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Orthorhombic magnesium niobate is known to exhibit exceptional dielectric and photoluminescence properties. With the intention to evaluate these properties, MgNb2O6 (MN2) was synthesized at 900 °C for 6 h through a two-stage process. The phase examination was done by XRD and Raman spectroscopy. XRD analysis confirmed orthorhombic crystal structure with average crystallite size of 41 nm, approximately. The d-value and (hkl) plane corresponding to highest intensity was examined 2.9486 A and (3 1 1), respectively. Raman spectroscopic analysis clarified various vibration bands of MN2 ceramics. The grain size was assessed close to 87 nm from FESEM analysis considering the grain distribution plot. The microstructure analysis by HRTEM reveal nanoparticles of average size of 41.83 nm. The clear lattice image and prominent spots in SAED confirm crystallinity of prepared ceramics. The PL result of the prepared ceramics at 900 °C indicated blue emission spectrum near 442 nm. The material prepared at 900 °C exhibited band gap of 2.65 eV using diffuse reflectance spectroscopic analysis. The dielectric constant (er) and tanδ were also investigated where er was measured 27.8 and 20.8 for material prepared at 800 and 900 °C, respectively. Low tanδ (dielectric loss) was also noted in present investigation.

Barium sodium niobate Ba2NaNb5O15 (BNN) ceramics with different amounts of BaO-Na2O-Nb2O5-P2O5 (BNNP) glass were prepared via the conventional solid-state method. The effect of glass content on structural, microstructure and dielectric properties of BNN ceramics was investigated. The XRD results showed that no secondary phase was formed after adding BNNP glass. It was found that such additions reduce the average grains size and refine the microstructure of the obtained ceramics. Moreover, the samples exhibited a stable dielectric constant over the temperature range of 25°C–150°C and their dielectric constants were significantly improved. The ceramic with 7.5 wt% BNNP glass content showed a dielectric constant which is more than twice as much as that of pure BNN ceramic, as well as a low dielectric loss less than 5%.

The low temperature solution growth method was adopted for growing semi organic single crystal zinc boro glutrate (ZBG). The surface morphology was investigated by SEM analysis. Analysis of microhardness has been done, measurement of the Vickers hardness number Hv. Dielectric studies show a decrease in dielectric loss and dielectric constant with an increase in frequency and a constant value in the higher frequencies, suggesting that the crystal is also of good optical quality in nature.

Chromium zinc ferrite powder with general formula C r x Z n 1 - x F e 2 O 4 was synthesized by usual co precipitation method. The Phase purity and structural confirmation of the sample were done by XRD technique. The dielectric behaviors, dielectric constant, and dielectric loss were studied as a function of frequency at room temperature. The AC conductivity was determined from the dielectric parameters. The dielectric constant increases with increase of frequency. The Hysteresis curves were measured using vibrating sample magneto meter (VSM), the results showed paramagnetic nature of ferrite material

Pure and 1 mol% thiourea doped potassium hydrogen phthalate single crystals were grown by slow evaporation method. Single crystal XRD confirms the crystalline perfection of the crystal. FTIR studies confirm the presence of functional group. UV–Vis studies reveal the good optical transparency of the crystal. The thermal stability of the crystal was confirmed by thermal studies. The strength of the crystal was determined by Vickers micro hardness studies. The dielectric constant and dielectric loss at various temperatures was determined. The nonlinear optical efficiency of 1 mol% thiourea doped KHP and pure KHP crystal was identified by SHG studies.

Constructing three-dimensional (3D) foam-like structure in magnetic metal/carbon composites is regarded as a promising pathway to reinforce their electromagnetic (EM) functions. Herein, a nitrate-assisted polymer-bubbling strategy is reported for the synthesis of Co/carbon foams, which is simply accomplished by direct pyrolyzing the mixture of polyvinylpyrrolidone (PVP) and cobalt nitrate hexahydrate (Co(NO3)2∙6H2O). Co(NO3)2∙6H2O not only plays as the source of Co nanoparticles, but also accounts for the formation of 3D microstructure through releasing gas. By manipulating the weight ratio of Co(NO3)2∙6H2O to PVP, the chemical composition, microstructure, and EM properties of these composites can be easily regulated. When the weight ratio reaches 1.5, the resultant composite displays good microwave absorption performance, whose reflection loss intensity and effective absorption bandwidth are superior to those of many common Co/C composites. EM analysis reveals that such architecture is greatly helpful to establish cross-linked conductive networks in the wax matrix, resulting in powerful dielectric loss under low absorber loading. Meanwhile, 3D microstructure is also beneficial for multiple reflections that equal to extend the transmission path of incident EM waves. Simple synthesis strategy and desirable properties of these magnetic carbon foams may render them as the low-cost substitute of 3D graphene for the application against EM pollution.

The crystal structure, Raman vibration, chemical bond characteristics, and microwave dielectric properties of Zn1-xCuxWO4 (x = 0–0.15) ceramics prepared by a solid-state reaction were investigated by XRD refinement, Raman spectroscopy, P-V-L theory and XPS. According to the P-V-L theory, the properties of the W-O bond are stronger than those of the Zn-O bond, which makes a major contribution to the dielectric properties. The relative permittivity is mainly affected by the average bond ionicity, and the variations in the dielectric loss and τf are mainly attributed to the lattice energy and bond energy. XPS shows that the presence of Cu+ could produce oxygen vacancy defects, increasing the dielectric loss. Additionally, Raman spectra show that the increasing molecular polarizability causes the Raman shift to move to a low wavenumber, and the changes in Raman intensity and FWHM lead to a decrease in the degree of short-range ordering. Particularly, Zn0.97Cu0.03WO4 ceramics sintered at 925 °C showed satisfactory properties (er = 14.20, tanδ = 1.473 × 10−4 at 9.087 GHz, and τf = −40 ppm/°C), which can potentially be applied to LTCC technology and indicate that Cu substitution can not only reduce the sintering temperature, but also optimize the dielectric properties.

Nowadays, ferrites/carbon fibers have attracted considerable attention as microwave absorption materials (MA) due to the synergistic effect between dielectric and magnetic loss. Herein, the ZnFe2O4/C fibers were fabricated via electrospinning and calcination methods, and then polypyrrole (PPy) successfully coated on the fibers via oxidative polymerization. The ZnFe2O4/C@PPy composites exhibit enhanced EM wave absorption performance with the loading of 25 wt%. The optimal reflection loss (RL) value is up to −66.34 dB (13.80 GHz) and effective absorption bandwidth (EAB) is 5.74 GHz (11.78–17.52 GHz) with a matching thickness of 1.93 mm. Besides, high-efficient absorption performance of the ZnFe2O4/C@PPy composites is mainly attributed to the dielectric loss and ideal impedance matching. This study reveals a novel approach to development of ferrites/carbon fibers coated with PPy, and the ZnFe2O4/C@PPy composites exhibit great potential application as the materials with high-efficient absorption properties.

