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The (La1/2Ta1/2)xTi1-xO2 and (Er1/2Ta1/2)xTi1-xO2 ceramics with x = 0.01 and 0.03 were synthesized by a conventional solid-state reaction. The analysis of EDS mapping, ac conductivity spectra, impedance analysis, XPS, and DC bias indicate that electrons-pinned defect-dipole (EPPD) polarization plays the main role in both the (La1/2Ta1/2)0.01Ti0.99O2 and (Er1/2Ta1/2)0.01Ti0.99O2 ceramics, while the interfacial polarization and hopping polarization are respectively highlighted by the (La1/2Ta1/2)0.03Ti0.97O2 and (Er1/2Ta1/2)0.03Ti0.97O2 ceramics. Besides, the dielectric responses reveals that the interfacial polarization and hopping polarization are much slower than EPDD polarization and lead to poor frequency-, temperature-stability and higher dielectric loss (tanδ). Then the conclusion can be drawn that the outstanding dielectric properties can be achieved only the EPDD polarization takes the absolute dominant position, and excellent properties are obtained in (Er1/2Ta1/2) 0.01Ti0.99O2 ceramic with ultra-low loss of tanδ≈0.0095 (@1 kHz) and excellent frequency, temperature and DC bias stability.

Carbon nanofibers embedded with magnetic Fe3C nanoparticles have been synthesized using electrospinning technique, followed by one-step carbonization. By using Fe3C/C nanofibers as filler with 10% content, the sample can achieve a minimum reflection loss (RL) of −54.94 dB with a thickness of 1.36 mm, as well as the broad effective absorption bandwidth (EAB) can reach to 4.5 GHz (13.3–17.8 GHz) at the thickness of 1.55 mm. The superior properties might be due to the synergistic effects of dielectric loss, magnetic loss, multiple scattering and reflection. This work presents a facile and promising method to produce high performance microwave absorption materials with thin thickness, light weight and strong absorption.

A novel core-shell BaFe12O19@C composite with glucose-based carbon was successfully synthesized by the hydrothermal carbonization and subsequent calcinations. The phase structure, morphology and the microwave absorption properties of all the as-prepared samples were characterized by XRD, SEM and vector network analyzer, respectively. The results show that dielectric loss of BaFe12O19@C composites can be enhanced due to the introduction of carbon, which causes improved matching impedance and microwave absorption properties of BaFe12O19@C composites. The optimal maximum reflection loss is −73.42 dB with a thickness of 1.40 mm in the frequency range of 2–18 GHz. We believe that the BaFe12O19@C composites are promising candidates as highly effective microwave absorbers. Furthermore, the biomass carbon is expected to have further applications in the field of microwave absorption.

Carbon fibers exhibit the potential as lightweight absorbers, however, their high conductive capability often results in much reflection waves on the absorber surfaces. Here, novel ZnO/carbon porous nanofibers were derived from zinc-based organic-metal frameworks (MOFs, ZIF-8) by electro-spinning method. The porous structures make a great contribution to dielectric loss. In addition, the conductive networks can also provide more pathways for electrons transferring. With the good impedance matching and attenuation capability, ZnO/carbon porous nanofibers display good microwave response ability. The minimum reflection loss (RL) is −22.89 dB at 16.2 GHz with 1.5 mm, the effective absorption bandwidth (fE) reach 5.64 GHz. In this work, the influences of microstructure on electromagnetic parameters and absorbing properties are revealed by designing the novel porous carbon fibers.

In this study, a facile metal-organic framework (MOF) derived strategy was rationally designed in situ carbon nanotubes encapsulated metal nickel from Ni–Zn- MOFs. Hierarchical ZnO–Ni@C materials consist of nanorods-composed shell and a microsphere yolk. Most of the nickel metal wrapped by the graphitized carbon layers or encapsulated at the top of the carbon nanotubes. Meanwhile, the ZnO nanoparticles randomly distribute in this yolk-shell structure. It is worth mentioning that the pyrolysis temperature plays a crucial factor in the formation process of porous ZnO–Ni@C composites with semiconductor, magnetic metal nanoparticles and carbon matrix. In order to explore the microwave absorption properties, associated chemical properties, morphology and electromagnetic parameters of the ZnO–Ni@C materials are discussed in detail. With the high surface area, special yolk-shell structure, outstanding electron transportability and the combined magnetic and dielectric loss, the optimized ZnO–Ni@CNT exhibits excellent polarization loss ability, strong microwave energy dissipation, and wide absorption band. The optimal microwave absorption property in ZnO–Ni@CNT reaches a minimum reflection loss (RL) value of −58.6 dB at 2.3 mm, and effective absorption frequency range (RL ≤ −10 dB) of 4.8 GHz. Those results show that the polarization relaxation, the conductive network, multiple reflection, and special interface structure favor to the microwave absorption performance.

Li2Mg2.88Ca0.12TiO6 (LMCT) was modified by silane coupling agent (C14H19F13O3Si, F8261), and then filled in polytetrafluoroethylene suspension (PTFE) using hot treating approach. The weight fraction of LMCT varied from 30 to 70 wt %. XRD patterns presented the crystal phase of LMCT powders. The analyses of TEM, XPS, and FTIR were performed to characterize the surface states of LMCT fillers. The effects of LMCT filling content on the microstructure and dielectric properties were also investigated. Several theoretical models were discussed and compared with the dielectric constant of LMCT/PTFE substrates with respect to different LMCT content. Furthermore, the temperature and frequency dependence of dielectric constant were also considered on the composites. At last, the LMCT/PTFE composite substrates possessed relatively high dielectric constant (er = 4.33) and extremely low dielectric loss (tan δ = 0.001) at filler loading of 50 wt % LMCT.

High temperature ferroelectricity (T c ∼435 °C, E c ∼6.15 kV/cm & P r ∼0.16 μC/cm 2 ) was observed in a novel 3D hierarchical dysprosium (Dy)-doped ZnO nanorods-nanosheets (NRs-NSs) architecture synthesized using wet chemical co-precipitation method. Such a conclusion was drawn on the experimental confirmation obtained from the temperature variation of real part of dielectric constant and the room temperature P–E hysteresis loop. Dy 3+ doping strongly modified the morphology of ZnO from nanotaper to hierarchical NRs-NSs architecture. Lattice strain ( e ), crystallite size (L), deformation stress (σ), and deformation energy density (u) of both pristine nanotapers and 3D hierarchical Dy-ZnO NRs-NSs architectures were evaluated using line broadening analysis followed by the Debye-Scherrer and Williamson-Hall methods. Temperature variation of real component of dielectric constant ( e ′) for Dy-doped ZnO NRs-NSs architecture attains a maxima ( e ′ m ∼34,500) at ferro-to para-electric transition temperature, T c ∼435 °C. Temperature dependent complex component of dielectric constant ( e ''), tangent dielectric loss (tan δ) and ac conductivity (σ) were found to increase with rise in temperature. The frequency dependent dispersion plots of dielectric properties of Dy-ZnO NPs showed a decrease in dielectric constant and tangent loss with increase in frequency whereas ac conductivity showed an opposite trend. The Dy-doped ZnO NRs-NSs architectures exhibit feeble ferroelectricity with a remnant polarization (P r ) of 0.16 μC/cm 2 and a coercive field (E c ) of 6.15 kV/cm at room temperature. Moreover, the novel Dy-doped nanorods-nanosheets architectures with high temperature ferroelectricity will pave the pathway towards designing futuristic material in the field of low-power and wide-temperature ferroelectric based memory devices.

