Three sets of MXene(Ti_(3)C_(2)T_(x))@nano-Fe_(1)Co_(0.8)Ni_(1)composites with 15,45,and 90 mg MXene were prepared by in-situ liquid-phase deposition to effectively investigate the impact of the relationship between M...Three sets of MXene(Ti_(3)C_(2)T_(x))@nano-Fe_(1)Co_(0.8)Ni_(1)composites with 15,45,and 90 mg MXene were prepared by in-situ liquid-phase deposition to effectively investigate the impact of the relationship between MXene(Ti_(3)C_(2)T_(x))and nano-Fe_(1)Co_(0.8)Ni_(1)magnetic particles on the electromagnetic absorption properties of the composites.The microstructure,static magnetic properties,and electromag-netic absorption performance of these composites were studied.Results indicate that the MXene@nano-Fe_(1)Co_(0.8)Ni_(1)composites were primarily composed of face-centered cubic crystal structure particles and MXene,with spherical Fe_(1)Co_(0.8)Ni_(1)particles uniformly distrib-uted on the surface of the multilayered MXene.The alloy particles had an average particle size of approximately 100 nm and exhibited good dispersion without noticeable particle aggregation.With the increase in MXene content,the specific saturation magnetic and coer-civity of the composite initially decreased and then increased,displaying typical soft magnetic properties.Compared with those of the Fe_(1)Co_(0.8)Ni_(1)magnetic alloy particles alone,MXene addition caused an increasing trend in the real and imaginary parts of the dielectric constant of the composite.Meanwhile,the real and imaginary parts of the magnetic permeability exhibit decreasing trend.With the in-crease in MXene addition,the material attenuation constant increased and the impedance matching decreased.The minimum reflection loss increased,and the maximum effective absorption bandwidth decreased.When the MXene addition was 90 mg,the composite exhib-ited a minimum reflection loss of-46.9 dB with a sample thickness of 1.1 mm and a maximum effective absorption bandwidth of 3.60 GHz with a sample thickness of 1.0 mm.The effective absorption bandwidth of the composites and their corresponding thicknesses showed a decreasing trend with the increase in MXene addition,reducing by 50%from 1.5 mm without MXene addition to 1 mm with 90 mg of MXene addition.展开更多
Cobalt nickel bimetallic oxides(NiCo_(2)O_(4))have received numerous attentions in terms of their controllable morphology,high temperature,corrosion resistance and strong electromagnetic wave(EMW)absorption capability...Cobalt nickel bimetallic oxides(NiCo_(2)O_(4))have received numerous attentions in terms of their controllable morphology,high temperature,corrosion resistance and strong electromagnetic wave(EMW)absorption capability.However,broadening the absorption bandwidth is still a huge challenge for NiCo_(2)O_(4)-based absorbers.Herein,the unique NiCo_(2)O_(4)@C core-shell microcubes with hollow structures were fabricated via a facile sacrificial template strategy.The concentration of oxygen vacancies and morphologies of the three-dimensional(3D)cubic hollow core-shell NiCo_(2)O_(4)@C framework were effectively optimized by adjusting the calcination temperature.The specially designed 3D framework structure facilitated the multiple reflections of incident electromagnetic waves and provided rich interfaces between multiple components,generating significant interfacial polarization losses.Dipole polarizations induced by oxygen vacancies could further enhance the attenuation ability for the incident EM waves.The optimized NiCo_(2)O_(4)@C hollow microcubes exhibit superior EMW absorption capability with minimum RL(RLmin)of-84.45 dB at 8.4 GHz for the thickness of 3.0 mm.Moreover,ultrabroad effective absorption bandwidth(EAB)as large as 12.48 GHz(5.52-18 GHz)is obtained.This work is believed to illuminate the path to synthesis of high-performance cobalt nickel bimetallic oxides for EMW absorbers with excellent EMW absorption capability,especially in broadening effective absorption bandwidth.展开更多
The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-perfo...The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-performance microwave absorbing material.In this paper,Y_(2)Co_(17)alloy was prepared by a reduction-diffusion method,and its micropowder was prepared as polyurethane(PU)based composite absorbing materials(Y_(2)Co_(17)/PU composites).The microwave properties of composites with different volume fractions were calculated.The composites showed outstanding absorption characteristics in the range of 20-30 vol%,and the minimum reflection loss(RL)was less than-50 d B.When the volume fraction was25%,the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm,and the Ku-band at a thickness of1.08 mm.The absorption mechanism was analyzed by the interface reflection model.The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses.The effective absorption bandwidth values were in good agreement with the theoretical expectation.展开更多
