Quantitative Evaluation of Loss Capability for In Situ Conductive Phase Enhanced Microwave Absorption of High‐Entropy Transition Metal Oxides

Abstract

High-entropy oxides (HEO) with high stability and designability are potential microwave absorbers that serve in harsh environments. However, loss design is critical for the absorption performance of HEO due to its weak intrinsic loss capability. Inadequate loss ability results in considerable secondary reflection. Here, an in situ conductive heterogeneous phase is constructed in (Fe 0.2x Co 0.2 Ni 0.2 Cr 0.2 Mn 0.2 ) 3 O 4 (x = 1-5) using a reductive circumstance, to form a dual-phase composite. Both the ohmic and dielectric loss are enhanced as the conductive phase is introduced, while great impedance matching condition is well maintained. Hence, the composites can achieve substantial absorption across the whole X or Ku band with a thin thickness. Furthermore, key efforts are made to reveal the relationship between the absorbing performance and loss capability of an absorber. The analytical expression of the theoretical threshold of attenuation constant is derived. Based on the statistics of experimental data, the broad feasibility and practicability of the proposed theoretical threshold of attenuation constant are confirmed and discussed. Combined with both the theoretical and experimental studies, the mechanism by which the conductive phase contributes to increased absorption is also disclosed, providing an effective basis for the loss design of broadband microwave absorbers.

Structural Defects in Phase‐Regulated High‐Entropy Oxides toward Superior Microwave Absorption Properties

“…[3a] Dai et al used an in situ reductive strategy to constructed a heterogeneous phase in HE (Fe 0.2x Co 0.2 Ni 0.2 Cr 0.2 Mn 0.2 ) 3 O 4 , to form a dual-phase composite. [15] The composites can achieve substantial absorption almost across the whole X band. However, the exploration of complexphase HE oxides is still in the early stage, and the preparation of complex-phase HE absorbers with stable entropy while ensuring the quantitative regulation of the ratio of each crystalline phase remains a challenging task.…”

“…By enriching the heterogeneous interfaces within ceramics by introducing a second phase, a broader platform can be provided for tuning the properties of absorbing materials. [ 3a,15 ] A novel HE rare earth silicide carbides/oxides (Tm 0.2 Y 0.2 Pr 0.2 Gd 0.2 Dy 0.2 ) 3 Si 2 C 2 /(Tm 0.2 Y 0.2 Pr 0.2 Gd 0.2 Dy 0.2 ) 2 O 3 showed an RL min value of −40.7 dB and EAB achieved 3.4 GHz with a thickness of 2.9 mm. [ 16 ] It was reported that the coexistence of spinel‐type and corundum‐type phases in HE oxide (Fe x CoNiCrMn) m O n presented the enhanced EM wave absorption properties in comparison with single‐phase HE oxides.…”

Catfish Effect Induced by Anion Sequential Doping for Microwave Absorption

“…[1][2][3] Meanwhile, microwave absorption (MA) materials need to be developed to solve the mutual interference of electronic signals. [4,5] Currently, substantial the sp 2 hybrid carbon, thus improving the electronic limiting density and strengthening the conduction loss, while pyridinic N and pyrrolic N located at edge sites mainly involved in dipolar polarization. [20][21][22][23] Not limited to a single element, a system in which multiple elements coexist may produce a synergistic coupling effect of electronic interactions.…”

“…[ 1–3 ] Meanwhile, microwave absorption (MA) materials need to be developed to solve the mutual interference of electronic signals. [ 4,5 ] Currently, substantial progress has been made in MA research, e.g., morphology control, [ 6 ] heterojunction design, [ 7 ] electromagnetic recombination, [ 8 ] and doping engineering. [ 9 ] Among them, doping engineering is the highly attractive strategy developed for tuning intrinsic crystal structure, which exhibits a wider controllable space of electromagnetic response.…”

Structural Engineering Enabled Bimetallic (Ti1‐yNby)2AlC Solid Solution Structure for Efficient Electromagnetic Wave Absorption in Gigahertz

“…demonstrated a Fe‐incorporated of (Fe 0.2 x Co 0.2 Ni 0.2 Cr 0.2 Mn 0.2 ) 3 O 4 , Fe atom as the conductive phase, help to enhance both ohmic loss and dipole polarization. [ 22 ] Gao et al. exhibited a novel Cu/C@MoS 2 solid solutions that can improve EMA property and establish fresh polarization models (various point and face polarization centers), as well as shed new light on the synergistic polarization of different dielectric loss in MoS 2 ‐based solid‐solution structures.…”