SiC/Fe2O3/Fe3O4/Fe embellished graphite layers (SiC/FexOy EGL) have attracted the interest of many scholars due to their excellent absorbing properties. Here, for the first time, a method for obtaining the SiC/FexOy EGL with silica sol, FeCl3, and graphite layers (GL) as raw materials by facile co-precipitation and then heat treatment at different temperatures is reported. For the SiC/FexOy EGL, the dielectric constant can be adjusted by controlling the heat treatment temperature. The prepared SiC/FexOy EGL architecture exhibits characteristics of broad bandwidth, excellent high frequency absorbing properties, and adjustable dielectric properties which attribute to the combination losses, such as the magnetic loss of FexOy, the dielectric loss of SiC and GL. The minimum reflection loss (RL) can reach −41.8 dB at 14 GHz in absorbent/paraffin composites. The bandwidth of the RL below −10 dB covers 6.56 GHz (11.28–17.84 GHz) with a thickness of 2 mm. The microwave absorption mechanism of the SiC/FexOy EGL composites is studied and the microwave absorption of the composites is improved.

Zirconium doped cobalt ferrite nanoparticles (Co1-xZrxFe2O4 where x = 0, 0.25, 0.50, 0.75 and 1) have been successfully engineered via co-precipitation method. X-ray diffraction studies reveal single phase cubic spinel structures up to Zr content of 50% with average sizes in the range of 16–26 nm.Particle sizes decrease with Zr doping due to increased strain in the crystal lattice. Fourier Transform Infrared and Raman spectra reveal the formation of mixed spinel ferrite particles. Presence of cobalt, zirconium, iron and oxygen in the prepared nanoparticles were identified by X-ray fluorescence analysis. Morphology of the samples investigated by Transmission Electron Microscopy shows the formation of nearly spherical particles. The surface characteristics identified by X-ray photoelectron spectroscopy confirms the substitution of zirconium ions mainly into octahedral sites with partially inversespinel structure. Thermal stability studies proves that ferrite formation to be a continuous process. Electrical properties such as dc resistivity as a function of temperature and ac conductivity with frequency were studied for all samples. The variation of dielectric properties like dielectric constant and dielectric loss are also studied as a function of frequency and these results reveal that the dispersion is due to interfacial polarization and hopping of charge carriers. Saturation magnetization, remanence and coercivity values changes with Zr substitution. The high coercive field obtained for Zr doped samples reveals their ferromagnetic nature suggesting a wide range of applications in telecommunication, data processing, consumer electronics, aerospace, catalysis and bio surgical applications.

The application of numerous colossal permittivity (CP, > 103) materials was limited on account of relatively higher dielectric loss (>0.05). In this work, the xwt% B2O3 (x = 0, 0.5, 1, 2, 4) adding Ti0.99(Eu0.5Nb0.5)0.01O2 (TENO-xwt% B2O3) ceramics were prepared by a traditional solid state method. SEM analysis indicated that the average grain sizes obviously decreased by adding B2O3 and the low dielectric loss corresponding with the colossal permittivity were obtained in all samples. Especially, the higher permittivity of 4.1 × 104 and lower dielectric loss of 0.012 were achieved while x = 2 at 1 kHz and room temperature respectively, accompanying with good temperature stability ranging from −55 °C to 200 °C. Moreover, the formation mechanism of excellent dielectric properties was studied on the basis of analysis of the SEM, complex impedance and electric modulus. The results showed that the addition of B2O3 refined the grains and strengthened the interface effect. Furthermore, the B2O3 existing in the grain boundary formed barrier layer which hindered the long range motion of electrons.

In this study, calcium borosilicate (CaO-B2O3-SiO2, CBS) glass-ceramics were fabricated using chemically pure CaO, SiO2, and B2O3 as raw materials. Differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and electrical measurements were conducted to explore the effect of titanium dioxide (TiO2) doping on crystallization, microstructure, and dielectric properties of CBS glass-ceramics. Furthermore, the influence of sintering temperature and sintering schemes on crystalline phases of CBS glass-ceramics was systematically investigated. Results showed that the increase of TiO2 content led to the reduction in sintering temperature of CBS glass-ceramics and promoted the precipitation of wollastonite crystal phase. For instance, with the increase of content of TiO2 from 0 to 3 wt%, transition temperature and crystallization temperature were reduced by 12.9 and 27.6 °C, respectively. However, excessive TiO2 affected the precipitation of wollastonite crystal phase, destroyed crystal structure, and damaged close arrangement of crystal grains. Moreover, higher TiO2 content was found to weaken dielectric properties of CBS glass-ceramics. In this study, the best molar ratio of ingredients, meeting that of ideal target material, is n(Ca): n(Si): n(B) = 1:1:0.6, with doping mass fraction of 2 wt% of TiO2. After optimal sintering procedure, dielectric constant of the best sample was found to be 1.4 (1 MHz), 1.3 (10 MHz), and dielectric loss was 3.9 × 10−3 (1 MHz) and 3.8 × 10−3 (10 MHz).

Highly dense CaCu3Ti4O12 (CCTO) ceramics co-doped by ZnO and Al2O3 were synthesized by spark plasma sintering (SPS) at 750 °C for 10 min, and then annealed at 1000 °C for 3 h. The homogeneous microstructures were achieved, and the grain size was suppressed to around 2 μm. Dramatically enhanced electrical properties of CCTO ceramics were obtained when 1 mol% ZnO and Al2O3 were co-doped. The breakdown field was improved to 12.13 kV/cm and the nonlinear coefficient was increased to 6.59, accompanying with a low dielectric loss of 0.02 at around 1 kHz, which were ascribed to the elevation of Schottky barrier height from 0.54 eV to 0.80 eV. Comparing with the pure CCTO sample, the activation energy of grain boundary obtained from the impedance spectra increases from 0.64 eV to 0.92 eV. Additionally, the grain and grain boundary resistance were also discussed based on the Cole-Cole plot, from which the grain boundary resistance was found to be increased significantly from 3.8 × 105 Ω to 4.0 × 106 Ω after co-doping.

