The high-pressure effect can effectively regulate the bandgap width of thermoelectric materials, thus optimizing the material properties. In this study, the high temperature and high pressure (HPHT) technique was employed to synthesize In-filled, Te/S double-substituted skutterudite-based thermoelectric materials. The effects of synthesis pressures ranging from 2.0 to 3.5 GPa on their phase structure, microstructure, and thermoelectric properties were systematically investigated. XRD and EDS analyses confirm the phase-pure synthesis of In 0.05 Co 4 Sb 11.3 Te 0.6 S 0.1 . The experimental results combined with first-principles calculations indicate that the pressure-induced bandgap widens from 0.245 eV at 2.0 GPa to 0.270 eV at 3.0 GPa, resulting in not only an exponential decay of the conductivity but also a significant increase in the absolute value of the Seebeck coefficient. The analysis based on the Callaway model demonstrates that introducing In, Te, and S elements strengthens grain boundaries, increases point defects, and enhances resonance scattering, thereby effectively reducing lattice thermal conductivity. At 773 K, the 3.0 GPa sample exhibits the lowest thermal conductivity of 1.56 Wm −1 K −1 and a maximum zT value of 1.20, representing a 40.18 % increase over that of the sample synthesized at 2.0 GPa and an 11.02 % increase over that of the Co 4 Sb 11.3 Te 0.6 S 0.1 sample. In addition, the sample synthesized at 3.5 GPa demonstrates excellent mechanical performance, exhibiting a Vickers hardness of 11.12 GPa. New strategies have been provided for the development of materials with both high thermoelectric and mechanical properties.
The ZrCo alloy, considered an ideal candidate material for hydrogen (or its isotope) storage to replace uranium in the ITER, faces challenges due to its susceptibility to hydrogen-induced disproportionation, which leads to a diminished cycling life. To address this, we investigated the substitution of V and Cr for Zr and Co. Our study reveals that this substitution not only refines the grain size and expands the lattice constant but also significantly enhances the kinetics of hydrogen absorption. Notably, the Zr 0.95 V 0.05 Co 0.85 Cr 0.15 alloy demonstrates a remarkable 98.8 % reduction in the time required to absorb 90 % of its full capacity compared to ZrCo. This alloy also exhibits superior isotope effects under H 2 and D 2 environments, along with lower enthalpy and entropy for dehydrogenation, contributing to a reduced dehydrogenation temperature and enhanced resistance to disproportionation. After 50 cycles of hydrogen absorption and desorption, the hydrogen storage capacity of Zr 0.95 V 0.05 Co 0.85 Cr 0.15 alloys decreases by only 5.7 %, significantly outperforming other reference samples and demonstrating its exceptional anti-disproportionation capability. These results indicate that the Zr 0.95 V 0.05 Co 0.85 Cr 0.15 alloy exhibits the best resistance to hydrogen-induced disproportionation. Moreover, post-50 cycling analysis confirms that the phase of the alloy is still dominated by the ZrCo phase, indicating its excellent structural stability. Our findings offer valuable insights into optimizing ZrCo-based alloys for enhanced hydrogen storage performance and cycling stability, providing potential references for advancements in hydrogen isotope storage materials design.
Jun Cao,Chengsheng Wang,Zechao Xu,Kelan Yan,Liming Shen,Zheng Huang,Lingjie Zhang,Runhua Fan,Ningzhong Bao
Metamaterials exhibiting simultaneous negative permittivity (ε < 0) and negative permeability (μ < 0) offer exceptional electromagnetic properties, enabling advanced applications such as subwavelength imaging, wireless power transfer, and advanced antenna systems. Chromium-based selenium spinel composites have emerged as promising candidates for random double-negative metamaterials (DNMs), although achieving tunable and desired double-negative characteristics remains challenging. Here, CoCr2Se4, distinguished by high magnetic spin resonance in high-frequency fields and low conductivity, was selected to modulate the electromagnetic properties of CuCr2Se4-based composites. A series of (1 − x)CuCr2Se4·xCoCr2Se4 samples were synthesized via a solid-state reaction. Double-negative properties were achieved in the MHz frequency ranges, specifically within 841–1000 MHz for x = 0.2, 638–1000 MHz for x = 0.4, and 484–1000 MHz for x = 0.6. The negative permittivity arises from the plasma oscillations of delocalized carriers, well described by the Drude model. Meanwhile, negative permeability is explained through the suppression of eddy currents–due to the low conductivity of CoCr2Se4-which mitigates skin-depth limitations and enhances magnetic resonance. This composite design not only reduces electromagnetic attenuation but also improves magnetic responsiveness under alternating fields. By clarifying the selection rationale for metallic ferromagnetic spinel composites, this work enhances the theoretical understanding and tuning mechanisms of negative ε and μ. It thereby broadens the scope of metamaterial research and facilitates the development of single-phase double-negative materials, especially for low-frequency near-field applications.
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