Electromagnetic wave absorbing materials at high-temperature are urgently needed for stealth aircrafts or aero-engines worked in harsh environments. In this contribution, cobalt-containing siliconboron carbonitride (MOF/SiBCN) nanomaterials were prepared by pyrolyzing metal–organic framework, i.e. cobalt 2-methylimidazole (ZIF-67), and hyperbranched polyborosilazane. The rhombic dodecahedral ZIF-67 and cobalt element promoted in situ formation of dielectric loss phases, including SiC nanocrystals, CoSi nanocrystals and turbostratic carbons. The ZIF-67/SiBCN nanomaterials showed excellent microwave absorption both at room and elevated temperature. The minimum reflection coefficient (RCmin) was −51.6 dB and effective absorption bandwidth (EAB) is 3.93 GHz at room temperature. At an elevated temperature of 600 °C, the RCmin reached −30.29 dB and EAB covered almost the whole X-band (3.95 GHz, 8.45–12.4 GHz). The ZIF-67/SiBCN nanocomposites are promising and useful platform for microwave absorbing materials at high-temperature. It may shed light on the downstream applications in designing next generation areo-engines and stealth aircrafts.

A simple hydrothermal method was used to prepare palladium-doped few-layer molybdenum disulfide nanosheets grown on the surface of a multi-walled carbon nanotube (Pd–MoS2/CNT) with forming a three-dimensional (3D) hierarchical core-shell heterostructure. This paper provides first-hand information on electromagnetic interference (EMI) scattering and electromagnetic (EM) parameters in the X-band (8–12 GHz) microwave frequency range. In this hierarchical core-shell heterostructure, SEM and TEM photos clearly show that CNT forms the core, while Pd-doped few layers MoS2 grown on the surface of CNT is the shell. The Pd-doped MoS2/CNT nanohybrids can greatly improve electrical conductivity, defect dipole polarization, interfacial polarization, dielectric relaxation loss, and mobile charge carriers between core and shell. These are the reason for the substantial enrichment in EMI shielding effectiveness (SE) and dielectric performance. The 10% Pd–MoS2/CNT nanohybrid has a higher EMI SE and dielectric loss tangent (SET ~ 26.50 dB, tan δ e ~2.37) than the 5% Pd–MoS2/CNT (SET ~ 22.50 dB, tan δ e ~1.90) and undoped MoS2/CNT (SET ~ 21.55 dB, tan δ e ~0.92) at the same thickness of 1 mm. The strong EMI SE and dielectric loss tangent are found due to their higher dipole polarization, conduction, and relaxation losses. The doping concentration of Pd-atoms has a significant impact on EM parameters (e′, e″, μ′ & μ″) and EMI scattering parameters (S11, S21, S12 & S22). The experimental results indicated that the 10% Pd–MoS2/CNT nanohybrid might be considered a good EMI shielding and dielectric material for large scale use in intelligence wireless information and communication devices in the future.

The sufficient interface contact in the composite absorbing material is beneficial to increase the dielectric loss and promote the microwave absorption performance. In this paper, the composite nanoparticles (NPs), Fe3O4 covered with ultra-thin carbon layer (Fe3O4/C), were synthesized by simple high temperature solution-phase and subsequent high-temperature steam carbonization methods. Small size Fe3O4/C composite NPs have large heterogeneous interfaces, which can control the polarization loss of composite NPs through the method of interface regulation and achieve high microwave absorption performance. The strongest reflection loss of the composite NPs with an average particle size of 52 nm can reach −58.5 dB at 14.88 GHz with a thickness of 2 mm, and the corresponding effective absorption (RL ≤ -10 dB) bandwidth (EAB) is 5.63 GHz (12.37–18 GHz). In particular, the high-efficiency absorption (RL ≤ -20 dB) bandwidth of Fe3O4/C can reach 15.44 GHz (2–17.44 GHz) with a thickness of 1.7–10 mm. The current method for controlling polarization loss provide a meaningful reference for future microwave absorption research.

Single-component absorbent with wide-band absorption and strong attenuation capability is a challenge for efficient electromagnetic wave absorption. Morphology manipulation is an effective pathway to enhance electromagnetic wave absorption. Herein, naked NiCo2O4 with novel morphology of wood-texture-column-like nanostructure was synthesized for the first time through sodium oxalate-induced hydrothermal synthesis. The electromagnetic parameters are adjusted by controlling the amount of sodium oxalate to optimize absorbing performance. The optimum absorption performance occurs when the molar ratio of sodium oxalate to metal ions is 1.5, in which the effective absorption bandwidth is up to 7.10 GHz (10.90–18 GHz) at only 2.20 mm and the minimum reflection loss is low to −49.78 dB. Notably, the qualified EAB can cover the entire C, X and Ku bands by adjusting the thickness from 1.7 to 5.0 mm. Excellent absorbing performance is attributed to appropriate impedance matching originating from numerous cracks and pores in nanostructures and strong dipole polarization induced dominantly by oxygen vacancy together with lattice distortion. This study provides an excellent candidate for the study of single-component electromagnetic wave absorbents.

In this study, β-SiC is utilized as a novel attenuating agent. A series (5–40 vol%) of β-SiC/AlN microwave attenuating composites with full density are prepared by hot-pressing sintering. The β-SiC incorporation is found to slow AlN grain growth and generate SiC-AlN solid solution during sintering. As the β-SiC content increases to 40 vol%, the conductivity of the composites monotonously increases and demonstrates typical percolation behavior at 17.5 vol%. The microstructure of homogeneously distributed β-SiC and SiC-AlN solid solution endows the composites with enhanced complex permittivity, dielectric loss and absorption capacity. After adjusting the content of β-SiC, the 25 vol% sample shows optimal microwave absorption performance with four absorption peaks at 3.5–5 mm thicknesses. The absorption performance in terms of optimal absorption frequency and thickness is significantly tunable for 25–40 vol%β-SiC samples. This work highlights the great potential of β-SiC/AlN composites as efficient microwave attenuating materials with effectively regulated absorption performance.