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 st...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.展开更多
To solve the electromagnetic pollution,herein,a CoFe_(2)O_(4)/C/PANI composite was developed by a green route,which was constructed with spinel of metal oxide,graphitized carbon and conductive polymer composites.Benef...To solve the electromagnetic pollution,herein,a CoFe_(2)O_(4)/C/PANI composite was developed by a green route,which was constructed with spinel of metal oxide,graphitized carbon and conductive polymer composites.Benefiting from the designable interfaces and increased dipoles,the microwave dielectric response capability can be boosted significantly and resulted in the enhanced microwave absorbing performance.As revealed by the reflection loss curve,the minimum reflection loss(RLmin) reached-51.81 dB at 12.4 GHz under a matched thickness of 2.57 mm.At 2.5 mm,the effective absorbing band covered 8.88 GHz,suggesting the desirable wideband feature.In our case,the method of utilization of a novel green way to fabricate multiple-component EM absorber can be a promising candidate for high-performance EM absorber.展开更多
Traditional ferrites are of poor electromagnetic wave(EMW) absorption while doping rare earth elements(REEs) can greatly enhance their permeability to improve the EMW loss performance.In this study,Co-Zn ferrite nanop...Traditional ferrites are of poor electromagnetic wave(EMW) absorption while doping rare earth elements(REEs) can greatly enhance their permeability to improve the EMW loss performance.In this study,Co-Zn ferrite nanoparticles doped with various amounts of REEs(Gd^(3+),Nd^(3+)and Pr^(3+)) were synthesized by a hydrothermal method,and their particle morphology and an EMW absorption performance were characterized by using transmission electron microscopy(TEM) and a Vector network analyzer(VNA).The results show that the initial spherical Co-Zn ferrite nanoparticles present an irregular quadrilateral structure after Gd^(3+)doping,and the average particle size of Co_(0.5)Zn_(0.5-x)Gd_(x)Fe_(2) O_(4) increases from 26 to 50 nm with x increasing from 0 to 0.35.At x of 0.25,the reflectivity absorbance achieves-27.94 dB at 18 GHz with the effective absorption bandwidth(EAB) of 4.08 GHz at a sample thickness of 2.5 mm.When Nd^(3+)doping amount reaches x=0.3,the minimum reflection loss(RL)is-25.63 dB at 18 GHz and EAB is 3.91 GHz.Doping Pr^(3+)(x=0.25) in the sample broadens EAB,and the minimum RL is-16.1 dB at 16.81 GHz and EAB is 7.31 GHz.This study shows that the magnetic moment produced by doping REES can form magnetic domains,which affects the incident EMW and improves the magnetic loss.It is expected that REEs-doped Co-Zn ferrite nanoparticles can be used as efficient electromagnetic shielding materials in aerospace.展开更多
Hollow engineering is considered to be an essential subfield in promoting electromagnetic(EM)wave absorption intensity and realizing lightweight characteristics.However,the enhancement of the effective absorption band...Hollow engineering is considered to be an essential subfield in promoting electromagnetic(EM)wave absorption intensity and realizing lightweight characteristics.However,the enhancement of the effective absorption bandwidth(EAB)still faces considerable challenges.Herein,hollow carbon nanocages with CoFe_(2)Se_(4)quantum dots(HCNs@CoFe_(2)Se_(4)-QDs)with superior EM wave absorption intensity and ultra broadband EAB are produced by using tightly arranged SiO_(2)spheres as hard-template materials.Specifically,the removal of SiO_(2)templates inevitably results in the formation of a hollow cavity,which is favorable for optimizing impedance matching and increasing the absorption intensity.In addition,the incorporation of selenium powder effectively increases the number of heterogeneous interfaces by forming CoFe_(2)Se_(4)quantum dots(QDs)during the pyrolysis process,leading to strengthened interfacial polarization and ultra broadband EAB.As a result,superior EM wave attenuation with a minimum reflection loss(RL)of−67.6 dB and an EAB of 11.4 GHz is achieved with only a 20 wt%filler ratio.This design concept of hollow engineering with magnetic QDs provides inspiration for optimizing the EM wave absorption intensity and simultaneously promoting the absorption bandwidth.展开更多