Dielectric losses could be tuned by controlling the compositions and specific structural units. Herein we demonstrate that the complex permittivity of Fe@Graphite nanocapsules at gigahertz can be effectively enhanced up to ∼150% by a simple annealing procedure. Experimental results reveal that it is originating from the intrinsic polarization of atomic-scale oxygen-carbon complexes, which is ascribed to the formation of the substitutional oxygen in highly defective graphitic layers. The present study opens up a new avenue for optimizing electromagnetic loss performances of materials and provides an insight to atomic-scale structural configuration of dielectric polarizations.

Energy storage capacitors have gained much attention for their potential energy storage applications in pulse power system. In this paper, Ba0.3Sr0.7TiO3 (BST) crystallite thin films were prepared on Pt/Ti/SiO2/Si(100) substrates using a sol-gel method at different annealing temperatures from 650 to 850 °C. The films have a crystallite structure, in which amorphous phase forms a three-dimensional network structure and BST tiny grains are wrapped in it. The effects of annealing temperature on the phase structure, morphology, energy storage and dielectric properties of BST microcrystalline films were investigated. The grain size and the crystallinity increased with the increase of annealing temperature, and both pores and defects were produced on the surface when temperature reaches up to 750 °C. When annealing temperature increases, the breakdown strength and energy storage density increased initially, followed by an decrease. The optimal energy storage performance was achieved in the sample with the energy storage density of 31.6 J/cm3 at 3.0 M V/cm, while annealing at 700 °C. Moreover, the sample also exhibited a moderate dielectric constant (60) and a low dielectric loss (0.001).

In this work, nominal composition (1-x)BaTiO3-xBi(Zn0.5Y0.5)O2.75 [abbreviated as (1-x)BT-xBZY, (x = 0.05, 0.1, 0.15, 0.2, 0.25)] ceramics were prepared by solid-state reaction method, and sintered in reducing atmosphere. Effect of introducing BZY on the structure, dielectric and insulating properties of BT was investigated. XRD results demonstrated that the unit cell volume of (1-x)BT-xBZY ceramics expanded with the addition of BZY, accompanied with the transformation from tetragonal to pseudo-cubic phase when x ≥ 0.05. Electrical properties measurement showed that the dielectric-temperature stability and insulating properties of (1-x)BT-xBZY ceramics were effectively improved by BZY addition, where the optimum performances were achieved at x = 0.15, with the dielectric constant of 1362 and dielectric loss of 1.4%, and resistivity of 5.5 × 1012 Ω cm at room temperature, meeting the standard of X8R specification for MLCC application. The feasible mechanism of improved anti-reduction properties for (1-x)BT-xBZY ceramics was investigated by employing X-ray photoelectron spectra (XPS) and thermally stimulated depolarization current (TSDC) testing techniques, where the formation of defect dipoles [2YTiˈ- V O .. ] and the deoxidation of Bi ion were revealed and considered to be responsible for the anti-reduction behavior.

The development of high dielectric loss and magnetic loss for radar absorbing material is a long-term pursuing and under a close scrutiny. Most of the researches have been focused on exploring absorber materials with good absorption performance and at the same time with a good electrical conductivity. To develop a new absorber material will also have significant impacts on boosting the dielectric loss and magnetic loss. Herein, 3D spherical NiCo2S4 (NCS)-based composite has been fabricated via a mild, simple and useful hydrothermal strategy and the electromagnetic wave absorbing properties have been investigated through comparison among NCS, acidified carbon nanotubes (a-CNT)/NCS, reduced graphene oxide (r-GO)/NCS and r-GO/a-CNT/NCS. The experimental results show that the optimal concentration of NiSO4·6H2O to synthesize the composites is 6 M. Furthermore, the frequency bandwidth has been broadened and the maximum absorption peaks have been increased after adding the modified agent. The maximum frequency bandwidth of r-GO/a-CNT/NCS is 5.1 GHz below −5 dB and 2.7 GHz below −10 dB respectively, the maximum absorption peak is −35.8 dB at 8.1 GHz.

The CaMoO4 was added into La(Nb0.9V0.1)O4 ceramics by solid state reaction method to adjust the temperature coefficient of frequency (TCF) values. The series of (1−x)La(Nb0.9V0.1)O4-xCaMoO4 (0.05 ≤ x ≤ 0.5) ceramics were sintered at 1060–1180 °C and found to possess permittivity (er) = 10.38–17.73, Q × f = 31,820–76,570 GHz (Q = 1/dielectric loss, f = resonant frequency lying between 8.5 and 9 GHz), and TCF = −26.3 ∼ +160.7 ppm/°C. The structures of ceramic samples changed from monoclinic fergusonite to tetragonal scheelite continuously at x = 0.20 along with the shift of TCF values from positive to negative. The best microwave dielectric properties with er = 15.71, Q × f = 76,310 GHz (at 8.825 GHz), and TCF = − 26.3 ppm/°C were obtained in 0.8La(Nb0.9V0.1)O4-0.2CaMoO4 ceramics sintered at 1160 °C and these ceramics might be good candidates for microwave devices.

The BiMeO3-PbTiO3 (Me = Sc3+, In3+, Yb3+) systems are thought to have remarkable advantage in their Curie temperature in comparison with other perovskite ferroelectric materials. Among them, the BiScO3-PbTiO3 (BS-PT) solid solution with high Curie temperature (450 °C) and excellent piezoelectric coefficient is promising candidate for high temperature sensors and transducers application. Herein, we reported the effect of the addition of Pb(Mn1/3Sb2/3)O3 (PMS) on the electrical properties of BS-PT ceramics. The results showed that the temperature stability of BS-PT ceramics can be improved by the addition of a small quantity of PMS based on conjoint analysis of the temperature dependence of P-E hysteresis loops, leakage current density and kp. While the 0.03PMS-0.33BS-0.64 PT ceramics exhibited the optimal electrical properties at room temperature with the piezoelectric coefficient (d33) of 300 pC/N, the Curie temperature (TC) of 365 °C, the coercive field EC of 17 kV/cm, the dielectric constant er of 1346, and dielectric loss tanδ of 0.74%. It was concluded that the temperature stability of the piezoelectric properties and the relaxor behavior were enhanced by the addition of PMS.