Piezoelectric materials are an indispensable part of modern life. Yet the existing environmental issues with conventional lead-based piezoelectrics has motivated scientist to develop novel substitutes including lead-free piezoelectric polymer composites. Following this path, the present research has focused on the fabrication of ternary composites of Polyvinylidene fluoride (PVDF)/Potassium Sodium Niobate (KNN)/nano-Silicon carbide (SiC) via hot compression molding and studying the effect of additives on the PVDF structure and the electrical properties of the composite. The obtained scanning electron micrographs and density measurements showed that the fabrication method provided dense samples. The activated polarization phenomena in the prepared samples enhanced dielectric permittivity and dielectric loss at a constant frequency with increasing KNN and SiC contents. Besides the expected dipole polarization, the presence of interfaces in the composites gave rise to the Maxwell–Wagner–Sillars effect and its corresponding polarization phenomenon. The semiconductive nature of SiC also promoted space charge polarization. However, these properties were frequency-dependent because the first two polarization mechanisms are deactivated at high frequencies. XRD patterns showed that SiC addition can alter the primary crystalline structure of PVDF and promote β-phase formation in the poled samples. Piezoelectric measurements confirmed the significant role of SiC addition to PVDF-KNN composites. The most significant increase in the piezoelectric properties was observed in PVDF-60KNN-1SiC, with a 183% increase in d33 value. The PVDF-80KNN-1SiC had the highest d33 value of 30.5 pC/N. It also had the best piezoelectric voltage coefficient and hence the highest figure of merit. Higher SiC contents restrict the efficiency of poling by forming a conductive path across the sample which would deteriorate the piezoelectric performance of the material. The present findings show that PVDF-KNN-SiC composites can be considered as a potential flexible piezoelectric material for future applications.

As a common flux agent, B2O3–CuO was introduced into Li2TiO3 system to reduce the sintering temperature for the requirements of LTCC applications. The optimal mass ratio of CuO to B2O3 was innovatively explored. When the mass ratio of CuO to B2O3 increased to 1.2:1.0, excellent microwave dielectric properties were obtained in LTMF&LTZN0.892+CB1.2 ceramic of er = 13.23, Q × f = 62,749 GHz, τf = -2.48 ppm/°C and the sintering temperature was reduced from 1300 to 930 °C. In a wide temperature range, the sample still maintain high temperature stability of |τf

Ferroelectric thin films with high tunability, low dielectric loss, high figure-of-merit (FOM) and high thermal stability are attractive to military and civil tunable devices such as phase shifters, filters, etc. In this work, the (100), (110) and (111) highly oriented 0.85Pb(Mg1/3Nb2/3)-0.15PbTiO3 (PMN-15PT) relaxor ferroelectric thin films were prepared by a sol-gel method. The (111) highly oriented PMN-15PT thin film has high dielectric tunability (η) value of ∼ 80% at 1500 kV/cm, high thermal stability (±2% variation) from room temperature to ∼ 450 K and the dielectric tunability is independent from 500 Hz to 10 kHz. The high dielectric tunability of the (111) highly oriented PMN-15PT thin film is associated to the reorientation of polar nanoregions (PNRs) and intrinsic lattice phonon polarization. Meanwhile, the excellent thermal stability may be attributed to the large dielectric diffuseness degree (γ ∼ 1.81) derived from the modified Curie-Weiss law. It is believed that the (111) highly oriented PMN-15PT thin film is an attractive material in the application of the next-generation tunable devices.

Aluminium nitride high-temperature co-fired ceramic (AlN HTCC) substrate is a preferred electronic packaging material. It displays a low thermal expansion coefficient, low dielectric constant, low dielectric loss, and high thermal conductivity at a high frequency. It can also prefabricate the circuit inside. Considering the need to increase the specific surface area of AlN HTCC substrates and thereby enhance the heat dissipation performance, a rapid fabrication method involving chemically assisted laser ablation is proposed to machine microstructures on AlN HTCC substrates. The influence of power, atmosphere, and other factors on the ablation quality of AlN HTCC substrates was explored on this basis. The main component of the ablation products was Al in an Ar atmosphere. However, the modification layers in N2 and O2 atmospheres were composed of multiple components including Al, AlN, and Al2O3. The accuracy of the top and bottom widths of the microgrooves in the Ar atmosphere was higher than those for the N2 and O2 atmospheres. However, the variation of atmosphere had a negligible effect on the ablation depth. When the laser-energy density was 100 J/mm2 and the scanning distance was 10 μm, the ablation depth increased linearly from 150 μm to 350 μm as the laser power increased from 8 W to 20 W. The deviation in laser-energy density was established to predict the surface roughness and optimise the laser parameters. It was observed that the surface roughness increased with an increase in the deviation in laser-energy density. The surface roughness could be reduced by two–three times from that obtained by laser ablation with optimisation.

The combination of multiple loss characteristics is an effective approach to achieve broadband microwave wave absorption performance. The Fe-doped SiOC ceramics were synthesized by polymer derived ceramics (PDCs) method at 1500 °C, and their dielectric and magnetic properties were investigated at 2–18 GHz. The results showed that adding Fe content effectively controlled the composition and content of multiphase products (such as Fe3Si, SiC, SiO2 and turbostratic carbon). Meanwhile, the Fe promoted the change of the grain size. The Fe3Si enhanced the magnetic loss, and the SiC and turbostratic carbon generated by PDCs process significantly increased the polarization and conductance loss. Besides, the magnetic particles Fe3Si and dielectric particles SiO2 improved the impedance matching, which was beneficial to EM wave absorption properties. Impressively, the Fe-doped SiOC ceramics (with Fe addition of 3 wt %) presented the minimum reflection coefficient (RCmin) of −20.5 dB at 10.8 GHz with 2.8 mm. The effective absorption bandwidth (EAB, RC

It is a challenge to reduce the dielectric loss and increase the tunability of pure barium strontium titanate (BST) films for microwave tunable application because these two properties change simultaneously. Herein, a novel composite of strontium titanate (ST) and potassium-doped BST (KBST) has been designed as ST/KBST/ST sandwich-type film with various ST and KBST layers. X-ray diffraction patterns show that the film exhibits cubic perovskite polycrystalline structure composed of BST and ST phase, mainly grow along (110) crystal plane with average grain size of less than 20 nm and decreasing BST phase/ST phase ratio with increasing film thickness. Scanning electron microscope shows that no interfacial layer can be observed, indicating that ST and KBST are fully compounded. Low dielectric loss and high tunability at -10 – 10 V and stable and excellent dielectric properties at 1 GHz are achieved, meeting the needs of microwave tunable application at high frequency. The surface structures are also studied by other analysis methods, and ST/MgBST/ST sandwich-type film is compared.

