Electromagnetic wave absorption properties of polymer-derived magnetic carbon-rich SiCN-based composite ceramics

In this paper, the mixture of Fe and Ni nanoparticles (abbreviated as FeNi) was added to liquid polysilazane (PSZ) as a magnetic source, to prepare a series of magnetic carbon-rich SiCN-based composite ceramics by adjusting the mass ratio of FeNi through the polymer derivation method. The phase composition, microstructure, conductivity, electromagnetic wave (EMW) absorption performance and mechanism of composite ceramics prepared were discussed. The analysis shows that the introduction of magnetism has adjusted the impedance matching and improved the magnetic loss performance of composite ceramics on the whole, and the dielectric loss ability of composite ceramics has been strengthened benefiting from the formation of conductive path of CNTs precipitated by FeNi catalysis in the matrix. Therefore, the addition of magnetic particles improves the EMW absorption peak intensity and effective absorption bandwidth (EAB) of composite ceramics. When the addition amount of FeNi was 5 wt%, the sample 5# exhibited the best comprehensive EMW absorption performance: Its minimum reflection loss (RL_min) was ?18 dB and the EAB was 2.5 GHz when the thickness was 1 mm, the EAB covering the C, X and Ku bands can be obtained by adjusting the thickness from 1.0 mm to 4.0 mm. Through calculation, the EAB (EAB_tf) of 5# with a thickness of 1 mm and a filling rate of 1 wt% can reach 50, which is significantly higher than that of a series of SiCN-based composite ceramics previously reported. In addition, the density of 5# was 2.3 g/cm³, and its compressive strength (CS) can reach 337 MPa. The data shows that the composite ceramic 5# prepared in this experiment has the merits of light weight, excellent comprehensive EMW absorption performance and good compression resistance, and is expected to be one of the promising materials in the field of new-generation EMW absorbers.     

Microstructure and EMW absorption properties of CVI Si3N4–SiCN ceramics with BN interface annealed in N2 atmosphere

A kind of chemical vapor infiltration (CVI) Si₃N₄–BN–SiCN composite ceramic with excellent electromagnetic wave (EMW) absorbing properties is obtained by CVI BN interface and SiCN matrix on porous Si₃N₄ ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N₂ atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI SiCN ceramics with BN interface were crystallized in the form of nanograins, and the crystallization temperature was lower. Moreover, both EMW absorbing properties and mechanical properties of CVI Si₃N₄–BN–SiCN composite ceramics firstly increased and then decreased with the increase in annealing temperature due to the influence of BN interface on the microstructure and phase composition of the composite ceramics. The minimum reflection coefficient (RC) and maximum effective absorption bandwidth (EAB) of the composite ceramics annealed at 1300°C were ?47.05 dB at the thickness of 4.05 mm and 3.70 GHz at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MPa and 1.78 MPa/m^1/2, respectively.     

Effect of boron content on the microstructure and electromagnetic properties of SiBCN ceramics

Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was ?35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached ?29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties.     

Microstructure and electromagnetic wave absorption property of reduced graphene oxide-SiCnw/SiBCN composite ceramics

In this account, RGO-SiC_nw/SiBCN composite ceramics were fabricated using polymer derived ceramic (PDC) combined with chemical vapor infiltration (CVI) technology. Dielectric property of as-obtained RGO-SiC_nw/SiBCN composite ceramics was significantly enhanced thanks to established conductive pathway through overlapped nanoscale SiC_nw and micro-sized RGO. The minimum RC of composite ceramics with 0.5 wt% GO and 2.29 wt% SiC_nw at thickness of 3.6 mm reached -42.02 dB with corresponding effective absorption bandwidth (EAB) of 4.2 GHz. As temperature rose from 25 to 400 °C, permittivity increased with enhanced charge carrier density and then it decreased due to oxidation process of RGO from 400 to 600 °C. The minimum reflection coefficient (RC) was recorded as -39.13 dB and EAB covered the entire X-band at 600 °C. EMW absorption ability was evaluated after high-temperature oxidation experiment under protective effect of wave-transparent Si₃N₄ coating. RGO-SiC_nw/SiBCN composite ceramics maintained outstanding EMW absorption ability with minimum RC of -10.41 dB after oxidation at 900 °C, indicating RGO-SiC_nw/SiBCN composite ceramics with excellent EMW absorption characteristic even at high temperatures and harsh environments.     