In this study, various amounts of BaTiO3 ceramics (BTO) were introduced into Ni0.15Cu0.24Zn0.61Fe2O4 (NCZF) via solid-state reaction method and sintered at 920 °C with 2 wt% Bi2O3 addition. Obviously, the magnetic properties were affected violently but dielectric behaviors were improved, and the variations showed great regularity. We obtained composite materials with well magnetic and dielectric properties which can meet different design requirements of devices. To be specific, phase distribution and composition, microstructure morphology, magnetic and dielectric properties of these composites were systematically investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), and impedentiometry. XRD analysis results proved that the biphase (ferrite phase and ceramic phase) was produced successfully, whereas SEM micrographs revealed that grain size decreased with the content of BTO ceramic. Magnetic properties, such as saturation magnetization (4πMs), coercivity (Hc), permeability (μ′), and quality factor (Q) can vary with the amount of BTO ceramics. By adding BTO to NCZF, electrical properties, such as dielectric constant (e′) and dielectric loss (tan δ) were remarkably improved. Indeed, when the content of BTO ceramics varied from 5 wt% to 10 wt%, so-prepared composites possess outstanding electromagnetic properties (μ′ > 50.5, Q > 60, e′ ≈ 23.8, tan δ

SiCf/SiC composites have been recognized as an ideal structural and microwave absorbing materials, however the use of SiCf/SiC composites still restricted at the stage of laboratory research due to their poor mechanical and microwave absorbing properties. In this study, both the bending strength and the complex permittivity for microwave absorbing purpose were successfully improved with the addition of aluminum fillers during the Precursor Infiltration and Pyrolysis (PIP) process of SiCf/SiC composites. The effects of aluminum powder content on the microstructural evolutions of polycarbosilane (PCS) derived SiC matrix, mechanical and dielectric properties of composites were investigated. The results confirm that the flexural strength of composite reaches the maximum value of 317 MPa when the aluminum content is 10 wt% owing to the higher densification and the generation of β-SiC and Al4C3. The values of e′ and e′′ can be reduced to suitable levels with good impedance matching and dielectric loss when the aluminum content is 5 wt% attributed to the reduction of free carbon in the matrix. Furthermore, the reflection loss values of composites can be as low as −56 dB and the optimal bandwidth below −10 dB is 3.4 GHz when incorporating 5 wt% aluminum powders.

Ilmenites, which find enormous applications, because of their high relative permittivity and modest dielectric losses can have their efficiency and practical applicability enhanced by incorporation of ferroelectricity and multiferroicity in them. In our present work, ferroelectricity and magneto-electric (ME) effect is induced in the non-ferroelectric ilmenite FeTiO3 by modifying it with bismuth and lead titanate. The structural, micro-structural, electrical, ferroelectric and magneto-electric effect of the studied compounds were investigated using x-ray diffraction, field emission scanning electron microscope, phase sensitive impedance analyser, polarization–electric field hysteresis loop measurements and ME set up respectively. The analysis of I ∼ V characteristics curve shows that the modification results in the decrease of leakage current of the parent compound by three order of magnitude. Thus, in the present work, it is shown that the modifications not only induce ferroelectricity and multiferroicity in the parent compound, but also reduces the leakage current drastically.

The search for colossal dielectric constant materials is imperative because of their potential for promising applications for the areas of device miniaturization and energy storage. In this work, (Nd0.5Nb0.5)xTi1-xO2 ceramics is prepared via the solid-state reaction route. The microstructure, crystal structures, and dielectric properties of (Nd0.5Nb0.5)xTi1-xO2 ceramics are investigated. It is proved that schottky barrier exists at grain boundary by measuring impedance spectrum of different DC biases and C-V curve. The grain boundary characteristics of the ceramics are studied. It is found that the proper second phase is beneficial to increase the grain boundary resistance and restrain the long range movement of electrons, so that the material keeps low dielectric loss and improves the temperature stability. But too much of second phase will deteriorate performance due to excessive space charges. In addition, all the (Nd0.5Nb0.5)xTi1-xO2 ceramics displays a colossal dielectric constant (>104), especially a high dielectric constant (2.55 × 104) and low dielectric loss (0.023) at 1 kHz and room temperature which can be obtain in (Nd0.5Nb0.5)xTi1-xO2 ceramic with x = 3%. The dielectric properties of (Nd0.5Nb0.5)xTi1-xO2 ceramics can be explained by internal barrier layer capacitor (IBLC) model, which can be optimized by balancing grain size, barrier height and barrier width.

In this study, Li2Mg4Zr0.95(Mg1/3Ta2/3)0.05O7 (LMZT) ceramics were prepared via the conventional solid-state method. A cubic rock-salt structure with space group of Fm-3m was observed in all samples. Excellent microwave dielectric properties of er = 12.68, Q × f = 190,403 GHz and τf = −20.64 ppm/°C were achieved for LMZT ceramic at 1500 °C. The variations in microwave dielectric properties were systematic investigated by polarizability, packing fraction and infrared spectrum. The complex dielectric loss was calculated from the fitting data of far infrared spectrum, which was in good agreement with the measured value. Moreover, the sintering characteristics, phase composition and microwave dielectric properties of LMZT-x wt.% LiF ceramics were researched. Dense microstructure could be gained at 1000 °C for 4 and 5 wt% LiF-doped LMZT ceramics due to liquid-phase sintering. The LMZT ceramics with 4 wt% LiF addition possessed excellent microwave dielectric properties: dielectric constant of 14.35, quality factor of 130,1030 GHz, temperature coefficient of resonant of −30.24 ppm/°C at 1000 °C.

Ferroelectric 0.7BiFeO3-0.3PbTiO3 (BFO-PT) thin films were deposited on LaNiO3 (LNO) coated stainless steel (SS) substrates by the sol-gel method. XRD results indicate that both LNO and BFO-PT thin films have the perovskite structure and the film crystallinity is improved with increasing the LNO thickness. The dielectric loss of BFO-PT thin films is reduced significantly with addition of LNO buffer layers, achieving about 4% at the frequency of 1 kHz, much lower than that of >20% for BFO-PT thin films directly deposited on SS substrates. BFO-PT thin films reveal the strong ferroelectricity with remnant polarization (Pr) of about 35 μC/cm2 for LNO of 390 nm. Moreover, addition of LNO buffer layers mitigates the polarization deterioration after the 1.33 × 108 switching cycles resulting in the improved anti-fatigue properties of BFO-PT thin films. Our results indicate that BFO-PT/LNO multilayer thin films on SS substrates maintain excellent dielectric and ferroelectric properties.

Er-doped K0.5Na0.5NbO3-SrTiO3 transparent ceramics were fabricated by traditional pressureless sintering. The dual effects of Er3+ and SrTiO3 contents on the microstructures, optical transparencies and optoelectronic properties of the ceramics were investigated. The introduction of Er3+ and Sr2+ results in decreasing grain size and generating cation vacancies, affecting the density and uniformity of the ceramics. The ceramics exhibit superior transmittance: T ∼55% in the visible region (760 nm) and ∼75% in the infrared region (2000 nm), which is dependent on optical band gap energy. In terms of electrical properties, the ceramics also possess relaxor-like characteristics, low dielectric loss and suitable piezoelectric constants. Due to Er3+, the ceramics exhibit composition-tunable green and red up-conversion photoluminescence emissions, whose intensities are related to the crystal symmetry. Combined with good optical and electrical properties, the ceramics open up potential applications in the electrical/optical interdisciplinary field, such as visible displays, solid-state lasers and transparent electronic devices.