The high-temperature mechanical and dielectric properties of Si2N2O ceramics are often limited by the introduction of a sintering aid. Herein, dense Si2N2O was prepared at 1700 °C by hot-pressing oxidized amorphous Si3N4 powder without sintering additives. A homogeneous network with short-range order and a SiN3O structure was formed in the oxidized amorphous Si3N4 powder during the hot-pressing process. Si2N2O crystals preferentially nucleated at positions within the SiN3O structure and grew into rod-like and plate-like grains. Fully dense ceramics with mainly crystalline Si2N2O and some residual amorphous phases were obtained. The as-prepared Si2N2O possessed a good flexural strength of 311 ± 14.9 MPa at 1400 °C, oxidation resistance at 1500 °C, and a low dielectric loss tangent of less than 5 × 10−3 at 1000 °C.

Donor-acceptor co-doped rutile TiO2 ceramics with colossal permittivity (CP) have been extensively investigated in recent years due to their potential applications in modern microelectronics. In addition to CP and low dielectric loss, voltage stability is an essential property for CP materials utilized in high-power and high-energy density storage devices. Unfortunately, the voltage stability of CP materials based on co-doped TiO2 does not catch enough attention. Here, we propose a strategy to enhance the voltage stability of co-doped TiO2, where different ionic defect clusters are formed by two acceptor ions with different radii to localize free carriers and result in high performance CP materials. The (Ta + Al + La) co-doped TiO2 ceramic with suitable La/Al ratio exhibits colossal permittivity with excellent temperature stability as well as outstanding dc bias stability. The density functional theory analysis suggests that L a 3 + A l 3 + V O • • T i 3 + defect clusters and Ta5+-Al3+ pairs are responsible for the excellent dielectric properties in (Ta + Al + La) co-doped TiO2. The results and mechanisms presented in this work open up a feasible route to design high performance CP materials via defect engineering.

Ceramic matrix composites are typically prepared by a costly, time-consuming process under severe conditions. Herein, a cost-effective C/SiC composite was fabricated from a silicon gel-derived source by Joule heating. The β-SiC phase was generated via carbothermal reduction, and the carbon fabric showed a well-developed graphitic structure, promoting its thermal and anti-oxidation stabilities. Owing to the excellent dielectric loss in carbon fabric, SiC and SiO2 as well as the micropore structure of the ceramic matrix, the absolute electromagnetic interference shielding (EMI) effectiveness (SSE/t) reached 948.18 dB∙cm2∙g-1 in the X-band, exhibiting an excellent EMI SE. After oxidation at 1000 °C for 10 h in the air, the SSE/t of the composite was only reduced to 846.02 dB∙cm2∙g-1. The C/SiC composite promises the efficient fabrication of high-temperature resistant materials for electromagnetic shielding applications.

With the blossom of information industry, electromagnetic wave technology shows increasingly potential in many fields. Nevertheless, the trouble caused by electromagnetic waves has also drawn extensive attention. For instance, electromagnetic pollution can threaten information safety in vital fields and the normal function of delicate electronic devices. Consequently, electromagnetic pollution and interference become an urgent issue that needs to be addressed. Carbon nanotubes (CNTs) have become a potential candidate to deal with these problems due to many advantages, such as high dielectric loss, remarkable thermodynamic stability, and low density. With the appearance of climbing demands, however, the carbon nanotubes combining various composites have shown greater prospects than the single CNTs in microwave absorbing materials. In this short review, recent advances in CNTs-based microwave absorbing materials were comprehensively discussed. Typically, we introduced the electromagnetic wave absorption mechanism of CNTs-based microwave absorbing materials and generalized the development of CNTs-based microwave absorbers, including CNTs-based magnetic metal composites, CNTs-based ferrite composites, and CNTs-based polymer composites. Ultimately, the growing trend and bottleneck of CNTs-based composites for microwave absorption were analyzed to provide some available ideas to more scientific workers.

Increasing the dielectric loss capacity plays an important role in enhancing the electromagnetic absorption performance of materials. It remains a challenge to simultaneously introduce multiple types of dielectric losses in the material. In this work, we show that the atomic and interfacial dipole polarizations can be simultaneously enhanced by substituting N species into both carbon coating layers and bulk TiC lattices of a core-shell TiC@C material. Additionally, substitution of N species results more exposed TiC(111) facets and refines the TiC grain sizes in the bulk material, which is beneficial for enhancing the scattering of the external electromagnetic waves. The maximum reflection loss of the N substituted TiC@C material is measured as −47.1 dB with an effective absorbing bandwidth of 4.83 GHz at 1.9 mm, which illustrates a valuable way to further tuning the electromagnetic absorption performance of this type of materials.

Polymer-based dielectric composites with enhanced energy storage performances occupy a pivotal position in the modern power electronics industry. Unfortunately, these dielectric composite materials still exist unsolvable problems, especially the deficient breakdown strength (Eb) and heat amassment caused by dielectric loss. Herein, the novel bilayer composite films comprised of pristine poly(vinylidene fluoride) (PVDF) as the top layer and Na0.5Bi0.5TiO3 (NBT)/PVDF composite doped with two-dimensional (2D) NBT platelets as the bottom layer were designed and prepared. Subsequently, the dielectric and energy storage properties of these bilayer structure composite films were analyzed. The results demonstrate that this bilayer structure with optimized NBT content increases the dielectric constant, enhances the Eb, and reduces the dielectric loss, thus notably improving discharged efficiency (η) and discharged energy density (Ue). Eventually, an ultrahigh η of 80.3% and a superior Ue of 22.6 J cm−3 are gained at 650 MV m−1 with the composite layer involving 5 vol% 2D NBT platelets. Therefore, this new strategy of simultaneously increasing the Ue and η of the composite film will provide new thoughts for the exploitation of high-performance capacitors.

In order to fully utilize the advantages that one-dimensional (1D) materials are conducive to form a conductive network and surface wrinkled microspheres can cause multiple reflection. In this paper, two MXene-based magnetic composites have been innovatively fabricated. 1D MXene@Fe3O4 magnetic nanofibers with a diameter of 25 nm are obtained by the self-assembly of single-layer Ti3C2Tx MXene nanosheets and coating Fe3O4 nanoparticles via thermal decomposition method. The micro-scale surface wrinkled porous MXene@Fe3O4 composite microspheres are prepared by simple ultrasonic atomization technology. A high efficiency microwave absorbing system is obtained by blending these two composites. Through the evaluation of microwave absorption performance, the optimal ratio of composite microspheres and nanofibers is conformed to be 7:3. The minimum reflection loss (RLmin) is −63.3 dB at a filler content of 40%. The corresponding matching thickness is 1.8 mm. The maximum effective absorption bandwidth (EABmax) is 5.2 GHz (12.8–18 GHz). Microwave absorbing mechanism study shows that the attenuation approaches include dielectric loss, magnetic loss, multiple reflection and conductive loss from the unique structure and impedance matching.

