Structural and electrical properties of Al-substituted Ba-based Bi-2223 High-Tc superconductor

This study investigates the structural and electrical properties of the Barium-based Bi-2223 high-temperature superconductor system (Bi2-xAlxBa2Ca2Cu3O10+δ) through partial Aluminum substitution (x = 0, 0.1, 0.2). In this study, samples were synthesized via the solid-state reaction method at 860 °C. This research addresses the lattice instability typically induced by the large ionic radius of Barium by employing Aluminum as a “lattice engineering” tool to generate compensatory chemical pressure. X-ray diffraction (XRD) analysis confirmed that the samples crystallized in an orthorhombic structure, with Al-doping significantly enhancing the high-Tc (Bi-2223) phase volume fraction, which reached 76.48% at x = 0.2. Morphological examination using Atomic Force Microscopy (AFM) revealed that cation substitution promotes favorable grain growth, characterized by distinct rhombus-like structures and increased surface roughness. Electrical resistivity measurements demonstrated a remarkable improvement in superconducting properties, with the critical transition temperature (Tc) rising from 105 K in the undoped sample to a maximum of 116 K for x = 0.2. This enhancement is attributed to the internal hydrostatic strain introduced by the smaller Al+3 ions, which stabilizes the crystal lattice, optimizes Cu-O bond lengths, and increases oxygen content (δ), thereby tuning the charge carrier concentration to optimal levels. These findings validate Aluminum substitution as an effective strategy for stabilizing Ba-based cuprates and maximizing their critical temperature.