Magnetoelectric effect is directly measured in the Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics, which is rarely reported in tungsten bronze ceramics. Besides, the effects of Sm-substitution on the crystal structure, dielectric, ferroelectric and magnetic properties have been systematically studied. XRD Rietveld refinement confirms all the ceramics to be single phase with space group of P4bm. With the increase of x, Ba4(SmxLa1-x)2Fe2Nb8O30 ceramics transform from paraelectric to ferroelectric. The compositions of x = 0.9, 0.95 and 1 show first-order ferroelectric phase transitions above room temperature. Compared to composition x = 0, the dielectric constant of other compositions exhibits frequency stability and the dielectric loss decreases apparently at room temperature. The ferroelectricity improves with increasing x, which can be ascribed to the increased A2-A1 ionic radius difference. Meanwhile, the magnetic hysteresis loops are obtained for some compositions. All the results approve Ba4(SmxLa1-x)2Fe2Nb8O30 (x = 0.9, 0.95, 1) ceramics as room temperature multiferroic materials with intrinsic magnetoelectric effect.

This research work focuses on the dielectric and magneto-capacitance behavior of (1-X) BaTiO3 – X (CoFe2O4/ZnFe2O4/Co0.5Zn0.5Fe2O4) (where X = 20, 30 and 40 wt%) composites and the results are compared among prepared composites based on the type of ferrite used. The ferrite based magneto-dielectric composites have been prepared via auto combustion derived in-situ synthesis method. The sintered (1150 °C) composites have homogeneous microstructure in which both BaTiO3 and ferrite phases along with barium hexa-ferrite (BaFe12O19) are nearly same in size. In addition to homogeneous microstructure, the concentration and the intrinsic properties of ferrites along with BaFe12O19 has noticeable effect on the permittivity, dielectric loss and P-E hysteresis loop of individual composites. Also, magneto-capacitance response either in the positive or negative direction in the homogeneous microstructure of BaTiO3-ferrite composite systems depends on the intrinsic properties as well as the concentration of the ferrite and barium hexa-ferrite phases. The origin of magneto-capacitance of these composite systems was discussed based on magneto-impendence versus frequency curve and Cole-Cole plot. Negative magneto-capacitance percentage and having highest (−8.4%) among prepared composites was observed in the cobalt ferrite based composites. Positive and negative magneto-capacitance responses were observed in both zinc and cobalt-zinc ferrite based composites. The improved magneto-capacitance in these composite systems may be suitable for different applications.

SrTi1-x(Zn1/3Nb2/3)xO3 ceramics with various defect concentration were designed and prepared via solid state reaction method, the close relationships between defect structure and dielectric behavior of were investigated in detail. High permittivity (∼9100) and low dielectric loss (∼0.03) are achieved at an optimum doping concentration (x = 0.015) due to the enhanced local polarization, while the dielectric properties deteriorate because of the increasing self-compensation as the impurity concentration continuously increases. Further investigation shows that, the giant permittivity is owing to the defect polarization, including off-center Zn2+/Ti3+, combination center ( N b T i · − e ′ ∙ T i 4 + ) and defect dipoles ( T i 3 + − V O · · − T i 3 + ) as well as the contribution from interface polarization, low dielectric loss results from the localization of electron by the defect dipoles/clusters. These findings provide the requisite data and idea for defect design in complex perovskite materials.

We investigated the magnetic and dielectric properties of perovskite HoCr0.5Fe0.5O3. The coexistence of various magnetic interactions resulting from disordered transition-metal ions leads to an intricate temperature dependence of the magnetic properties. From the examination of the temperature dependence of magnetic susceptibility and heat capacity, an antiferromagnetic order of Cr3+/Fe3+ moments arises below TN = 304 K and a spin reorientation transition occurs at TSR = 170 K. In addition, an antiferromagnetic order of Ho3+ spins emerges at THo = 18 K. Based on the sufficiently low dielectric loss below 150 K, excluding the influence of extrinsic effects, a highly nonlinear variation in the isothermal dielectric constant, with a similar hysteretic behavior of the magnetic-field derivative of magnetization, is observed. In comparison to the lack of a noticeable magnetodielectric effect in YCr0.5Fe0.5O3, the strong correlation between magnetic and dielectric order parameters in HoCr0.5Fe0.5O3 suggests the important role of magnetic rare-earth Ho3+ ions. Our results accompanied by intricate magnetic correlations in the disordered HoCr0.5Fe0.5O3 are expected to trigger fundamental and applied research on magnetic materials through the scope of specific magnetic characteristics in disordered perovskites.

A scheelite structured [Ca0.25(Nd1-xBix)0.5]MoO4 (0.2 ≤ x ≤ 0.8) ceramics were prepared via solid state reaction method. All the ceramics can be well densified below 780 °C. As x value increased from 0.2 to 0.8, microwave dielectric permittivity increased from 14.0 to 27.8, Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) value decreased from 42,000 GHz to 19,000 GHz, and TCF shifted from −50 ppm/oC to +18 ppm/oC. The best microwave dielectric properties with permittivity between 23.54 and 23.56, Qf value between 24,000 GHz–21,000 GHz and TCF value ∼ −8 ppm/oC in wide temperature range 25 °C–130 °C were obtained in x = 0.6 ceramic. This work showed that Bi played an important role to modify the TCF from negative to positive value in scheelite materials and this result further accelerate the application of scheelite materials in low temperature co-fired ceramics (LTCC) technology.

The effect of sintering atmosphere on the microstructure and dielectric properties of Sr0.985Ce0.01TiO3 were investigated in this article. The sample sintered in nitrogen achieves a colossal permittivity (∼12655) and ultralow dielectric loss (0.006) at room temperature and 1k Hz. XRD results reveal that all the samples belong to P m 3 ¯ m space group and no secondary phase is detected. It can be verified by XPS measurement that the nitrogen sintered sample has the highest Ti3+ content. Five dielectric relaxations can be observed in the dielectric spectroscopy in the test temperature range from −130–500 °C, which can be attributed to the existence of Ti3+ ions, oxygen vacancies and the other associated defect clusters. Moreover, the off-center Ti3+ ions make a certain contribution to the high permittivity. The ultralow dielectric loss at room temperature could be ascribed to the formation of defect clusters in the samples sintered in air and nitrogen. These defect clusters which associated with the oxygen vacancy, such as T i 3 + − V O .. − T i 3 + and V S r " − V O ¨ are able to localize charge carriers and restrain the motion and ionization of oxygen vacancies.

