Bahadir Akkurt

The influence of diffusion‐assisted Co treatment and diffusion–annealing temperature on the structural, mechanical, and superconducting properties of bulk MgB ₂ superconductors is systematically investigated using X‐ray diffraction (XRD), scanning electron microscopy (SEM), Vickers microhardness, semi‐empirical indentation modeling, and temperature‐ and field‐dependent magneto‐resistivity measurements. The six semi‐empirical hardness models, namely Meyer's law (ML), proportional specimen resistance (PSR), modified proportional specimen resistance (MPSR), elastic–plastic deformation (EPD), Hays–Kendall (HK), and indentation‐induced cracking (IIC), are employed to characterize the load‐dependent deformation and hardness response. XRD and SEM analyses reveal a pronounced temperature‐dependent microstructural evolution, with the 700°C treatment producing the largest XRD‐derived crystallite size (27.102 nm), the lowest lattice‐strain and dislocation–density indicators, and a comparatively compact and homogeneous morphology. The reported structural characteristics coincide with the highest Vickers hardness over the entire load range and the most favorable mechanical response within the Co‐treated series. The HK model provides the closest agreement with the experimentally measured load‐independent hardness, whereas the fitted parameters of the different models are interpreted according to their respective physical assumptions rather than regression quality alone. At higher annealing temperatures, increased peak broadening, reduced crystallite size, increased lattice‐strain and dislocation‐density indicators, renewed MgO‐related diffraction features, and greater morphological heterogeneity are accompanied by deterioration of mechanical performance. Magneto‐resistivity measurements under magnetic fields up to 6 T further show a strong dependence of superconducting transport on the diffusion–annealing condition. The evolution of superconducting transition temperatures, transition widths, thermally activated flux flow (TAFF), and activation energy scales indicates that the transport behavior is predominantly influenced by vortex dynamics within the investigated field and temperature ranges. The MgCo‐700 sample exhibits the most favorable superconducting response, with zero‐field onset and offset transition temperatures of 38.65 and 38.09 K, respectively, a transition width increasing from 0.56 K at self‐field to 1.40 K, and an activation energy scale decreasing from 8908 ± 321 K at zero field to 2820 K ± 195 K at 6 T. The observed results indicate comparatively enhanced resistance to thermally activated vortex motion and improved magnetic‐field tolerance at the intermediate annealing condition. Consequently, the combined structural, mechanical, and magneto‐transport results demonstrate that 700°C provides the most favorable balance between crystallographic state, morphological consolidation, deformation resistance, and superconducting transport stability within the investigated Co‐diffused MgB ₂ system. The findings highlight diffusion–annealing temperature as an effective processing variable for tailoring the multifunctional performance of MgB ₂ superconductors while emphasizing the importance of avoiding excessive thermal treatment.

This study investigates the synthesis–structure–property relationships in functional electronic materials by coupling structural evolution with electrical and superconducting performance. On this basis, the role of Dy ³⁺ substitution (0.00 ≤ x ≤ 0.10) on the structural, flux pinning ability, electrical, and superconducting characteristics of Bi _2.1−x Dy _x Sr _2.0 Ca _1.1 Cu _2.0 O _y (Bi-2212) ceramics, synthesized via the conventional solid-state reaction method, is systematically examined. X-ray diffraction (XRD), electrical resistivity (ρ–T), bulk density, and current–voltage (I–V) measurements reveal that an optimum substitution level of x = 0.01 yields superior performance. At this composition, microstructural refinement enhances grain connectivity, lattice coherence, crystallinity, and nucleation-pinning centers, leading to improved superconducting transitions (onset superconductive temperatures ≈ 85.0 K and offset ≈ 80.3 K), larger crystallite size, and enhanced texture quality. Increased carrier concentration and stabilized Bi-O and Cu-O planes promote electron-phonon interactions, supporting stronger superconducting cluster formation. Correspondingly, the critical current density reaches a maximum of 67 A/cm ² , attributed to reinforced flux pinning and vortex coupling. Multi-criteria decision analysis (MCDA) further confirms the optimized sample (Bi _2.09 Dy _0.01 Sr _2.0 Ca _1.1 Cu _2.0 O _y ) achieves the highest normalized performance score (~ 0.90), demonstrating that Dy substitution at x = 0.01 simultaneously improves structural integrity, electrical conductivity, and superconducting efficiency. These results establish Dy doping as a viable pathway to enhance the functional reliability of Bi-2212 ceramics, advancing their potential for electronic and energy-related applications.

This study investigates the effect of aliovalent Co/Cu replacement and preparation method on fundamental mechanical performance features of YBa₂Cu_3−xCo_xO_7−δ (Y-123) ceramic system depending on the crack propagation mechanism by Vickers hardness measurements (H_v) and mechanical investigation models for the first time. All the findings are verified by the scanning electron microscopy (SEM) examinations. Besides, the electron-dispersive X-ray (EDX) technique verifies the successful substitution mechanism. Besides, the Vickers hardness parameters improve systematically with the increment in the Co/Cu partial substitution (serving as a barrier) level due to formation of operable slip systems, ionic bond formations, and decrement of stress-amplified strain fields. Moreover, the Y-123 ceramic produced by solid-state reaction method and molecular weight of 0.20% presents the densest and smoothest surface morphology with the largest particle distributions and well-linked cobblestone-like grains. On the other hand, the Y-123 ceramic compounds produced by the sol–gel method are more sensitive and responsive to the indentation test loads. All the findings are wholly supported by the mechanical performance properties, including the shear modulus, resilience, and degree of granularity. Furthermore, the mechanical models indicate that every compound prepared exhibits the untypical reverse indentation size effect (RISE). Additionally, the modeling studies display that the induced cracking (IIC) approach is found to be the most appropriate method to examine true Vickers hardness parameters in the plateau limit regions. All in all, this comprehensive study reports efficiently exploiting the process–structure–property relationships in Y-123 ceramic material design for physical science and mechanical application fields using the aliovalent partial substitution and preparation condition.