Shengnan Zhang

Chevrel phases are promising medium‐ to high‐temperature thermoelectrics owing to their structural stability and intrinsically low lattice thermal conductivity, yet prolonged high‐temperature synthesis causes grain coarsening and limits microstructural control. Here, we report an ultrafast solid‐state synthesis strategy for preparing phase‐pure ternary Chevrel phases within 20 min, reducing the reaction time by up to two orders of magnitude. Phase‐evolution analysis and density functional theory calculations suggest a possible formation pathway involving metal‐vapor insertion into metastable Mo ₆ S ₈ intermediates, potentially facilitated by reaction‐induced local overheating. This strategy is successfully extended to multiple sulfide‐ and selenide‐based Chevrel phases. The shortened synthesis process suppresses grain growth and enables microstructure‐mediated transport optimization. As a model system, microstructure‐refined Cu ₂ Mo ₆ S ₈ exhibits suppressed lattice thermal conductivity and a peak zT of 0.40 at 900 K. Further increasing the Cu content to Cu _3.66 Mo ₆ S ₈ introduces enhanced structural disorder and interface‐induced energy filtering, simultaneously improving the Seebeck coefficient and reducing lattice thermal conductivity at elevated temperatures. Consequently, Cu _3.66 Mo ₆ S ₈ achieves a peak zT of 0.44 at 900 K, the highest value reported for ternary sulfide‐based Chevrel phases, together with a high average zT over 300–950 K.

Since its discovery in 2001, magnesium diboride (MgB ₂ ) has attracted significant interest for large-scale superconducting applications due to its high transition temperature (39 K), low material cost, and weak crystallographic anisotropy. This review critically assesses progress and remaining challenges in the industrialization of MgB ₂ superconducting wires, covering material optimization, fabrication techniques, and emerging applications. Key material strategies include precursor powder control, carbon doping, and high-pressure sintering to enhance wire performance. Various fabrication routes are evaluated for their industrial maturity and capability to produce kilometer-length wires with improved current-carrying capacity. Recent application progress in superconducting joints, magnetic resonance imaging systems, superconducting cables, and superconducting magnetic energy storage is also reviewed. Although full-scale commercialization has not yet been realized, recent demonstrations indicate that MgB ₂ technology is transitioning from proof of concept to early-stage industrial adoption. Current technical bottlenecks and future directions are discussed, offering perspectives on the path toward cost-effective, large-scale superconducting applications.

37-filamentary Bi₂Sr₂Ca₂Cu₃O_10+δ (Bi-2223) superconducting tapes were prepared by the powder-in-tube (PIT) technique. Leakage occurring during high-temperature processing is a major issue that degrades both the engineering critical current density (Jₑ) and mechanical properties of Bi-2223 conductors. In this work, the critical silver sheath thickness required to eliminate leakage was systematically investigated by correlating leakage behavior with local sheath thickness in different tapes. The results demonstrate that the leakage can be effectively eliminated when the silver sheath thickness exceeds 38 μm, which is identified as the critical threshold. Furthermore, increasing the wall thickness of the outer Ag alloy tube is shown to be an efficient approach for producing optimized Bi-2223 superconducting tapes. When the wall thickness of the outer Ag-alloy tube is increased from 0.6 mm to 0.8 mm or greater, the silver sheath thickness in the tapes exceeds 42 μm, which was above the critical value required for leakage suppression. These findings provide a practical guideline for reducing leakage in Bi-2223 tapes and offered a viable strategy applicable to other multifilamentary superconducting tapes and wires.

The mechanical response of Bi-2223 multi filamentary superconducting wires during cold drawing directly affects filament integrity and overall performance. A homogenized finite element model based on the mixture theory was established to describe the elastic–plastic behavior of Bi 2223/Ag composite wires. Drawing processes for 37, 55, and 121 filament architectures were analyzed under realistic die–wire contact conditions. The simulations show a pronounced radial stress gradient, with outer filaments carrying higher loads. As the filament number increases, load sharing becomes more uniform and the overall stress concentration decreases. Quantitative analysis of filament distortion indicates that increasing the filament count improves structural uniformity but also enhances the sensitivity to local imperfections. The proposed modeling framework provides a reliable basis for optimizing wire architecture and drawing parameters to improve the mechanical stability and superconducting performance of Bi-2223 wires.

MgB₂ superconducting wires made with internal magnesium diffusion (IMD) process have reached an excellent performance than other routes. However, the incomplete Mg/B reaction has been the core problem of IMD process. In this study, MgB₂/Ni IMD superconducting monofilament wires were prepared using the improved IMD process. By exploring annealing processes during fabrication, we improved the ductility of the wires and ensured the uniform continuity of the central Mg core filaments. The optimal heat treatment process for MgB₂/Ni IMD wires was ascertained by micro structural morphology analysis, phase structure analysis, superconducting property analysis. The study demonstrates that this processing technique leads to a more complete reaction between Mg and B after heat treatment. The critical current density of MgB₂/Ni super-conducting wires was measured at 4.2 K, demonstrating high current-carrying capabilities, particularly at high magnetic fields. This research provides valuable insights for the processing and heat treatment of MgB₂/Ni multi-core superconducting wires in the future.

To optimize the superconducting properties of PbMo₆S₈ (PMS) bulks, we refined the precursor stoichiometry and applied a controlled heat-treatment method—slow ramping, multi-step holds, and a low-vacuum atmosphere—that ensures complete reaction and uniform phase formation in the Pb–Mo–S system. Microstructural analysis, phase-composition characterization, and superconducting performance evaluation were carried out. Results reveal that in this work PMS prepared from elemental Pb, Mo and S powders reaches a sharp superconducting transition at a superconducting transition temperature (T_c) about 14 K and the critical current density (J_c) was 4 × 10⁴ A cm^-2 at 4.2 K, self-field. The enhanced performance is attributed to a synergistic flux-pinning effect. The refined grain structure increases the grain-boundary density, while nanometer-scale lattice distortions and dislocations—whose characteristic size matches the superconducting coherence length ξ ≈ 2 nm—act as additional strong pinning centers. Consequently, point and surface pinning operate concurrently, markedly improving J_c under applied magnetic fields. These findings provide a practical route for fabricating high-performance PMS superconductors through elemental-powder processing.