Barium Strontium Titanate (Ba1-xSrxTiO3, BST) possesses the advantages of high permittivity, low remnant polarization and dielectric loss, suggesting great potential in the application of power capacitors. However, the low maximum polarization severely restricts the achievement of outstanding energy storage properties (ESP). Herein, we design a lead-free bulk ceramic: (1-x)Ba0.55Sr0·45TiO3-xBi0.5Na0.5TiO3 [(1-x)BST-xBNT] (x = 0.1–0.4), prepared by two-step solid-state reaction method. The introduction of BNT contributes to (1) the boost of maximum polarization (from 21 μC/cm2 up to 32.6 μC/cm2) due to Bi3+ lone pair covalent effect (2) strong relaxor behavior (1.71≪ γ 1.84) derived from weakly coupled nanopolar regions, which can be verified by high activation energy Ea = 0.341 eV at x = 0.3, improves the ESP and thermal stability of the ceramics. According to the above strategies, high Wrec = 1.73 J/cm3 and η = 84.4% are achieved in the 0.7BST-0.3BNT ceramics at 206 kV/cm, which is preferable to the previous results regarding BST-based bulk ceramics. The excellent thermal stability (20–120 °C), frequency stability (1–500 Hz), as well as anti-fatigue characteristic (cycling number: 105) were obtained in the 0.7BST-0.3BNT. Furthermore, 0.7BST-0.3BNT ceramics exhibit high-power density (PD = 44.9 MW/cm3) and rapid discharge rate (t0.9 = 99.2 ns) from 20 °C to 120 °C. This work provides a feasible way to achieve good energy storage and charge-discharge properties for pulse power energy storage systems.

A hexagonal boron nitride (h-BN)-bonded porous silicon oxynitride (Si2N2O) composite with a low dielectric constant, low thermal diffusivity, and high thermal shock resistance was fabricated by pressureless sintering, and the phase, microstructure, oxidation resistance, and mechanical and dielectric properties of the composites were investigated. The results demonstrated that Na2CO3 facilitated http://www.youdao.com/w/eng/facilitated/javascript:void(0) ; the generation of Si2N2O. With the subsequent volatilisation of Na2O at high temperatures, near-pure porous Si2N2O ceramics was obtained. However, in the presence of excess Na2CO3 (above 6 wt%), Si2N2O decomposed into Si3N4. The hardness of the Si2N2O/h-BN composite decreased from 1.4 ± 0.15 GPa to 0.4 ± 0.13 GPa with the addition of h-BN, which significantly improved the workability of the material. Moreover, the material exhibited a stable thermal expansion coefficient (3.36 × 10 −6 K−1 at 200 °C and 4.08 × 10 −6 K−1 at 1300 °C), low dielectric constant, and low dielectric loss (e = 3.26, tan δ = 3.21 × 10−3 at a h-BN content of 9 wt%). Thus, it is a potential wave-transparent and thermal insulation material for microwave sintering furnaces.

M-type hexaferrite has attracted much attention for its large magneto-crystalline anisotropic energy, exceptionally good chemical stability, corrosion resistance, high Curie temperature, and high coercivity. In this review paper, our goal is to examine the microwave absorption properties and related studies of M-type hexaferrite-based materials. The microwave absorption properties of hexaferrite-based materials in the S, X, and Ku-band are discussed with their corresponding reflection losses. Complementarity between magnetic loss and dielectric loss is found to have a great impact on the proper absorption of microwaves. The mechanisms corresponding to the microwave absorption in different morphologies and structural adaptations of hexaferrite have been elaborated in the article. The ongoing trends and future perspectives of these materials are also outlined.

The MXene/NiFe2O4 nanocomposites with different MXene (Ti3C2) contents were successfully prepared by one-step hydrothermal method. The crystalline structures, morphologies, magnetic and electromagnetic parameters were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer. With the increase of MXene content, NiFe2O4 (NFO) particles crystallize from the surface to the interlayer for the large specific surface area of MXene, corresponding with the decrease of grain aggregation. The anisotropy was enhanced for the addition of MXene nanosheet, with the maximum saturation magnetization decreasing from 40.50emu/g for NiFe2O4 to 13.18 emu/g for 40%M/NFO (40%wt, M = MXene and NFO NiFe2O4), and the coercivity increasing from 5.12 Oe for NiFe2O4 to 88.29Oe for 40%M/NFO. Compared to NFO, the MXene/NiFe2O4 composite material showed a more significant improvement in the dielectric loss Tangent (tanδe = e''/e′), but had little effects on magnetic loss tangent (tanδμ = μ''/μ′). The microwave absorption performance is improved with the introduction of MXene nanosheets. The minimum reflection loss was -41.2 dB at 13.2 GHz for the 40%M/NFO nanocomposite with a thickness of 2.5 mm.

Dielectric tunable properties in ferroelectric ceramics have been optimized by a variety of approaches, e.g., isovalent/aliovalent substitution, system composite et al., while the study of non-stoichiometric regulation on the performance of BCZT ceramics was rarely concerned. Herein, a series of novel non-stoichiometric (Ba0·91Ca0.09)x (Zr0·18Ti0.82)O3 (BCZTx) ceramic specimens were successfully prepared via solid-state reaction. The microstructures of BCZTx ceramics are simultaneously investigated through XRD and SEM. The diffuse phase transition (DPT) behaviour of BCZTx ceramics are studied by the Lorentz-type empirical formula. The significant enhancement of DPT behaviour is observed at x = 1.03, which probably due to the coaction of the generation of partial Schottky defects and prominent reduction of grain size. Furthermore, a high tunability (k) 87.80%, low dielectric loss (tan δ) 0.141%, and a remarkably enhanced FOM of 623 are achieved in x = 0.99 at a low DC bias electric fields (BEFs) of 7.28 kV/cm and room temperature (RT), which is superior to that of the stoichiometric BCZT ceramics and other available reported BT-based ceramics systems in term of the dielectric tunable properties. Meanwhile, it shows that the temperature dependent CQF value of x = 0.99 remained advantageous around the RT. These findings suggested that non-stoichiometric BCZTx ceramics with x = 0.99 are significantly competitive in the applications of dielectric tunable devices at RT. The non-stoichiometric regulation is an effective approach in improving the dielectric tunability properties of BCZT ceramics.