Si3N4-BN-SiCN ceramics with unique hetero-interfaces for enhancing microwave absorption properties

SiCN-based ceramics with broadband and strong microwave absorption properties are desired for the structural and functional integration of ceramic matrix composites. The elemental composition and thermal expansion coefficients of the ceramics matrix crucially affect its microstructure and electromagnetic wave (EMW) absorption properties. BN layer with lower electrical conductivity and higher specific area, exhibits both the impedance matching characteristic and EMW attenuation in the process of multiple reflections, electrical conductivity loss, dipole polarization and interfacial polarization. Therefore, Si₃N₄-BN-SiCN ceramics, which were synthesized using chemical vapor infiltration (CVI) method, construct unique hetero-interface of Si₃N₄-BN, Si₃N₄–SiCN and BN-SiCN. Therefore, the Si₃N₄-BN-SiCN ceramics have outstanding EMW absorption performance and realize an effective absorption bandwidth (EAB) that covers the whole X band and the minimum reflection coefficient (RC) reaches -18.43 dB at a thickness of 3.37 mm.     

Highly dense 0.3CaCeNbWO8-0.7LaMnO3 composite ceramics fabricated by cold sintering process

The cold sintering process (CSP) has been used for fabricating functional ceramics at a low sintering temperature. In this study, highly dense 0.3CaCeNbWO₈-0.7LaMnO₃ composite ceramics have been successfully fabricated by CSP. The phase structure, microstructure, and electrical properties of composite ceramics have been investigated. The composite ceramic is mainly composed of a tetragonal CaCeNbWO₈ phase with scheelite structure and an orthorhombic LaMnO₃ phase with perovskite structure. The relative density of composite ceramic is 94.5%, and is higher than that of single phase ceramic. The resistivity of composite ceramic exhibits negative temperature coefficient characteristics, with an aging coefficient less than 2%. Such a sintering methodology is of great significance, since it provides a feasible idea for preparing composite ceramics.     

Ultra-broadband electromagnetic wave absorption of ceramic composite coating by atmospheric plasma spraying

Dy doped ceramic material of Ba₄Fe_2.6Dy_1.4Nb₈O₃₀ with the tetragonal black bronze structure was synthesized by solid-state reaction at 1300°C. The composite powders of Ba₄Fe_2.6Dy_1.4Nb₈O₃₀/FeSiAl with good flowing were prepared by spray drying using the powders slurry. The obtained composite powders were then plasma sprayed to fabricate coating. The microstructure and absorption characteristics of electromagnetic wave (EMW) of the coating materials are investigated. Results show that the composite powders significantly remain the phase stability during atmospheric plasma spraying and adsorbing heredity of EMW for the coating. The coating powders have excellent EMW absorption with the minimum reflection loss of −48.20 dB at the thickness of 3.5 mm. Also, the coating powders display the maximum effective absorption bandwidth of 6.24 GHz at the thickness of 1.5 mm, which covers the X-band. Moreover, the coating was found to have a certain EMW absorption performance at high temperature of 700°C. The Ba₄Fe_2.6Dy_1.4Nb₈O₃₀ ceramic material with low thermal conductivity ensured the electromagnetic absorption capacity of the coating at high temperature. The Ba₄Fe_2.6Dy_1.4Nb₈O₃₀/FeSiAl ceramic composite materials could have the potential applications as the high temperature EMW absorber.     

