for epitaxial oxide films. Herein, a solution deposition planarization (SDP) technique is employed to deposit Gd-Zr-O layer for engineering surface properties of the flexible metal substrate. The correlation between the Gd-Zr-O thin film microstructure and the IBAD-MgO texture is investigated. The coordinated study on atomic force microscopy (AFM) and reflection high-energy electron diffraction (RHEED) reveal that the grain coarsening during high-temperature sintering negatively influences the texture formation of IBAD-MgO. Moreover, the chemical environment of the atoms on the surface of Gd-Zr-O seed layer also plays a critical role, which is normally overlooked. The X-ray photoelectron spectroscopy (XPS) analysis indicates that the carbon residue and intermediate phase result in the poor texture of the IBAD-MgO. This phenomenon is related to the partial decomposition and synthesis reactions due to the lower sintering temperature or reduced surface to volume ratio. We demonstrate the high-quality texture of IBAD-MgO layer, deposited on mono-coated thick Gd-Zr-O film, by using optimal heat-treatment conditions. The cross-sectional TEM images present the dense Gd-Zr-O film with Gd 2 Zr 2 O 7 nanograins. The multifunctionalities, such as planarization, a barrier layer, and seed layer, of Gd-Zr-O layers are realized in full-stacked CeO 2 /LaMnO 3 /IBAD-MgO/SDP-Gd-Zr-O/C276 samples. This work demonstrates a route for simplifying the architecture of 2G-HTS using Gd-Zr-O layer and explores the effect of the surface properties on texture formation in IBAD-MgO layer. K E Y W O R D S chemical environment of the atoms, coated conductors, Gd-Zr-O amorphous films, ion beam-assisted deposition, solution deposition planarization, surface roughness