To substantially prevent electromagnetic threatens, microwave absorbing materials (MAMs) are required to eliminate surplus electromagnetic waves. As a typical MAM, Fe3O4 particles with complex permittivity and permeability have been widely applied due to the coexistence of magnetic loss and dielectric loss. However, the necessary high mass fraction significantly limited its applications, thus Fe3O4 nanostructures have been extensively investigated to overcome this problem. In this work, uniform Fe3O4 nanobelts were prepared by electrospinning and two-step thermal treatment. By controlling the composition and viscosity of the electrospinning precursor solution, Fe3O4 nanobelts with tunable lateral sizes (200 nm–1 μm) were obtained. The samples with low content (only 16.7 wt%) Fe3O4 exhibited wide maximum effective absorbing bandwidths (EAB) over 3 GHz, and Fe3O4 nanobelts with smaller lateral sizes showed a maximum EAB of 4.93 GHz. Meanwhile, Fe3O4 nanobelts with smaller lateral sizes presented superior reflection loss properties, the lowest reflection loss reached −53.93 dB at 10.10 GHz, while the maximum EAB was up to 2.98 GHz. The excellent microwave reflection loss of Fe3O4 nanobelts was contributed to the enhanced synergistic effect of magnetic loss, dielectric loss, and impedance matching, originated from the hierarchically cross-linked networks and shape anisotropies. This study could broaden the practical applications of magnetic absorbers, and provided an approach for the development of shape anisotropic magnetic materials.

Effects of (Li0.5Ga0.5)2+ and (Li0.5Er0.5)2+ doping on the phase structure, electrical, and magnetic properties of 0.75BiFeO3-0.25BaTiO3 (BFO-BT) ceramics were investigated and analyzed. X-ray diffraction measurements suggested a rhombohedral distorted perovskite structure and no structural transformation with the increasing doping content. Rietveld refinement results revealed that (Li0.5Ga0.5)2+ ions were more susceptible to replace the B-sites and (Li0.5Er0.5)2+ ions tended to substitute the A-sites. A significant improvement in the dielectric loss, ferroelectricity, and magnetization was observed for both (Li0.5Ga0.5)2+ and (Li0.5Er0.5)2+-modified BFO–BT ceramics without the addition of MnO2 compared to undoped ceramic samples. Remnant magnetization (Mr) of 0.35 emu/g was reached for LG6. The enhanced magnetic properties were related to the suppressed cycloidal spin structure, the presences of the local lattice disorder and the magnetic impurities induced by the (Li0.5Ga0.5)2+ and (Li0.5Er0.5)2+ substitution.

The development of piezoceramics with high Curie temperature and high piezoelectrical performance has always been a long-cherished goal for many researchers. In this work, we have fabricated 0.55BiFeO3-(0.45-x)PbTiO3-xBa(Zr0.3Ti0.7)O3 ternary ceramics near the morphotropic phase boundary (MPB) by conventional solid-state method. XRD patterns indicate that there is an evolution from the tetragonal (T) to pseudo-cubic (PC) phase with BZT content increasing from 0.125 to 0.225. Also, the slim P-E loop transforms into a saturated shape with the decrease of coercive field Ec. Piezoresponse force microscope (PFM) analysis reveals that when x (BZT content) increases, domain density increases. The optimum piezoelectric coefficient d33 (~220 pC/N) is obtained at x = 0.175, while Curie temperature TC and dielectric loss tanδ are 434 °C and 0.019, respectively. These results show that BF-PT-based piezoceramics are competitive candidates in future high-temperature applications of piezoelectric ceramics.

(1-x)(Bi0.5Na0.5)0.94Ba0.06TiO3-xAgNbO3 lead-free piezoelectric ceramics (abbreviated as BNBT-100xAN) were prepared using the conventional solid-state sintering method. The effects of the introduction of AgNbO3 (AN) dopants for the dielectric and piezoelectric performances of BNBT-100xAN ceramics were systematically studied. The XRD patterns and Raman spectra demonstrated that AN as a modifier was successfully diffused into the BNBT-100xAN lattice and revealed a pseudo-cubic symmetry structure. All samples exhibited a dense surface morphology accompanied by the uniform distribution of elements. A large bipolar strain of ~0.501% and unipolar strain of ~0.481% corresponding to the normalized strain d33* of ~740 p.m./V were achieved for BNBT-1AN ceramic at 65 kV/cm field. The BNBT-4AN ceramic exhibited an excellent temperature-stable permittivity with the range from 59 to 380 °C and its dielectric loss was less than 0.02 between 97 °C and 329 °C. These results revealed that BNBT-100xAN ceramics were more hopeful candidates for actuators, strain sensors, and high-temperature capacitors.

CaCu3-xZnxTi4O12 ceramics (x = 0, 0.05, 0.10) were successfully prepared by a conventional solid-state reaction method. Their structural and dielectric properties, and nonlinear electrical response were systematically inspected. The X-ray diffraction results indicated that single-phase CaCu3Ti4O12 (JCPDS no. 75–2188) was obtained in all sintered ceramics. Changes in the lattice parameter are well-matched with the computational result, indicating an occupation of Zn2+ doping ions at Cu2+ sites. The overall tendency shows that the average grain size decreases when x increases. Due to a decrease in overall grain size, the dielectric permittivity of CaCu3-xZnxTi4O12 decreases expressively. Despite a decrease in the dielectric permittivity, it remains at a high level in the doped ceramics (~3,406–11,441). Besides retention in high dielectric permittivity, the dielectric loss tangent of x = 0.05 and 0.10 (~0.074–0.076) is lower than that of x = 0 (~0.227). A reduction in the dielectric loss tangent in the CaCu3-xZnxTi4O12 ceramics is closely associated with the enhanced grain boundary response. Increases in grain boundary resistance, breakdown electric field, and conduction activation energy of grain boundary as a result of Zn2+ substitution are shown to play a crucial role in improved grain boundary response. Furthermore, the XPS analysis shows the existence of Cu+/Cu2+ and Ti3+/Ti4+, indicating charge compensation due to the loss of oxygen lattice. Based on all results of this work, enhanced dielectric properties of the Zn-doped CCTO can be explained using the internal barrier layer capacitor model.