Effect of SiBCN content on the dielectric and EMW absorbing properties of SiBCN-Si3N4 composite ceramics

Siliconboron carbonitride ceramics (SiBCN) were introduced into porous Si₃N₄ substrates via low pressure chemical vapor deposition and infiltration from SiCl₃CH₃-NH₃-BCl₃-H₂-Ar system. To improve the electromagnetic wave(EMW) absorbing properties, the molar ratio, n_CH3SiCl3/(n_NH3 + n_BCl3), was increased based on thermodynamics analysis. The results show that nanosized silicon carbide crystals and free carbon dispersed uniformly in the amorphous SiBCN phase, resulting in suitable dielectric properties and improved absorption capabilities of SiBCN-Si₃N₄ ceramics. Additionally, with increasing SiBCN ceramics loading, the amount of nanocrystals and interface between nanocrystals and amorphous SiBCN phase increased, leading to enhanced polarization and dielectric loss of the composite ceramics. When SiBCN content was up to 3.64 wt%, the electromagnetic reflection coefficient (RC) of SiBCN-Si₃N₄ composite ceramics reached ?40 dB (>99.97% absorbing) with the effective electromagnetic absorbing bandwidth of 3.64 GHz in the X-band. This study makes it possible to fabricate SiBCN-based composite materials with excellent EMW absorbing properties at a low temperature.     

High recoverable energy storage density in nominal (0.67-x)BiFeO3-0.33BaTiO3-xBaBi2Nb2O9 lead-free composite ceramics

A series of novel lead-free energy storage ceramics, (0.67-x)BiFeO₃-0.33BaTiO₃-xBaBi₂Nb₂O₉ (BF-BT-xBBN), were fabricated by traditional solid-state reaction, where bismuth layer-structured BaBiNb₂O₉ was incorporated into perovskite-structured BiFeO₃–BaTiO₃ ceramic as an additive. The addition of BaBi₂Nb₂O₉ increased the relaxor behavior and breakdown strength of BF-BT ceramics due to the formation of polar nanoregionals (PNRs), inducing enhanced energy storage performance. The composite ceramics, with x = 0.08, showed a large recoverable energy density (W_rec) of 3.08 J/cm³ and an outstanding energy storage efficiency (η) of 85.57% under an applied electric field of 230 kV/cm. Moreover, the composite ceramics exhibited excellent thermal stability and high stability toward different frequencies in a temperature range of 20–100 °C and a frequency range of 0.1–1500 Hz. These results demonstrate great potential of novel BF-BT-xBBN composite ceramics for next-generation energy storage applications.     

Polymer-derived Co2Si(Co)/SiCN composite ceramics with tunable microwave absorption properties

In this paper, Co₂Si(Co)/SiCN composite ceramics were synthesized by simple precursor-derived ceramics method. The phase composition, morphology, and microwave absorption properties of Co₂Si(Co)/SiCN composite ceramics at different pyrolysis temperatures (1000–1400°C) were studied. When pyrolysis temperature was 1300°C, carbon nanowires (CNWs), Co₂Si, Si₂N₂O, SiC and Si₃N₄ were in situ generated and the best electromagnetic wave (EMW) absorption performance was obtained. The minimum reflection loss reached−50.04 dB at 4.81 mm, and the effective absorption bandwidth broadened to 3.48 GHz (14.52–18 GHz) at 1.31 mm. The excellent EMW absorption performance mainly comes from the coexistence of multiple loss mechanisms, including the magnetic loss of Co₂Si, the conduction loss of CNWs, and the heterogeneous interfaces polarization between varieties of nanocrystals and amorphous ceramic matrix. By adjusting the sample thickness from 1 to 5 mm, the effective absorption of S1300 can cover the entire X and Ku bands, from 3.36 to 18 GHz. This study provides a simple way to synthesize high performance ceramic-based microwave absorbing materials.     