The polycrystalline sample BaTi0.5 (Co0.33 Mo0.17) O3 was synthesized by the sol-gel method. The effect of replacing titanium by cobalt and molybdenum on the structural and electrical properties of our compound was investigated. The results of X-ray diffraction (XRD) at room temperature showed a pure tetragonal perovskite. The electrical response was studied by complex impedance spectroscopy over a broad frequency range (30–106 Hz) at different temperatures. The values of ac conductivity were fitted by Jonscher's law σ(ω) = = σ DC + Aω n and supported by the correlated barrier hopping (CBH) mechanism. Complex impedance analysis confirmed the existence of an electrical relaxation in the compound. The dielectric constant and the dielectric loss decreased with the increase in frequency. This behavior can be explained by the presence of the Maxwell–Wagner type of polarization responsible for the electric conduction. The modulus plots were characterized by the Havriliak–Negami (H-N) and the empirical Kohlrausch–Williams–Watts (K.W.W.) functions. The Normalized plot of the imaginary part of modulus indicates that the dynamical processes are temperature independent.

Effects of sintering condition on dielectric properties and microstructure were systematically investigated in (Ag1/4Ta3/4)0.005Ti0.995O2 ceramics. A giant dielectric constant of ∼9831 (1 kHz) and a relatively low dielectric loss of ∼0.041 (1 kHz) were realized at the optimal sintering condition of 1330 °C with a holding time for 10 h. Notably, stable temperature coefficient (within −6.8% to 8.8%) of the dielectric constant at 10 kHz was achieved in a broader temperature range (-200–200 °C), which shows superior temperature stability of our sample than the application requirements (−55–200 °C and Δer/e25 °C

Sandwich-structured SrTiO3/BiFeO3/SrTiO3 (ST/BF) thin films were prepared via a sol-gel method for energy storage applications. The thin films demonstrated good frequency stability of the dielectric constant within the measured frequency range, low dielectric loss and broad capacitance-temperature variation (25oC-200 °C, ΔC/C25oC≤±6.0%). Through BF layer insertion modulation, the crystallization quality and energy storage density of ST/BF thin films significantly increased in comparison to ST films. In addition, with the increase thickness of BF layers, the breakdown strength and energy storage density decreased. The maximum recoverable energy storage density (Urec of 40.69 J/cm3) with an efficiency of 44.7% at 2.06 MV/cm was obtained within this system. Moreover, compared to simple tri-layered thin films, the Urec value of the thin films with more interfaces was enhanced to 80%. The results indicate that sandwich-structured ST/BF thin films are a cost-effective, potential more efficient option for energy storage fields.

Colossal permittivity (CP) materials have many important applications in electronics but their development is generally hindered due to the difficulty in achieving a relatively low dielectric loss. In this work, based on the electron-pinned defect-dipole and internal barrier layer capacitance (IBLC) theory, we designed to add Bi2O3 to (Eu0.5Nb0.5)0.01Ti0.9O2 (ENTO) ceramics to obtain high performance CP materials. The dielectric loss can be reduced down to 0.017 at 1 kHz and room temperature, while the permittivity is kept at a relatively high value (2.7 × 104). At the same time, the temperature and frequency stability can also be improved. More importantly, the mechanism of decreasing dielectric loss is studied. It is finding that the decrease of dielectric loss is closely associated with the enhanced localized behavior of conduction process at grain boundary. The addition of Bi2O3 can increase the grain boundary resistance and grain-boundary activation energy of the ceramics, which make the conductive behavior of the grain boundaries more difficult, resulting in decreasing the dielectric loss and improve the temperature stability of the ceramics.

Magnetic Co-Ni-P nano-alloys were successfully prepared as microwave absorbers. Unfortunately, the poor dielectric properties severely restricted their microwave absorption performance. With the goal of high microwave absorption efficiency, one dimensional (1D) Co-Ni-P/SiC nanowire composites were firstly fabricated by means of an easy electroless plating method. A three dimensional (3D) conductive network can be constructed by the 1D composites. Results demonstrated that the 3D conductive network has significant effects on improving the dielectric loss of absorbers. The minimum reflection loss of the optimized composites can reach −45 dB at 12.5 GHz with a thickness of only 1.5 mm owning to their suitable impedance matching and multiple loss mechanisms. This work proposed a facile route to prepare 1D magnetic absorbers with higher absorption efficiency and their electromagnetic property and microwave absorption were also studied in detail.

To investigate the effect of different pH values (pH = 1, 3, 5, 7) of a solution used to prepare CaCu3Ti4O12 (CCTO) ceramics on the microstructure and dielectric properties of the resultant ceramics, the acid regulator in the solutions was replaced with an alkaline regulator, ammonia water, and CCTO ceramics were prepared through a sol-gel method. The data show that the dielectric constants of the as-prepared samples maintained relatively high values in the frequency range from 1 to 107 Hz. In addition, the dielectric loss decreased to 0.028 at 103 Hz for the sample prepared at pH = 5. Moreover, the results reveal that the grain size, porosity and content of the CuO phase at the grain boundaries of the CCTO ceramics varied with the pH value. Our results indicate that using an alkaline regulator to adjust the pH value of the synthesis solution is an effective method for reducing the dielectric loss of CCTO ceramics.

Novel core@shell@shell structured carbonyl iron powder (CIP)@SiO2@ Mn0.6Zn0.4Fe2O4 ferrite composites having great microwave absorption characteristics were successfully synthesized using chemical co-precipitation. The microstructure, morphology and microwave absorption performance of CIP@SiO2@Mn0.6Zn0.4Fe2O4 ferrite composites were systematically investigated. The results show that both coating layers of SiO2 and Mn0.6Zn0.4Fe2O4 are uniform and fine. The prepared CIP@SiO2@Mn0.6Zn0.4Fe2O4 composites in this study display better dielectric loss and frequency characteristic at high frequency than CIP, CIP@SiO2 and CIP@Mn0.6Zn0.4Fe2O4. The results of electromagnetic parameters also indicate that the enhanced microwave absorption performance primarily originates from the substantial contributions of magnetic loss to reflection loss. The optimal value of reflection loss of CIP@SiO2@Mn0.6Zn0.4Fe2O4 having the thickness of 2 mm can reach up to −44.24 dB at 11.57 GHz as well as the bandwidth (RL ≤ −10 dB) from 9.04 to 16.16 GHz among the frequency range from 2 to 18 GHz. In addition, the greatly enhanced microwave absorption performance is attributed to good wave impedance matching, high attenuation constant, multi-relaxation processes and multiple interfacial polarization.

To effectively optimize electromagnetic (EM) wave absorption performance and reduce the reflection at the absorbent-air interface, the absorbents coupling magnetic/dielectric loss components to construct heterogeneous interfaces are urgent. Herein, we report a facile method for preparing a unique (TiC/Ni)@C ternary composite. The incorporation of Ni into TiC/C matrix to form heterogeneous interface not only ameliorates impedance matching, but also introduces the additional interface polarization for tuning dielectric loss capacity. Comparing with the weak absorption performance of TiC@C composite, the minimum reflection loss (RL) value of (TiC/Ni)@C composite can reach up to −43.4 dB at 7.0 GHz with the 3.4 mm thickness, and the effective bandwidth of RL below −10 dB can be up to 5.1 GHz at the 1.8 mm thickness. The results reveal that the efficient synergistic effect between magnetic Ni and dielectric TiC/C plays a more important role for the absorption performance, comparing to the merely strong dielectric loss of TiC@C composite.

