Thermal fluctuation and excess conductivity properties of YBCO-added CHITOSAN, CaO and Ca compound

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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