The heterointerface of graphene in-situ growth for enhanced microwave attenuation properties in La-doped SiBCN ceramics

The electromagnetic wave (EMW) absorbing materials are widely applied to attenuate the useless and harmful EMW generated from wireless communication and 5G networks, which could protect the human health and electronic device safety. In this study, La-doped SiBCN ceramics with broadband EMW absorption capability were prepared via generating abundance of heterointerfaces, as graphene were in-situ grown by La₂O₃ catalyzing. The graphene in-situ formed in the ceramics can be attributed to the La atom decreasing the potential energy of the free carbon ring nucleation from −760.9 Ha to −8984.3 Ha. Consequently, the electrical conductivity of the SiBCN ceramics improved from 12.360 S/m to 18.025 S/m, the minimum reflection loss (RL_min) obtained was −26.48 dB at 7.2 GHz and the effective absorption bandwidth (EAB) was 6.32 GHz (11.68–18.00 GHz) at a thickness of 1.7 mm. At 700 °C, the RL_min and EAB values reached −43.18 dB and 4.2 GHz, respectively. The enhanced EMW absorbing capability can be attributed to the rationally tailor the heterointerfaces to improve the polarization loss and conduction loss of the SiBCN ceramics. The interfaces between graphene and amorphous phases generate built-in electric fields and space chare regions to strengthen the interface polarization, while the electrons migrating rapidly in the graphene and other crystals improved the electrical conductivity. The positive effect of heterointerfaces regulation of graphene in-situ growth improved the dielectric loss capacity of the SiBCN ceramics; therefore, this study provides a feasible method to enhance the EMW absorption capability of polymer-derived ceramics.     

Enhanced electromagnetic wave absorbing properties of Si-O-C ceramics with in-situ formed 1D nanostructures

The Si-O-C ceramics were prepared by polymer-derived ceramic method using polysiloxane/FeCl₃ as precursor with the FeCl₃ content of 1.0 wt%. The microstructure, dielectric properties, and electromagnetic wave (EMW) absorbing properties in X band of the Si-O-C ceramic were investigated. It was found that the pyrolysis temperature has a great influence on the amount of in-situ formed CNTs and the transformation from CNTs to 1D SiC nanostructures. With the temperature rising from 1000 to 1500°C, the SiC formed with various morphologies including SiC microspheres, needle-like SiC, and SiC nanowires which were transformed from CNTs. The EMW absorbing properties were dramatically improved when the pyrolysis temperature raised to 1500°C; the minimum reflection loss (RL) was −58.37 dB of sample with a thickness of 2.95 mm at 10.11 GHz, and the absorbing band (RL ≤−20 dB) of sample at a thickness of 3.0 mm covers 3.8 GHz (8.2-12.0 GHz), which means more than 99% of the EMW were absorbed. The enhancement of EMW absorbing properties of bulk Si-O-C ceramics was attributed to the interfacial polarization induced by in-situ heterogeneous nanostructures with complex interfaces.     

Orange-emitting MgO–(Sr,Ba)3SiO5:Eu composite phosphor ceramics for turn signals and warm white laser lighting

The research and development of orange-emitting phosphor ceramics with excellent performance are significant for improving the optical quality of laser lighting and developing-related emerging applications. For the first time, we prepared an orange-emitting MgO–(Sr,Ba)₃SiO₅:Eu composite phosphor ceramic with high thermal conductivity, high thermal stability, and excellent luminescence properties. The thermal conductivity of the phosphor ceramic is as high as 32 W/(m K), and the luminescence intensity decreases by only 20% at 200°C, both of which are better than other orange-emitting phosphor ceramics reported so far. The luminous efficacy of the phosphor ceramic (41.6 lm/W) is also close to the highest value of orange-emitting phosphor ceramics until now. In addition, we also explored the application prospects of the composite phosphor ceramics in automotive turn signals and warm white laser lighting. This work provides inspiration for the preparation of other excellent orange-emitting phosphor ceramics in the future.     

