Structural Core-Shell beyond Chemical Homogeneity in Non-Stoichiometric Cu5FeS4 Nano-Icosahedrons: An in Situ Heating TEM Study

Fabrication of novel direct Z-scheme + isotype heterojunction photocatalyst g-C3N4/TiO2 with peroxymonosulfate (PMS) activation synergy and 2D/0D structure

A novel strategy for fabricating C3N4/TiO2 Z-scheme heterojunctions based on C3N4 isotype heterojunctions is presented. This scheme exploits the structural plasticity of C3N4 to achieve a breakthrough in activity without adding new materials.

Realizing Enhanced Thermoelectric Performance and Hardness in Icosahedral Cu5 FeS4-x Sex with High-Density Twin Boundaries

Bornite (Cu₅ FeS₄ ) is an Earth-abundant, nontoxic thermoelectric material. Herein, twin engineering and Se alloying are combined in order to further improve its thermoelectric performance. Cu₅ FeS_4-x Se_x (0 ≤ x ≤ 0.4) icosahedral nanoparticles, containing high-density twin boundaries, have been synthesized by a colloidal method. Spark plasma sintering retains twin boundaries in the pellets sintered from Cu₅ FeS_4-x Se_x colloidal powders. Thermoelectric property measurement demonstrates that alloying Se increases the carrier concentration, leading to much-improved power factor in Se-substituted Cu₅ FeS₄ , for example, 0.84 mW m^-1 K^-2 at 726 K for Cu₅ FeS_3.6 Se_0.4 ; low lattice thermal conductivity is also achieved, due to intrinsic structural complexity, distorted crystal structure, and existing twin boundaries and point defects. As a result, a maximum zT of 0.75 is attained for Cu₅ FeS_3.6 Se_0.4 at 726 K, which is about 23% higher than that of Cu₅ FeS₄ and compares favorably to that of reported Cu₅ FeS₄ -based materials. In addition, the Cu₅ FeS_4-x Se_x samples containing twin boundaries also obtain improved hardness compared to the ones fabricated by melting-annealing or ball milling. This work demonstrates an effective twin engineering-composition tuning strategy toward enhanced thermoelectric and mechanical properties of Cu₅ FeS₄ -based materials.

Bi and Sn Co-doping Enhanced Thermoelectric Properties of Cu3SbS4 Materials with Excellent Thermal Stability

Cu₃SbS₄-based materials composed of nontoxic, low-cost, and earth-abundant elements potentially exhibit favorable thermoelectric performance. However, some key transport parameters and thermal stability have not been reported. In this work, the effects of Bi and Sn co-doping on thermoelectric properties and the thermal stability of Cu₃SbS₄ were studied by experiment and theoretical validation. Bi and Sn doping can effectively tune the electrical properties and the electronic band structure. The Bi and Sn doping leads to an increased carrier concentration from 6.4 × 10¹⁷ to 7.4 × 10²⁰ cm^-3 and a decreased optical band gap from 0.85 to 0.73 eV. The effective mass was increased from ∼3.0 m_e for Bi-doped samples to ∼4.0 m_e for Bi and Sn co-doped samples. An enhanced power factor of 1398 μW m^-1 K^-2 at 623 K was obtained for Cu₃Sb_1-x-yBi_xSn_yS₄ (x = 0.06, y = 0.09). The measurements of elastic properties exhibited a large Grüneisen parameter (γ ∼2) for Cu₃SbS₄-based materials. Finally, a maximum zT of 0.76 ± 0.02 at 623 K was achieved for Cu₃Sb_1-x-yBi_xSn_yS₄ (x = 0.06, y = 0.05) sample. In addition, Cu₃SbS₄ materials possess excellent thermal stability after thermal treatment in vacuum at 573 K for totally 500 h and dozens of heating-cooling thermal cycles (300-623-300 K). It indicates that Cu₃SbS₄ is a robust alternative for Te-free thermoelectric materials at an intermediate temperature range. This work provides feasible guidance to survey the thermal stability of chalcogenides.