| Résumé: | Recently, significant progress has been made in developing high-quality bulk
superconductors using rare earth materials, particularly YBa2Cu3O7-δ (YBCO / Y-
123), for potential applications. However, these materials often face the challenge of
weak link behavior due to defects such as structural inconsistencies, pores, voids, and
non-superconducting phases at the grain boundaries, leading to low critical current
density (Jc). This project aims to understand the complex interactions among
inhomogeneities, non-superconducting phases, and thermodynamic fluctuations of
superconducting parameters during the superconducting transitions. The research
involves incorporating various low concentrations (0.0100 wt.% ≤ x ≤ 0.6000 wt.%)
of chitosan (CHI), CaO and calcium compounds (CaO, CaCO3, and Ca(OH)2)
extracted from chicken eggshells (CaES) into the YBCO matrix through thermal
treatment method annealed under oxygen atmosphere and ambient. XRD results
showed that all specimens crystallised into orthorhombic, Y-123 and nonsuperconducting
phases such as Y-211 and BaCuO2. These additions introduced different trends in grain degradation, spiral growth and nano entities within the YBCO
matrix system. Investigations into the excess conductivity through DC resistivity
measurements of these bulk granular specimens revealed a complete reduction in interlayer
coupling while preserving oxygen content and grain size. Furthermore,
superconducting transition temperatures (Tc-onset, Tc-offset), superconducting transition
width (Tc) and inter-granular current density (Jc(0)) experienced significant
improvements at deficient concentrations (0.0100 wt.%, 0.0375 wt.% and 0.0750
wt.%). The Jc(0) reached peak value at 1.10 × 107 A/m2 for specimen 0.0375 wt.% with
CaO addition, which annealed in oxygen atmosphere, 1.03 × 107 A/m2 for specimen
0.0375 wt.% with CHI addition annealed in ambient, and 9.41 × 106 A/m2 for specimen
0.0100 wt.% with CaES addition annealed in ambient. The excess conductivity of
these granular specimens revealed a dimensional crossover from 2D to 3D fluctuation
as the temperature decreased. This could be attributed to the presence of nonsuperconducting
phases (Y-211 and BaCuO2) exhibiting inhomogeneity, which
functioned as low-resistance grain boundaries and led to an improvement of thermal
fluctuation parameters. It also serves as an effective superconducting connection
between the grains. Incorporation below 0.0375 wt.% proved suitable for achieving
finely scaled lattice defects that can act as effective pinning centres, dominating the
3D regime of thermal fluctuation, reducing flux motion and improving Jc(0). This
project underlines the potential of a sustainable approach involving incorporating lowconcentration
organic polymer (CHI), CaO and Ca compound.
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