Abstract:Microwave absorbing materials have attracted much attention in solving electromagnetic interference and pollution problems. Hierarchical cobalt selenides have been obtained through a facile selenization annealing process. The as-prepared samples exhibit distinct reflection losses (RL) and frequency responses via tailoring their crystalline configurations, with excellent absorption in Ku, X, or C band. All the samples show RL greater than or near to -50 dB with effective bandwidths more than 4 GHz, indicating t… Show more
“…Remarkably, both of C‐2:5 and P‐2:5 exhibit excellent advantage compared with others. Surprisingly, C‐2:5 holds the best EMW absorption performance accompanied with an EAB as large as 9.25 GHz (8.75–18 GHz) at 2.42 mm (Figure 3o), overwhelmingly surpassing all advanced metal sulfides/selenides absorbents reported previously, [ 7,16,29–38 ] as collected in Figure a and Table S9 (Supporting Information). This EMW absorption performance is much attractive because it is still a significant challenge to cover X ‐band (8–12 GHz) and Ku ‐band (12–18 GHz) simultaneously with a thin matching thickness.…”
Vacancy engineering is an attractive approach to modulate the electronic structure of transition metal chalcogens. However, illustrating how anion vacancy can be engineered to tailor their electromagnetic (EM) parameters and electromagnetic wave (EMW) absorption, based on clear vacancy concentrations and/or various anion vacancies rather than semiempirical rules, is currently lacking but significantly desired. An anion-doping-induced vacancy engineering is pioneered, where the selective oxidation process upgrades the transformation from Co-based precursor to S-doped CoSe 2 (System II) instead of Se-doped CoS 2 (System I) in the subsequent sulfuration/selenization, which results in vacancy level improvement and coexistence of sulfur vacancies (V S ) and selenium vacancy (V Se ). Thanks to the boosted dielectric polarization loss provided by the comparable coexistence of sulfur/selenium vacancies (V S /V Se = 0.52), S-doped CoSe 2 harvests a broad bandwidth of 9.25 GHz (8.75-18.00 GHz) at 2.42 mm. This feature almost simultaneously achieves 100% coverage for X-, and Ku-bands, outperforming all reported metal sulfides/selenides until now. This work establishes a clear correlation between vacancy concentrations/various anion vacancies and EMW dissipation ability, offering valuable insights for designing advanced EMW absorbing materials.
“…Remarkably, both of C‐2:5 and P‐2:5 exhibit excellent advantage compared with others. Surprisingly, C‐2:5 holds the best EMW absorption performance accompanied with an EAB as large as 9.25 GHz (8.75–18 GHz) at 2.42 mm (Figure 3o), overwhelmingly surpassing all advanced metal sulfides/selenides absorbents reported previously, [ 7,16,29–38 ] as collected in Figure a and Table S9 (Supporting Information). This EMW absorption performance is much attractive because it is still a significant challenge to cover X ‐band (8–12 GHz) and Ku ‐band (12–18 GHz) simultaneously with a thin matching thickness.…”
Vacancy engineering is an attractive approach to modulate the electronic structure of transition metal chalcogens. However, illustrating how anion vacancy can be engineered to tailor their electromagnetic (EM) parameters and electromagnetic wave (EMW) absorption, based on clear vacancy concentrations and/or various anion vacancies rather than semiempirical rules, is currently lacking but significantly desired. An anion-doping-induced vacancy engineering is pioneered, where the selective oxidation process upgrades the transformation from Co-based precursor to S-doped CoSe 2 (System II) instead of Se-doped CoS 2 (System I) in the subsequent sulfuration/selenization, which results in vacancy level improvement and coexistence of sulfur vacancies (V S ) and selenium vacancy (V Se ). Thanks to the boosted dielectric polarization loss provided by the comparable coexistence of sulfur/selenium vacancies (V S /V Se = 0.52), S-doped CoSe 2 harvests a broad bandwidth of 9.25 GHz (8.75-18.00 GHz) at 2.42 mm. This feature almost simultaneously achieves 100% coverage for X-, and Ku-bands, outperforming all reported metal sulfides/selenides until now. This work establishes a clear correlation between vacancy concentrations/various anion vacancies and EMW dissipation ability, offering valuable insights for designing advanced EMW absorbing materials.
“…With regard to polarization relaxation, interfacial polarization and dipole polarization are usually considered in microwave frequency range. 38 According to Debye relaxation theory, the plot of 3 0 -3 00 is a single semicircle (Cole-Cole semicircle) and each semicircle stands for a Debye relaxation process. 39 As shown in Fig.…”
“…We can artificially adjust electromagnetic parameters ( ɛ and μ ) to improve the impedance matching. The EMW attenuation ability means the loss capacity of the EMW which enters into the interior of MAMs [ 24 , 54 , 55 ]. Fig.…”
Section: Theories Of Microwave Absorptionmentioning
The development of microwave absorption materials (MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human’s health. And MAMs are also used in radar stealth for protecting the weapons from being detected. Many nanomaterials were studied as MAMs, but not all of them have the satisfactory performance. Recently, metal–organic frameworks (MOFs) have attracted tremendous attention owing to their tunable chemical structures, diverse properties, large specific surface area and uniform pore distribution. MOF can transform to porous carbon (PC) which is decorated with metal species at appropriate pyrolysis temperature. However, the loss mechanism of pure MOF-derived PC is often relatively simple. In order to further improve the MA performance, the MOFs coupled with other loss materials are a widely studied method. In this review, we summarize the theories of MA, the progress of different MOF-derived PC‑based MAMs, tunable chemical structures incorporated with dielectric loss or magnetic loss materials. The different MA performance and mechanisms are discussed in detail. Finally, the shortcomings, challenges and perspectives of MOF-derived PC‑based MAMs are also presented. We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.
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