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,...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,(Ce0.2Hu0.2Sm0.2Er0.2Yb0.2)B6,(Ce0.2Y0.2Eu0.2Er0.2Yb0.2)B6,(Ce0.2Ya2Sm0.2Eu0.2Yb0.2)B6,and(Nd0.2Y0.2Sm0.2Eu0.2Yb0.2)B6 possess CsCl-type cubic crystal structure,and their theoretical densities range from 4.84 to 5.25 g/cm^(3).(Ce02Y0.2Sm0.2Er0.2Yb02)B6 powders with the average particle size of 1.86 jim 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 REB03(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/HEREB03 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.展开更多
Nanocomposites with heterogeneous structures and magneto-electric synergistic losses have broad prospects for improving electromagnetic wave(EMW)absorption performance.In this study,we synthesized Co_(2)NiO_(4)@MnCo_(...Nanocomposites with heterogeneous structures and magneto-electric synergistic losses have broad prospects for improving electromagnetic wave(EMW)absorption performance.In this study,we synthesized Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles with abundant hetero-interfaces and multiple magnetoelectric loss mechanisms by a facile hydrothermal method.The excess 0.5 oxygen atoms in MnCo_(2)O_(4.5) produce more vacancies and contribute to the enhancement of electrical conductivity.Sequential nanoneedle clusters facilitate multiple reflections and absorption of EMW in the materials,which are accompanied by an abundance of heterogeneous interfaces to improve the dielectric loss.The Co_(2)NiO_(4)@MnCo_(2)O_(4.5)composites showed a minimum reflection loss(RLmin)of30.01 dB and a superior effective absorption bandwidth(EAB)of 6.12 GHz(11.88 GHze18 GHz)at a thickness of 2.00 mm.Computer Simulation Technology(CST)revealed that the obtained particles show very low radar crosssection(RCS)values and almost full coverage angles.The maximum reduction of RCS at vertical incidence reaches 19.98 dB m2.The Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles exhibit outstanding radar attenuation properties,which can effectively inhibit the reflection and scattering of EMW.Therefore,the prepared Co_(2)NiO_(4)@MnCo_(2)O_(4.5)absorbers have great application potential in the field of EMW absorption.展开更多
文摘Three sets of MXene(Ti_(3)C_(2)T_(x))@nano-Fe_(1)Co_(0.8)Ni_(1)composites with 15,45,and 90 mg MXene were prepared by in-situ liquid-phase deposition to effectively investigate the impact of the relationship between MXene(Ti_(3)C_(2)T_(x))and nano-Fe_(1)Co_(0.8)Ni_(1)magnetic particles on the electromagnetic absorption properties of the composites.The microstructure,static magnetic properties,and electromag-netic absorption performance of these composites were studied.Results indicate that the MXene@nano-Fe_(1)Co_(0.8)Ni_(1)composites were primarily composed of face-centered cubic crystal structure particles and MXene,with spherical Fe_(1)Co_(0.8)Ni_(1)particles uniformly distrib-uted on the surface of the multilayered MXene.The alloy particles had an average particle size of approximately 100 nm and exhibited good dispersion without noticeable particle aggregation.With the increase in MXene content,the specific saturation magnetic and coer-civity of the composite initially decreased and then increased,displaying typical soft magnetic properties.Compared with those of the Fe_(1)Co_(0.8)Ni_(1)magnetic alloy particles alone,MXene addition caused an increasing trend in the real and imaginary parts of the dielectric constant of the composite.Meanwhile,the real and imaginary parts of the magnetic permeability exhibit decreasing trend.With the in-crease in MXene addition,the material attenuation constant increased and the impedance matching decreased.The minimum reflection loss increased,and the maximum effective absorption bandwidth decreased.When the MXene addition was 90 mg,the composite exhib-ited a minimum reflection loss of-46.9 dB with a sample thickness of 1.1 mm and a maximum effective absorption bandwidth of 3.60 GHz with a sample thickness of 1.0 mm.The effective absorption bandwidth of the composites and their corresponding thicknesses showed a decreasing trend with the increase in MXene addition,reducing by 50%from 1.5 mm without MXene addition to 1 mm with 90 mg of MXene addition.
基金This work was supported by Natural Science Foundation of Shandong Province(ZR2022ME089)National Natural Science Foundation of China(52207249)Yantai Basic Research Project(2022JCYJ04).
