Design principles for high-performance Bi-2212 superconducting ceramics via Nd/Bi substitution: Combined theoretical and experimental perspectives

This study presents a combined experimental and density functional theory (DFT) investigation of the effects of partial Nd/Bi substitution (0.00≤x≤0.10) on the structural, electronic, and superconducting properties of Bi 2.0-x Nd x Sr 2.0 Ca 1.0 Cu 2.0 O y (Bi-2212) ceramic systems synthesized by conventional solid-state reaction method for the first time. DFT calculations demonstrate that Nd substitution predominantly influences superconducting behavior through lattice distortion, interlayer strain redistribution, and reorganization of chemical bonding within the Bi–O charge-reservoir layers, rather than via direct electronic doping. These theoretical predictions are fully supported by experimental results. X-ray diffraction reveals that the optimum composition (x = 0.01) exhibits enhanced crystallinity, the highest Bi-2223 phase fraction (21.44%), an enlarged c-axis parameter (32.62 Å), and the largest crystallite size (64.4 nm), while higher Nd contents induce phase instability and secondary-phase formation. Electrical transport measurements show that the x = 0.01 Nd/Bi replaced sample displays the strongest metallic behavior, highest carrier delocalization, and superior superconducting performance, with transition temperatures (onset = 85.54 K and offset = 81.96 K), the lowest resistivity parameters (ρ res =0.54 mΩ.cm, ρ 87 K = 3.29 mΩ.cm, and ρ 300 K = 13.84 mΩ.cm), and a transport critical current density of 71 A.cm −2 at 77 K, attributed to improved grain connectivity and enhanced flux pinning. For x ≥ 0.05, increasing lattice strain and grain-boundary disorder lead to systematic degradation of phase purity, microstructure, and superconducting performance properties. To sum up, the results establish x = 0.01 as an optimum Nd/Bi substitution level, where structural coherence, interlayer coupling, carrier transport, and vortex pinning are simultaneously maximized, providing clear mechanistic vision and practical guidance for optimizing high-performance Bi-based superconducting ceramics.