Modeling and Monte Carlo simulation on photothermal effect in Gd3Al3Ga2O12:Ce3+/Y3Al5O12:Cr3+ layered composite ceramic

Layered composite ceramics have wide application in solid-state lasers. However, the photothermal effect in the layered ceramics has not been clarified, due to the interface effect between layers. In this work, the model of photon propagation and thermal distribution in the Gd₃Al₃Ga₂O₁₂:Ce³⁺/Y₃Al₅O₁₂:Cr³⁺ layered ceramics are established. The property of photon absorption, reflection, transmission, and thermal distribution are studied by combining the Monte Carlo method and the convolution method. It is found that the photon absorption distribution and thermal distribution of this layered ceramics show the gradient change. Furthermore, this change is strongly dependent on the type, beam width, and power of laser. The temperature of layered ceramics induced by Gaussian beam is higher than that induced by flat circular beam. This work provides a useful research method for the design of layered ceramic materials with excellent scintillation performance.     

Enhanced electromagnetic microwave absorption properties of SiCN(Fe) ceramics produced by additive manufacturing via in-situ reaction of ferrocene

SiCN(Fe) ceramics with excellent electromagnetic wave (EMW) absorption performance were successfully prepared from a preceramic polymer doped with ferrocene. Additive manufacturing (Digital Light Processing), providing enhanced structural design ability, was employed to fabricate samples with complex architectures. During pyrolysis, ferrocene catalyzed the in-situ formation of a large amount of turbostratic carbon, graphite and SiC nanosized phases, which formed carrier channels in the electromagnetic field and increased the conductivity loss. Meanwhile, it also increased the dipole polarization, interface polarization and the dielectric properties of the material, which finally enhanced the EMW absorption capacity of SiCN(Fe) ceramics. When containing 0.5 wt% ferrocene, the material showed good performance with EAB 4.57 GHz at 1.30 mm, and RL_min −61.34 dB at 2.22 mm. The RL_min of 3D-SiCN-0.5 ceramics was −6 dB, and the RL of the X-band was lower than −4 dB at 2 mm.     

Morphology-controlled preparation and tunable electromagnetic wave absorption performance of manganese dioxide nanostructures

The development of electromagnetic wave (EMW) absorption materials with lightweight, wide absorption bandwidth, thin thickness, and strong EMW absorption performance has become a hotspot. Herein, the morphology-controlled preparation of α-manganese dioxide (α-MnO₂) was successfully obtained via a facile hydrothermal method, and the EMW absorption performance of α-MnO₂ was investigated in detail. The results indicated the as-obtained Mn-1.0-120 possessed the best EMW absorption performance with minimum reflection loss of −53.43 dB at about 5.2 GHz with a thickness of 4.1 mm originated from the synergistic effects of multiply scattering, dielectric loss, and magnetic loss. This contribution demonstrates that the MnO₂ has promising candidates with a tunable EMW absorption performance for applications in the electromagnetic field in the future.     

3D printed crack-free SiOC(Fe) structures with pyrolysis-induced carbon nanowires for enhanced wave absorption performance

High-performance SiOC(Fe) wave-absorbing ceramics, containing a large number of carbon nanowires, were successfully prepared using a combination of photopolymerization 3D printing technology and the polymer-derived ceramic pyrolysis method. By employing an optimized segmented slow heating scheme with extended holding time, the pyrolysis of SiOC(Fe) ceramics at 1000 °C facilitated the growth of carbon nanowires, Fe₃C and SiO₂ grains. These carbon nanowires were interlaced and interconnected within the samples, forming abundant conductive networks. This highly conducive network efficiently converted electromagnetic energy into thermal energy, effectively dissipating electromagnetic waves, and consequently enhancing the microwave absorption performance of ceramics. Moreover, this approach not only reduced ceramic cracks but also improved the dielectric loss performance of the materials, achieving a minimum reflectivity value of −35.72 dB. The SiOC(Fe) ceramics added with 5 wt% VcFe effectively enhanced the magnetic loss of the material, reduced the difference between the relative complex permeability (μ_r) and the relative complex dielectric constant (ε_r), and improved the impedance matching between the material surface and air, thereby further improving its microwave absorption performance. This resulted in an increase in the maximum effective absorption bandwidth of the material to 12.7 GHz at 5 mm. This study offers a promising solution for the preparation of ceramic matrix composite materials incorporating carbon nanowires, magnetic particles and ceramic precursors, which would be potentially valuable for radar detection and sensor applications.     