文摘Cobalt nickel bimetallic oxides(NiCo_(2)O_(4))have received numerous attentions in terms of their controllable morphology,high temperature,corrosion resistance and strong electromagnetic wave(EMW)absorption capability.However,broadening the absorption bandwidth is still a huge challenge for NiCo_(2)O_(4)-based absorbers.Herein,the unique NiCo_(2)O_(4)@C core-shell microcubes with hollow structures were fabricated via a facile sacrificial template strategy.The concentration of oxygen vacancies and morphologies of the three-dimensional(3D)cubic hollow core-shell NiCo_(2)O_(4)@C framework were effectively optimized by adjusting the calcination temperature.The specially designed 3D framework structure facilitated the multiple reflections of incident electromagnetic waves and provided rich interfaces between multiple components,generating significant interfacial polarization losses.Dipole polarizations induced by oxygen vacancies could further enhance the attenuation ability for the incident EM waves.The optimized NiCo_(2)O_(4)@C hollow microcubes exhibit superior EMW absorption capability with minimum RL(RLmin)of-84.45 dB at 8.4 GHz for the thickness of 3.0 mm.Moreover,ultrabroad effective absorption bandwidth(EAB)as large as 12.48 GHz(5.52-18 GHz)is obtained.This work is believed to illuminate the path to synthesis of high-performance cobalt nickel bimetallic oxides for EMW absorbers with excellent EMW absorption capability,especially in broadening effective absorption bandwidth.
基金Project supported by the National Key R&D Program of China(Grant No.2021YFB3501302)the National Natural Science Foundation of China(Grant No.51731001)supported by the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization’s key of research and development projects。
文摘The easy-plane anisotropy of the Y_(2)Co_(17)rare earth soft magnetic alloy has high saturation magnetization and operating frequency,and good impedance matching.Therefore,it is expected to become a kind of high-performance microwave absorbing material.In this paper,Y_(2)Co_(17)alloy was prepared by a reduction-diffusion method,and its micropowder was prepared as polyurethane(PU)based composite absorbing materials(Y_(2)Co_(17)/PU composites).The microwave properties of composites with different volume fractions were calculated.The composites showed outstanding absorption characteristics in the range of 20-30 vol%,and the minimum reflection loss(RL)was less than-50 d B.When the volume fraction was25%,the effective absorption bandwidth could cover the X-band at a thickness of 1.5 mm,and the Ku-band at a thickness of1.08 mm.The absorption mechanism was analyzed by the interface reflection model.The RL absorption peak bandwidth mechanism was discussed by using the amplitude relation and calculating the effective absorption bandwidth at different thicknesses.The effective absorption bandwidth values were in good agreement with the theoretical expectation.
基金financial support from Ministry of Science and Technology of China(MoST,2016YFA0200200)the National Natural Science Foundation of China(NSFC,21875114,51373078,and 51422304)NSF of Tianjin City(15JCYBJC17700)。
文摘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.
基金financially supported by the National Natural Science Foundation of China (Nos.51407134 and 51801001)the Natural Science Foundation of Shandong Province (No.ZR2019YQ24)+6 种基金the China Postdoctoral Science Foundation (Nos.2016M590619 and 2016M601878)the Provincial Key Research and Development Program of Shaanxi (No.2019GY-197)the Qingchuang Talents Induction Program of Shandong Higher Education Institution (Research and Innovation Team of Structural Functional Polymer Composites)support from The Thousand Talents PlanThe World-Class University and DisciplineThe Taishan Scholar’s Advantageous and Distinctive Discipline Program of Shandong ProvinceThe World-Class Discipline Program of Shandong Province。
文摘To solve the electromagnetic pollution,herein,a CoFe_(2)O_(4)/C/PANI composite was developed by a green route,which was constructed with spinel of metal oxide,graphitized carbon and conductive polymer composites.Benefiting from the designable interfaces and increased dipoles,the microwave dielectric response capability can be boosted significantly and resulted in the enhanced microwave absorbing performance.As revealed by the reflection loss curve,the minimum reflection loss(RLmin) reached-51.81 dB at 12.4 GHz under a matched thickness of 2.57 mm.At 2.5 mm,the effective absorbing band covered 8.88 GHz,suggesting the desirable wideband feature.In our case,the method of utilization of a novel green way to fabricate multiple-component EM absorber can be a promising candidate for high-performance EM absorber.
基金Project supported by the National Key Research and Development Program of China (2017YFB0304301)the National Natural Science Foundation of China (51804346)China Postdoctoral Science Foundation(2020T130730)。
文摘Traditional ferrites are of poor electromagnetic wave(EMW) absorption while doping rare earth elements(REEs) can greatly enhance their permeability to improve the EMW loss performance.In this study,Co-Zn ferrite nanoparticles doped with various amounts of REEs(Gd^(3+),Nd^(3+)and Pr^(3+)) were synthesized by a hydrothermal method,and their particle morphology and an EMW absorption performance were characterized by using transmission electron microscopy(TEM) and a Vector network analyzer(VNA).The results show that the initial spherical Co-Zn ferrite nanoparticles present an irregular quadrilateral structure after Gd^(3+)doping,and the average particle size of Co_(0.5)Zn_(0.5-x)Gd_(x)Fe_(2) O_(4) increases from 26 to 50 nm with x increasing from 0 to 0.35.At x of 0.25,the reflectivity absorbance achieves-27.94 dB at 18 GHz with the effective absorption bandwidth(EAB) of 4.08 GHz at a sample thickness of 2.5 mm.When Nd^(3+)doping amount reaches x=0.3,the minimum reflection loss(RL)is-25.63 dB at 18 GHz and EAB is 3.91 GHz.Doping Pr^(3+)(x=0.25) in the sample broadens EAB,and the minimum RL is-16.1 dB at 16.81 GHz and EAB is 7.31 GHz.This study shows that the magnetic moment produced by doping REES can form magnetic domains,which affects the incident EMW and improves the magnetic loss.It is expected that REEs-doped Co-Zn ferrite nanoparticles can be used as efficient electromagnetic shielding materials in aerospace.