Nanoparticles with high roughness and complex surface have strong reflection and scattering ability for electromagnetic wave, which can extend the propagation path of electromagnetic wave in absorbing coating, thus exhibiting better microwave absorbing performance. Constructing complex surface has been considered as an effective way to improve the microwave loss ability of microwave absorbers. In this paper, a novel bowknot-like N-doped Co@C magnetic nanoparticle constituted by acicular structural units (BNCoC) has been designed and prepared. Its precursor (BNCoCP) is synthesized by solvothermal method and converted into BNCoC by subsequent vacuum calcination. The main structure of BNCoC is N-doped carbon with Co nanoparticles embedded in it. BNCoC contains dielectric and magnetic components that has both dielectric loss and magnetic loss capabilities. Under the synergistic effect of its unique structure, BNCoC exhibits excellent absorbing performance with a minimum reflection loss of −47.6 dB@11.0 GHz@2.7 mm. Furthermore, the effects of calcination temperature and filler content on microwave absorbing performance are investigated. The electromagnetic parameters are analyzed in depth to reveal the microwave loss mechanism. This work reports a novel high-efficiency microwave absorber with unique structure. It provides a new method for microstructure design of microwave absorbing materials.

Lead-free ferroelectric sol-gel thin films derived from barium strontium titanate (Ba0.85Sr0.15Zr0.1Ti0.9O3, BSZT) were deposited onto two types of electrode: (i) noble metallic Pt- and (ii) conductive oxides LaNiO3- and SrRuO3-coated silicon substrates. The present studies demonstrate that electrode materials impact significantly on morphology, crystallographic orientation, lattice mismatch-induced microstrains and electrical properties of BSZT thin films. Highly (100)-textured BSZT thin films with the highest crystallinity and lowest microstrain were found on conductive oxide electrodes, whereas Pt electrodes showed polycrystalline. Capacitors with oxide LaNiO3 electrode display predominated Schottky emission with a rather low leakage current density ~4.68 × 10−8 A/cm2, while Pt electrode capacitors indicate space-charge limited conduction. Dielectric characterizations in the frequency range of 103–5 × 106 Hz and the dc electric field up to ±800 kV/cm show that the permittivity, loss tangent, and tunability of BSZT films also strongly depend on the electrode materials used. The optimal dielectric tunability with a large figure of merit (FOM ≈ 22.53) and low dielectric loss ( t a n δ ≈ 2.9%), was found to be 66% for BSZT thin films on the conductive LaNiO3 electrode, suggesting that the as-deposited ferroelectric films are promising candidates for applications in tunable microwave elements and related electronic devices.

For extra-high-voltage high-temperature superconducting (HTS) cables, not only high electrical insulation performance but also low dielectric loss is required. Therefore, we focus on a porous synthetic paper with lower dielectric loss, e.g., Tyvek polyethylene nonwoven fabric, than that of polypropylene laminated paper (PPLP), which has been used for a conventional HTS cable insulation system. In this paper, we compare partial discharge inception characteristics for different liquid nitrogen/synthetic paper composite insulation systems. The partial discharge inception electric field strength in the composite insulation system depends on the electric field strength in the porous area of synthetic paper.

The dielectric and structural properties of the as-quenched melts of three CaO–B2O3–SiO2 compositions (denoted CBS-1, CBS-2, and CBS-3) were investigated to determine their suitability for use in millimeter-wave applications. The CBS-1 glass-ceramic exhibited the lowest coefficient of thermal expansion (CTE = 3.2 ppm/°C), lowest dielectric constant (er = 4.04) at 60 GHz, and highest dielectric loss (tan δ = 0.0029) at 60 GHz, which were attributed to the presence of quartz (SiO2) as the major phase. In contrast, as the major phase constituent of the CBS-2 and CBS-3 glass-ceramics was β-CaSiO3, they presented relatively high CTEs (6.6 and 5.9 ppm/°C, respectively), relatively high dielectric constants at 60 GHz (6.29 and 7.61, respectively), and relatively low dielectric losses at 60 GHz (0.0020 and 0.0012, respectively). The CBS-1 glass-ceramic exhibited the highest dielectric loss because of the presence of SiO2 as the major phase constituent as well as lattice scattering induced by the high glassy phase content. The thermal conductivities (κ) of the CBS-1, CBS-2, and CBS-3 glass-ceramics were determined to be 2.43, 1.06, and 0.82 W/mK, respectively. Structural analysis using Raman and Fourier transform infrared spectroscopy revealed an absence of nonbridging oxygen in the CBS-1 glass-ceramic, while the high CaO content (>40 mol%) of the CBS-2 and CBS-3 glass-ceramics triggered the formation of nonbridging oxygen in the tetrahedral silicate units. The increase in CaO content of the glass-ceramics increased the number of nonbridging oxygen atoms, thereby resulting in the relaxation of the structure. Consequently, the CBS-2 and CBS-3 glass-ceramics exhibited low thermal conductivity. All the prepared glass-ceramics presented high electrical resistivities of greater than 5 × 1011 Ω cm. The CBS-1 glass-ceramic displayed the highest breakdown strength of 15.20 kV/mm. Overall, the excellent microwave dielectric properties and thermal properties of the CBS glass-ceramics will facilitate the utilization of these materials in millimeter-wave applications.

Covalent bond usually ensures a stable connection between nonmetallic atoms. However, the traditional reflux method usually requires the construction of complex instruments and equipment with tedious steps to ensure airtightness and reaction stability. In this work, an advanced method is adopted to bind core–shell CoFe2O4@PPy and rGO tightly via the aid of 2-(1H-pyrrol-1-yl)ethanamine (PyEA), dispense with a high-temperature environment or protective gas. Cobalt ferrite core and polypyrrole shell collaborate to approach suitable magnetic and conduction loss, while reduced graphene oxide usually provides a stable sheet structure for interface multiple reflections, and replenish the insufficient dielectric loss. The filled biscuit-shaped covalently bond CoFe2O4@PPy-rGO has a fantastically broad absorption bandwidth of 13.12 GHz under the thickness of 3.6 mm, together with a minimum reflection loss of −50.1 dB at 6.56 GHz, achieving both impedance matching and attenuation matching, and effectively responding to all electromagnetic waves in the X and Ku bands. Thus, the covalently bonded CoFe2O4@PPy-rGO has potential application in broadband absorption.

Ho-substituted Li–Ni ferrites with composition L i1.2Ni0.4HoxFe2-xO4; 0≤ x ≤ 0.15 were synthesized by a self-ignited sol-gel process. An annealing temperature of 950 °C is estimated via thermal-gravimetric (TGA) analysis. X-ray diffraction (XRD) scans have confirmed the formation of the ferrite phase with a spinel structure in all samples. Substitution of Ho ions on the B-site significantly reduced the porosity from 38 -to 23% and the crystallite size from 23.4 -to 21.7 nm. Microstructural analysis revealed a denser structure with an increase in Ho content. Dielectric results showed that both the dielectric loss and dielectric constant depict a nonlinear variation with the addition of Ho. Complex impedance behavior with a single semicircle for all samples suggests the predominant effect of the grain boundary mechanism. The substitution of Ho ions in place of Fe ions significantly decreased the electrical conductivity. The anisotropic Ho3+ ions reinforce the L-S coupling which consequently enhanced the coercive force from 145 -to 389 Oe, and thus the anisotropy constant.