Three-dimensional (3D) carbon networks decorated with Fe3O4 nanoparticles as lightweight and broadband electromagnetic (EM) wave absorber were in-situ prepared via a simple and large-scale method, combining freeze-drying and high-temperature calcination processes. SEM and TEM results show that 3D carbon network/Fe3O4 (3DC/Fe3O4) composites have interconnected 3D porous carbon networks with submicrometer-sized macropores, and the Fe3O4 nanoparticles are distributed uniformly on the 3D carbon networks. The EM wave absorption performance of 3DC/Fe3O4 can be tuned by changing Fe3O4 contents. The 3DC/Fe3O4 with about 38.2 wt% Fe3O4 exhibits excellent lightweight and broadband EM wave absorption property. The effective absorption bandwidth can reach up 5.95 GHz (11.2–17.15 GHz) at the thickness of 3.0 mm with only 20 wt% filler loading. The minimum RL of −37.8 dB was obtained at 6.95 GHz. The excellent EM wave absorption capability of 3DC/Fe3O4 can be ascribed to good impedance matching, strong dielectric loss ability and unique 3D porous structure. This work demonstrates that the 3DC/Fe3O4 with light weight, broad absorption bandwidth and large-scale production potential can be a promising absorber for practical application.

Well-ordered core/shell/shell-like Fe3O4@SiO2@PPy microspheres with prominent electromagnetic microwave absorption performance were successfully obtained by microemulsion polymerization method. The morphology, crystal form, functional group, magnetism and microwave absorption properties were investigated. The tailored shell thickness can be tuned from 20 to 60 nm (including SiO2 layer) via changing the molar ratio of Fe3O4@SiO2 to Pyrrole. The absorption peak positions gradually move to low frequency with increment of coating thicknesses. The minimum RL reached −40.9 dB at 6 GHz with the coating thickness of 5 mm. The effective absorption bandwidth could reach 6.88 GHz from 11.12 to 18 GHz, completely covering the whole K (12–18 GHz) band. Meanwhile, it showed excellent wave absorption in 4.4–18 GHz with different coating thickness. The perfect electromagnetic wave absorption properties could be attributed to the dielectric loss from the special core/shell/shell microstructure and natural resonance from the Fe3O4 microspheres. These newly prepared Fe3O4@SiO2@PPy microspheres might be considered as prospective nominees for highly efficient microwave absorption materials with tailored nanostructures.

With the rapid growth in the use of wireless electronic devices, society urgently needs electromagnetic wave (EMW) absorbers with light weight, thin thickness, wide effective absorbing bandwidth and strong absorbing capacity. One kind of the most attractive absorbers is magnetic carbon composites. Here, we successfully synthesized porous carbon matrix with inlaid Fe3C/Fe3O4 micro-particles (CFF) by in-situ carbonization of pre-prepared Fe3O4/wood shavings composites at 1000 °C. In advance, the magnetic wood shavings were prepared by in-situ chemical coprecipitation followed by two-step atmospheric impregnation of Fe2+/Fe3+ mixture and NaOH solution, successively. Compared with natural wood shavings and magnetized shavings, the EMW absorption properties of CFF is greatly improved by the phase transformation from amorphous carbon to graphite-like carbon through the carbonization procedure. In details, CFF possesses a minimum RL value of −26.72 dB at 10.52 GHz with a matching thickness of 3.15 mm and a wide response bandwidth of 12.93 GHz covering from 5.07 GHz to 18 GHz. This excellent absorption performance is proved to be due to the continuous covering of Fe3C/Fe3O4 hybrids on the surface of the porous carbon matrix, permitting optimal impedance matching, the strongest dielectric loss and the optimal magnetic loss. Moreover, the dipole relaxation polarization brought out by the generated defects acting as the dipole center, together with the interface polarizations at C Fe3C and Fe3C Fe3O4 interfaces, are positive to improve the microwave absorption performance.

The Ni0.6-xLi0.5xZn0.4Fe2+0.5xO4 (x = 0.0, 0.2, 0.4, 0.6) ferrites prepared by the sol-gel auto-combustion method have been characterized by XRD, XPS, SEM, FTIR, VSM, impedance analyzer for various physical properties. The analysis of Fe 2p photoelectron spectra reveals that the valence state of iron ion is only trivalent. The cation distributions obtained from Rietveld refinement of XRD data show that Li+ ions occupy only octahedral sites, while Ni2+, Zn2+ and Fe3+ ions are distributed in both tetrahedral and octahedral sites. The increase in bond angles ( θ 1 and θ 2 ) suggests the enhancement of A-B super exchange interaction which is further confirmed by the decreased αY-K angles and increased Curie temperature (Tc). All observed absorption bands in the FTIR spectrum have been explained by the vibrations of tetrahedra and octahedra. The Debye temperature ( θ D ) and the elastic moduli (bulk modulus B, rigidity modulus G and Young's modulus E) evaluated through FTIR spectroscopy decrease with the increase of Li+ and Fe3+ ions contents. The saturation magnetization (Ms) decreases firstly and then increases with x increasing. The initial permeability (μi) increases monotonically with x. The value of dielectric constant (e′) sharply decreases at lower frequency and become almost stable at higher frequency for all samples, indicating the semiconductor behavior of the ferrites. Compared with the Li-Zn ferrite, the Ni-Zn ferrites has lower dielectric loss tangent (tan δe) and magnetic loss tangent (tan δm) at higher frequency. This work represents the first exploration of the correlation of structure with elastic, thermal and magnetic and electrical properties of Ni-Zn-Li ferrites.

This paper reported the dielectric and structural characterization of composites formed by mixture of BiVO4 and TiO2 and applications in microwave range. The composites were formulated by addition of TiO2 (15, 30, 45 and 60 wt %) in BiVO4. X-Ray Diffraction (XRD) was used in structural characterization. The dielectric properties, temperature coefficient of resonant frequency (τf), dielectric permittivity (e) and dielectric loss (tan δ), were measured and the results confirm that the TiO2 addition improves the thermo-stability of the composites with values varying from −244.03–246.12 ppm.0C−1. The dielectric properties varied with TiO2 composition (31

Herein we studied the effect of Gd-Zn substitution on structural and dielectric properties of Ca0.5Ba0.5-xGdxZnyFe12-yO19 (x = 0.00, 0.04, 0.08, 0.10; y = 0.00, 0.40, 0.80, 1.00) synthesized by sol-gel autocombustion method. The prepared compounds were examined via XRD, SEM along with dielectric and electrical properties. Peak patterns of XRD analysis revealed the pure phase formation of M-type hexagonal ferrite. As concentration of Gd-Zn increases the lattice parameter were also found to increase. The scanning electron microscopy investigations revealed that the size of grain lies in between 1.19 and 0.58 μm and the size of grains are reduced on increasing the substitution of Gd-Zn concentration. It is clear that the value of resistivity increases from 6.47 × 10 9 Ω -cm to 2.40 × 10 10 Ω –cm with increasing Gd-Zn concentration. The alteration in AC conductivity as a frequency function might be explained on the ground of Maxwell–Wagner model and of Koop's Phenomenological theory. The inspected alteration in dielectric constant could be illustrated on the behalf of hopping conduction between Fe2+ and Fe3+ and space charge polarization. The dielectric loss dispersion inspection is because of Koop's phenomenological theory and Maxwell–Wagner interfacial sort polarization.