Dielectric,ferroelectric and magnetoelectric properties of in-situ synthesized CoFe2O4/BaTiO3 composite ceramics

Magnetoelectric composite materials have attracted more and more attention because of their coupling of ferroelectricity and ferromagnetism. It is a hotspot to realize the combination of ferromagnetic phase and ferroelectric phase. In this work, we used a new strategy to prepare CoFe₂O₄/BaTiO₃ composite ceramics: firstly, porous ferromagnetic CoFe₂O₄ phase was prepared by annealing of MOFs (metal organic frameworks) precursor Fe₃[Co(CN)₆]₂. And then, the ferroelectric BaTiO₃ phase in-situ grew in the pores of CoFe₂O₄ by a hydrothermal method. In the end, the CoFe₂O₄/BaTiO₃ composite ceramics sintered at different temperatures have been synthesized. The effects of sintering temperature on the structure, dielectric and ferroelectric properties have also been studied. Because the crystallinity and density increase with the increase of sintering temperature, the composite ceramic sintered at 1200 °C shows the best dielectric properties. It is found that sintering temperature has little effect on the ferroelectric and magnetic properties of ceramics. Taking the CoFe₂O₄/BaTiO₃ composite ceramic sintered at 1200 °C as an example, derived from the interaction between the ferromagnetic CoFe₂O₄ phase and ferroelectric BaTiO₃ phase, the applied magnetic field lead to the reduction of P_r and E_c.     

Structure,electrical and luminescent properties of the NBT:Er-0.3CT:Pr composite ceramics

A binary composite ceramic Na_0.5Bi_0.5TiO₃:0.002 Er-0.3CaTiO₃:0.003 Pr (NBT:Er-0.3CT:Pr) was fabricated by a conventional solid state reaction route. The effect of sintering temperature on the microstructure and phase structure of the ceramics has been investigated. And the basic electrical properties such as dielectric properties and ferroelectric performances of the ceramics were examined. Macro long-ranged ferroelectric order cannot be induced via electric field in the composite ceramics. And under local electric field using PFM, obvious ferroelectric switching is identified in the ceramics. Furthermore, the up-conversion luminescence, photochromic reaction, and luminescence modulation have been achieved in the ceramics. Additionally, photo-stimulated luminescence and thermal luminescence are obtained. The present study indicates that optical properties are tightly related to the sintering temperature. The prepared ceramic NBT:Er-0.3CT:Pr owns a piezoelectric performance and multi luminescence properties, which can widen the applications of ferroelectric ceramics.     

Synchronous improvement of piezoelectric property and temperature stability in PSN-PMN-PT ceramics by forming composites with ZnO

Relaxor ferroelectric materials with high piezoelectric properties always suffer from low phase transition temperature, making them difficult to satisfy the demands for high-temperature environment applications. In this work, we proposed a composite approach to improve the piezoelectricity and temperature stability of PSN-PMN-PT ceramics at the same time. The ZnO nanoparticles as a second phase were introduced into the PSN-PMN-PT matrix to form composite ceramics. When the ZnO content reaches 5 mol%, the piezoelectric constant d₃₃ increases from 529 pC/N for pure PSN-PMN-PT ceramic to 590 pC/N. Meanwhile, the retained d₃₃ after annealing at 200 °C keeps 92% of the value before annealing, indicating the thermal depolarization behavior is suppressed by the composite method. The synchronous improvement of the d₃₃ and thermal depolarization behavior for PSN-PMN-PT/ZnO composite ceramics is related to the local electric field and stress field caused by the addition of ZnO particles. Our results pave a simple and effective way to develop next-generation PT-based relaxor ferroelectric ceramics.