Abstract
Considering the emergence of severe electromagnetic interference problems, it is vital to develop electromagnetic (EM) wave absorbing materials with high dielectric, magnetic loss and optimized impedance matching. However, realizing the synergistic dielectric and magnetic losses in a single phase material is still a challenge. Herein, high entropy (HE) rare earth hexaborides (REB6) powders with coupling of dielectric and magnetic losses were designed and successfully synthesized through a facial one-step boron carbide reduction method, and the effects of high entropy borates intermedia phases on the EM wave absorption properties were investigated. Five HE REB6 ceramics including (Ce0.2Y0.2Sm0.2Er0.2Yb0.2)B6, (Ce0.2Eu0.2Sm0.2Er0.2Yb0.2)B6, (Ce0.2Y0.2Eu0.2Er0.2Yb0.2)B6, (Ce0.2Y0.2Sm0.2 Eu0.2Yb0.2)B6, and (Nd0.2Y0.2Sm0.2Eu0.2 Yb0.2)B6 possess CsCl-type cubic crystal structure, and their theoretical densities range from 4.84 to 5.25 g/cm3. (Ce0.2Y0.2Sm0.2Er0.2 Yb0.2)B6 powders with the average particle size of 1.86 µm were found to possess the best EM wave absorption properties among these hexaborides. The RLmin value of (Ce0.2Y0.2Sm0.2Er0.2Yb0.2)B6 reaches −33.4 dB at 11.5 GHz at thickness of 2 mm; meanwhile, the optimized effective absorption bandwidth (EAB) is 3.9 GHz from 13.6 to 17.5 GHz with a thickness of 1.5 mm. The introduction of HE REBO3 (RE = Ce, Y, Sm, Eu, Er, Yb) as intermediate phase will give rise to the mismatching impedance, which will further lead to the reduction of reflection loss. Intriguingly, the HEREB6/HEREBO3 still possess wide effective absorption bandwidth of 4.1 GHz with the relative low thickness of 1.7 mm. Considering the better stability, low density, and good EM wave absorption properties, HE REB6 ceramics are promising as a new type of EM wave absorbing materials.
Highlights
With the electromagnetic (EM) wave as an important carrier of information exchange penetrating into all aspects in human life, it is critical to develop high performance EM wave absorbing materials to eliminate the adverse effects of EM wave, such as the electromagnetic interference and microwave pollution [1,2,3]
In order to study the influence of intermediate phases, i.e., high-entropy rare-earth borates (HE REBO3) on the EM wave absorption performance of high entropy (HE) REB6, the pellets were heated to 1600 °C and kept for 1 h in Ar atmosphere to obtain HE REB6/HE REBO3 composites
As for the intriguing magnetism found in REB6, the magnetic ordering might be attributed to an indirect exchange of the RKKY type via conduction electrons donated from trivalent rare-earth ions or impurities [51,52]
Summary
With the electromagnetic (EM) wave as an important carrier of information exchange penetrating into all aspects in human life, it is critical to develop high performance EM wave absorbing materials to eliminate the adverse effects of EM wave, such as the electromagnetic interference and microwave pollution [1,2,3]. Under increasingly complex serving environment, EM wave absorbing materials are required to possess the following properties: (1) strong absorption, broad efficient absorption bandwidth, and optimized impedance matching; (2) lightweight, good mechanical property, and favorable high-temperature stability; (3) resistance to corrosion and oxidation; (4) easy fabrication and cost-efficient [3,4,5]. Considering the conductivity and magnetism of rare-earth (RE) hexaborides (REB6), it is expected that lightweight REB6 ceramics possess promising EM wave absorption properties. Combining excellent high-temperature property, good electrical conductivity and magnetic property, REB6 are expected to be a new type of promising EM wave absorbing materials. The aims of this work are to design and synthesize HE REB6 and to explore the EM wave absorption properties of HE REB6 To achieve these goals, five high-entropy rare-earth hexaborides (Ce0.2Y0.2Sm0.2Er0.2Yb0.2)B6, (Ce0.2Eu0.2Sm0.2Er0.2Yb0.2)B6, (Ce0.2Y0.2Eu0.2Er0.2Yb0.2)B6, (Ce0.2Y0.2Sm0.2Eu0.2Yb0.2)B6, and The formation of HE REB6 could lead to further improvement of the comprehensive properties including mechanical property, thermal property, and EM wave absorption property
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