High-purity, nano-sized (Ti 0.2 Zr 0.2 Nb 0.2 Mo 0.2 Hf 0.2 )B 2 (TZNMH) diboride powders were successfully synthesized via a combined flocculation precipitation and boro/carbothermal reduction method. Then, the solid solution formation, thermal radiation performance and mechanical properties of TZNMH were investigated. It is found that high entropy effect endows TZNMH ceramic with outstanding near-blackbody radiation performance in the UV-Vis-NIR region, with a thermal emissivity ≥ 95%. This is because high entropy induces robust intraband transition. A dense and single-phase TZNMH ceramic was obtained by spark plasma sintering with high hardness (HV 0.1 =31.6 GPa) which remained above 30 GPa even after 60 h exposure at 1800 °C in Ar environment. This high hardness of TZNMH ceramic is believed to arise from the strong hybridization between metals and boron, as revealed by density functional theory calculations. This study demonstrates that high-entropy boride ceramics can be used as ideal high-temperature structural component with high thermal emissivity.
The dielectric performance of BaTiO 3 -based ceramic capacitors must be improved for further miniaturization and integration of energy storage devices. This study combines two optimization strategies, the grain refinement and high-entropy effect, to design BaTiO 3 -based high-entropy nanocrystalline ceramics: Ba(Ti 0.2 Zr 0.2 Nb 0.2 Y 0.2 Sn 0.2 )O 3 (HEO1) and Ba(Ti 0.2 Zr 0.2 Nb 0.2 Yb 0.2 Hf 0.2 )O 3 (HEO2). These ceramics were synthesized using fast hot-pressing sintering (FHPS), yielding HEO1-FHPS and HEO2-FHPS samples, both of which exhibit a pure perovskite structure, similar to that of samples fabricated via conventional solid-state sintering (CS), namely HEO1-CS and HEO2-CS. The relative densities of the HEO1-FHPS (96.18 %) and HEO2-FHPS (98.34 %) samples are higher than those of HEO1-CS (95.47 %) and HEO2-CS (95.40 %). In addition, the grain sizes of HEO1-FHPS (0.092 μm) and HEO2-FHPS (0.084 μm) are notably smaller than those of HEO1-CS (2.48 μm) and HEO2-CS (2.91 μm). The high relative density and small grain size of HEO1 and HEO2 improve their maximum permittivity, increase the Curie temperature and enhance dielectric stability. Furthermore, compared with HEO1-CS and HEO2-CS, HEO1-FHPS and HEO2-FHPS exhibit higher critical electric field strengths (359 and 389 kV/cm), greater recoverable energy densities (0.40 and 0.88 J/cm 3 ) and improved energy storage efficiencies (69.6 % and 70.4 %). These findings provide a promising approach for developing BaTiO 3 -based ceramics with enhanced dielectric performance.
A promising strategy involving the synergetic effects of the high-entropy engineering and interface architectures has been proposed to realize the thermal stability of nanocrystalline alloys. A bulk dual-phase nanocrystalline (DPNC-) AlCoCuNi medium-entropy alloy was prepared by mechanical alloying (MA) and spark plasma sintering (SPS) process. These DPNC structures include Cu-rich and AlCoNi-rich nanocrystallines (NCs) with an average grain size of 46 nm. This DPNC-AlCoCuNi material could maintain the nanostructures as well as a high hardness of about 580 HV even after annealing at 900 °C for 50 h. The extremely high thermal stability has been attributed to the extensive thermal-stabled low-energy phase boundaries, low-angle grain boundaries, the high-entropy and sluggish diffusion effects.
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