In this paper, nonstoichiometric cobalt ferrite (Co0.8Fe2.2O4) and reduce graphene oxide (rGO) nanocomposites were synthesized by a facile one-pot hydrothermal method. The effect of rGO addition on the structure, morphology and magnetic properties of Co0.8Fe2.2O4/rGO nanocomposites was systematically investigated. Herein, owing to adjustable microstructure as well as the synergistic effects of Co0.8Fe2.2O4 and rGO, the electromagnetic (EM) wave absorption property of Co0.8Fe2.2O4/rGO nanocomposites can be well tunable by changing the addition amount of rGO. In comparison to pure Co0.8Fe2.2O4 ferrites, the introduction of rGO can greatly enhance EM wave absorption properties. Notably, the composite with the addition amount of 10 mg GO exhibits the minimum reflection loss (RL) of −51.2 dB at 11.4 GHz with the effective absorption bandwidth (≤−10 dB) 5.7 GHz when the absorber thickness is 2.1 mm. Meanwhile, when the addition amount of GO is 20 mg, a super-broad effective absorption bandwidth of the corresponding sample reaches 7.2 GHz from 10.8 to 18 GHz with a thickness of 2 mm. Owing to the good impedance matching and the synergistic effect between magnetic and dielectric loss, the as-synthesized Co0.8Fe2.2O4/rGO nanocomposites can be regarded as a new candidate for the lightweight EM wave absorber.

Carbon nanotubes (CNTs)/Indium tin oxide (ITO) composites have been successfully synthesized via coprecipitation and calcination processes. The effects of calcination temperature on the electromagnetic properties of the CNTs/ITO composites were investigated. The real part of the permittivity and the dielectric loss increase with increasing calcination temperature, which can be attributed to the enhanced dielectric relaxation and space charge polarization. The CNTs/ITO composites synthesized at 600 °C can achieve lower reflection loss (RL) value at the thickness of 2–4 mm, while the composites synthesized at 850 °C exhibit broader bandwidth, corresponding to an RL value below −10 dB at a thin coating thickness of 1–1.5 mm. The microwave absorption properties of the CNTs/ITO composites at different frequencies can be tuned by controlling the calcination temperature and the thickness of the absorbing coating. The dielectric loss, quarter-wavelength cancellation, and well-matched characteristic impedance in the air-absorber interface are believed to contribute to the superior microwave absorption performance of the composites. The effects of the secondary phase ITO on the electromagnetic properties of the CNTs/ITO composites were also discussed in this study.

Silicon-boron carbonitride ceramics (SiBCN) containing various contents of silicon carbide nanowires (SiCnw) were fabricated via chemical vapor infiltration. The effects of SiCnw content on the morphology, microstructure, phase composition, dielectric and electromagnetic wave (EMW) absorption of the composite ceramics were investigated. Randomly oriented SiCnw contributes to the formation of a conductive network; this leads to an increase in the electrical conductivity. With the increase of the SiCnw content, the dielectric constant and the dielectric loss linearly increased from 3.7 to 0.05 to 4.2 and 0.39, respectively. For the maximum SiCnw mass fraction of 3.8 wt%, the reflection coefficient of composite ceramics attained its minimum value of −15 dB in the X band and the effective absorption bandwidth was 2.88 GHz. After the oxidation, the composite ceramics still had a relatively high dielectric loss. The SiCnw-SiBCN composite ceramics exhibited excellent EMW absorption, indicating their great potential as high-temperature microwave absorption materials.

Aiming at the disadvantages of high cost, complex processes, and low yield of carbon-based microwave absorbing materials. In this study, Co/C fibers were successfully prepared by using low-cost cotton as carbon source. The synthetic route was a flexible two-step approach consisting of immersion and subsequent carbothermal reduction in N2 atmosphere. By means of controlling the Co(NO3)2·6H2O concentration and calcination temperature, Co nanoparticles with different loading amount and particle size were uniformly dispersed along the cotton-based carbon fibers. The Co loading amount, calcination temperature, and filling rate on electromagnetic parameters and microwave absorption performance were systematically studied. Among the Co/C fibers obtained at different Co(NO3)2·6H2O concentration and calcination temperatures, the Co/C fibers synthesized at 600 °C with 0.5 M Co(NO3)2·6H2O exhibited the best microwave absorption performance. The reflection loss (RL) values less than −10 dB were obtained in the frequency range of 11.3–18 GHz, which covered the entire Ku-band (from 12 to 18 GHz). Such excellent microwave absorption performance was attributed to the synergistic effect of dielectric loss, magnetic loss, and good impedance matching. Owing to the characteristics of cost-effective synthetic strategy, low density, and good microwave absorption, the Co/C fibers are highly promising as economic and broadband microwave absorbent.

LiZn1-xMxNbO4 (M = Co, Ni) (x = 0–0.06) systems were fabricated by a facile solid-state reaction method. Structure and property relationships of spinel structured LiZn1-xMxNbO4 were investigated systematically. Appropriate amount of Co2+ and Ni2+ greatly improved the dielectric loss of LiZnNbO4 ceramics. While, the dielectric loss deteriorated seriously when the doping content exceeded x = 0.02. The origin of dielectric loss in LiZn1-xMxNbO4 ceramics was investigated systematically. Moreover, the theoretical dielectric constant and linear expansion coefficient were calculated on the bases of the crystallographic parameters from XRD refinement. The temperature coefficient of resonant frequency calculated by the P-V theory agreed well with the test values. Due to the small doping content, the change in chemical bonds was negligible. Density became the major factor determining the variation of dielectric constant in LiZnNbO4 ceramics. At last, excellent microwave dielectric properties were obtained: Ts = 1010 °C, er = 15.25, Qf = 107,000 GHz, τf = −63.3 ppm/°C for LiZn0.98Co0.02NbO4 and Ts = 995 °C, er = 14.85, Qf = 104,000 GHz, τf = −61.7 ppm/°C for LiZn0.98Ni0.02NbO4.