基金supported by the National Natural Science Foundation of China(No.52373271)the Open Foundation of the Key Laboratory of Multispectral Absorbing Materials and Structures,Ministry of Education(No.KPKFJJ20250011-2).
文摘Hollow engineering is considered to be an essential subfield in promoting electromagnetic(EM)wave absorption intensity and realizing lightweight characteristics.However,the enhancement of the effective absorption bandwidth(EAB)still faces considerable challenges.Herein,hollow carbon nanocages with CoFe_(2)Se_(4)quantum dots(HCNs@CoFe_(2)Se_(4)-QDs)with superior EM wave absorption intensity and ultra broadband EAB are produced by using tightly arranged SiO_(2)spheres as hard-template materials.Specifically,the removal of SiO_(2)templates inevitably results in the formation of a hollow cavity,which is favorable for optimizing impedance matching and increasing the absorption intensity.In addition,the incorporation of selenium powder effectively increases the number of heterogeneous interfaces by forming CoFe_(2)Se_(4)quantum dots(QDs)during the pyrolysis process,leading to strengthened interfacial polarization and ultra broadband EAB.As a result,superior EM wave attenuation with a minimum reflection loss(RL)of−67.6 dB and an EAB of 11.4 GHz is achieved with only a 20 wt%filler ratio.This design concept of hollow engineering with magnetic QDs provides inspiration for optimizing the EM wave absorption intensity and simultaneously promoting the absorption bandwidth.
基金the National Natural Science Foundation of China under Grant Nos.51972089,51672064,U1435206.
文摘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,(Ce0.2Hu0.2Sm0.2Er0.2Yb0.2)B6,(Ce0.2Y0.2Eu0.2Er0.2Yb0.2)B6,(Ce0.2Ya2Sm0.2Eu0.2Yb0.2)B6,and(Nd0.2Y0.2Sm0.2Eu0.2Yb0.2)B6 possess CsCl-type cubic crystal structure,and their theoretical densities range from 4.84 to 5.25 g/cm^(3).(Ce02Y0.2Sm0.2Er0.2Yb02)B6 powders with the average particle size of 1.86 jim 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 REB03(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/HEREB03 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.
基金We are thankful to the financial support from the National Natural Science Foundation of China(grant No.51971111)Innovation Project of Nanjing University of Aeronautics and Astronautics(grant No.xcxjh20210604)。
文摘Nanocomposites with heterogeneous structures and magneto-electric synergistic losses have broad prospects for improving electromagnetic wave(EMW)absorption performance.In this study,we synthesized Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles with abundant hetero-interfaces and multiple magnetoelectric loss mechanisms by a facile hydrothermal method.The excess 0.5 oxygen atoms in MnCo_(2)O_(4.5) produce more vacancies and contribute to the enhancement of electrical conductivity.Sequential nanoneedle clusters facilitate multiple reflections and absorption of EMW in the materials,which are accompanied by an abundance of heterogeneous interfaces to improve the dielectric loss.The Co_(2)NiO_(4)@MnCo_(2)O_(4.5)composites showed a minimum reflection loss(RLmin)of30.01 dB and a superior effective absorption bandwidth(EAB)of 6.12 GHz(11.88 GHze18 GHz)at a thickness of 2.00 mm.Computer Simulation Technology(CST)revealed that the obtained particles show very low radar crosssection(RCS)values and almost full coverage angles.The maximum reduction of RCS at vertical incidence reaches 19.98 dB m2.The Co_(2)NiO_(4)@MnCo_(2)O_(4.5)nanoparticles exhibit outstanding radar attenuation properties,which can effectively inhibit the reflection and scattering of EMW.Therefore,the prepared Co_(2)NiO_(4)@MnCo_(2)O_(4.5)absorbers have great application potential in the field of EMW absorption.
