Supersaturation-driven defect engineering for enhanced flux pinning in FF-MOD YBCO films via yttrium stoichiometry control

Supersaturation serves as the primary thermodynamic driving force for nucleation, governing
the crystallographic orientation and microstructural evolution of superconducting films. In this
study, we investigated the impact of the yttrium stoichiometry (x = 0.8, 1.0, 1.2) of YxBa2Cu3O7-δ
films grown via fluorine-free metal-organic deposition. By tuning the yttrium content, we effectively
modulated the transient liquid-phase supersaturation, driving a fundamental transition in
the defect architecture and vortex pinning dynamics. The Y-deficient film (Y0.8BCO), grown under
lower supersaturation, lacks a competing dense 3D defect network. Consequently, its microstructural
landscape is dominated by localized planar stacking faults, which provide robust 2D correlated
pinning and sustain a broader vortex trapping angle (θT). Conversely, high supersaturation
in the Y-rich film (Y1.2BCO) generates a dense 3D network of isotropic defects. These fine-scale
disorders dimensionally match a reduced in-plane coherence length (ξab), acting as efficient core
pinning centers that enhance the self-field critical current density (Jc) to 2.0 MA cm−2 at 77 K.
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However, a crucial high-field trade-off emerges: under magnetic fields (>2.7 T), excessive lattice
disorder depresses local superconducting properties, rendering the pristine stoichiometric YBCO
film more robust. Ultimately, balancing the transition between 2D planar and 3D isotropic pinning
regimes via stoichiometry-driven supersaturation engineering provides an effective strategy
for optimizing the in-field performance of REBCO coated conductors.