The nano-lead advantage: synergizing phase stability and high-Tc performance in Hg-1223 superconductors

Abstract

High-temperature superconducting samples of the nominal composition HgBa2Ca2Cu3-xNano-PbxO8+δ (with x = 0.00, 0.05, 0.10, and 0.15) were synthesized via the solid-state reaction technique to investigate the impact of Nano-lead substitution on phase stability and superconducting properties. X-ray diffraction (XRD) analysis confirmed that all samples crystallized in the tetragonal Hg-1223 phase, identifying a monotonic expansion of the unit cell volume driven by the ionic radius mismatch between the host and dopant cations. Quantitative phase analysis demonstrated a remarkable enhancement in phase purity, with the volume fraction of the high-Tc Hg-1223 phase increasing from 57.10% in the undoped sample to 79.40% at x = 0.15. Additionally, the Size-Strain Plot (SSP) method proved statistically superior to the Scherrer method for crystallite size estimation by effectively decoupling lattice strain. Morphological characterization using Field Emission Scanning Electron Microscopy (FESEM) revealed that Nano-Pb doping significantly promoted microstructural densification and grain connectivity, thereby reducing porosity. Electrical resistivity measurements indicated a non-monotonic behavior in the critical transition temperature (Tc); an initial suppression at x = 0.05 was attributed to electronic disorder and carrier concentration shifts, while higher doping levels restored and enhanced superconductivity. Consequently, the sample with x = 0.15 achieved a maximum Tc of 130.48 K, a result ascribed to the synergistic effects of optimized phase purity and improved inter-grain connectivity.