Ni2+ modified MgTa2O6 ceramics with a trirutile phase and space group P42/mnm were obtained. The correlations between crystallographic characteristics and microwave dielectric performance of MgTa2O6 ceramics were systematically studied based on the chemistry bond theory (PVL theory) for the first time. The results indicate that the introduction of Ni2+ causes a change in polarizability and the Mg–O bond ionicity, which contributes to the variation of dielectric constant. Moreover, the lattice energy, and packing fraction, full width at half maximum of the Raman peak of Ta–O bond, as the quantitative characterization of crystallographic parameters, regulate the dielectric loss of MgTa2O6 ceramics in GHz frequency band. In addition, the study of sintering behavior shows that the densification and micromorphology are the crucial factors affecting the microwave dielectric performance. Typically, Ni2+ doping on the A-site of MgTa2O6 can effectively promote the Q × f values to 173,000 GHz (at 7.43 GHz), which ensures its applicability in 5G communication technology.

(1−x)K0.5Na0.5NbO3−xBi(Zn2/3Nb1/3)O3 ((1−x)KNN−xBZN, x = 0.010, 0.015, 0.020, 0.025, and 0.030) lead-free ceramics were fabricated via a traditional solid-state method. The crystal structure, microstructure, dielectric, and conductivity behavior of this system were studied. Combined with X-ray diffraction (XRD) patterns, Rietveld refinement, and dielectric spectroscopy, an orthorhombic phase was determined for x = 0.010, an orthorhombic-tetragonal mixed phase was identified for x = 0.015, and a rhombohedral symmetry appears in 0.020 ⩽ x ⩽ 0.030. Both 0.98KNN−0.02BZN and 0.975KNN−0.025BZN ceramics exhibit stable permittivity and low dielectric loss tangent (tanδ) in wide temperature ranges owing to the combination of rhombohedral-tetragonal step-like feature and the diffuse phase transition from tetragonal to cubic. The activation energies of dielectric relaxation and conductivity behavior at high temperatures initially decrease slightly, then drop sharply, and finally decline slowly, which could be attributed to microstructure morphologies and the concentration of oxygen vacancies.

A ternary solid-solution piezoelectric ceramic of rare-earth oxides modified 0.03 Pb(Mn1/3Sb2/3)O3-0.97 Pb(Zr0.505Ti0.495)O3 + x wt.% CuO + y wt.% Bi2O3 (PMS-PZT + x wt.% CuO + y wt. % Bi2O3) (x, y = 0–0.2) was successfully prepared via a transient-liquid-phase sintering. Both Cu2+ and Bi3+ were believed to replace the A-site Pb ions and to evidently induce the lattice shrinkage and the distortion decrease. However, the addition of only a small amount of CuO was found to effectively reduce the sintering temperature, sustain good piezoelectric properties and predominant transgranular fracture modes, but obviously increase the average grain size and high-field dielectric loss. Further experimental results indicate that the grain growth of the ceramics was inhibited effectively and the high-field dielectric loss was reduced through CuO and Bi2O3 co-doping. The 0.05 wt% CuO and 0.15 wt% Bi2O3 co-doped PMS-PZT ceramics sintered at 1050 °C exhibit excellent dielectric and piezoelectric properties of d33 = 410 pC/N, kp = 0.62, Qm = 1478, er = 1550, tan δ = 0.8% (400 V/mm) and Tc = 330 °C. The experimental results can provide a solid fundament for multilayer piezoelectric actuating devices.

Recycling valuable metal elements from metallurgical slags and exploring their functional material applications have attracted more recent attention. In this paper, Fe3O4 particles with unique structures, solid solutions of Mg, Ni, and Co and inlays of silicates in magnetite crystals were extracted from nickel slag by molten oxidation and magnetic separation processes. The microstructure, morphology, magnetic and electromagnetic properties, and microwave absorption performance of the Fe3O4 particles were characterized. The results show that the Fe3O4 crystals oxidized at 1400 °C exhibit granular shapes with a uniform distribution in the silicate matrix, while they change into both dendritic and granular morphology at 1450 °C and finally into dendritic structures at 1500 °C. The Fe3O4 particles prepared at 1400 °C reach an optimal reflection loss value of −29.90 dB under a thickness of 3.5 mm and an effective absorbing frequency band of 3.28 GHz (5.52–8.80 GHz), indicating that their unique structure favours microwave absorption. The joint action of strong magnetic loss and the appropriate dielectric loss were supposed to sustain the absorption mechanism of the Fe3O4 particles.

In this work, the Co2+-Ti4+ co-doped hexagonal barium ferrite Ba(CoTi)xFe12-2xO19 (x = 1.0, 1.2, 1.4, abbreviated as BFCTO-x) nanoparticles were synthesized by sol-gel method. The XRD and SEM confirm that the BFCTO-x nanoparticles are of high quality of single hexagonal system with sheet nanostructure and average grain size about 200 nm. With the increase in x from 1.0 to 1.4, the magnetic properties Hc and Mr of nanoparticles decreased rapidly suggest that Co2+-Ti4+ co-doped induced more vacancy defects. Relying on the synergistic effects from dielectric loss and magnetic loss, as well as the abundant interface and ion substitution defects of nanoscale particles, the samples show an excellent microwave absorption performance at the lower frequency (

(1-x)[0.94(Bi0.5Na0.5)TiO3-0.06BaTiO3]-xBa(Sn0.70Nb0.24)O3 (abbreviated as BNTBT-100xBSN) lead-free ceramics were fabricated with a relative density greater than 96 %, and the structure as well as performance were tested. BNTBT-100xBSN ceramics are pseudo-cubic perovskite structure, with dense surface morphology. Doping BSN can effectively reduce the dielectric loss of ceramics and increase the relaxation properties to a certain extent. The randomly distributed ferroelectric phase was replaced by polar nano regions, thereby improving the electro-strain and energy storage performance of the system. The largest electro-strain and the corresponding normalized strain (d33*) reach ~ 0.43 % and 633 pm/V respectively in the BNTBT-1BSN ceramic. The largest effective energy storage density reaching ~ 1.28 J/cm3 was tested in BNTBT-2BSN. BNTBT-100xBSN ceramics provide a feasible idea for the systematic research of lead-free ferroelectrics and improvements in electro-strain and energy storage applications.

The effects of Cd2+ ions on the microstructure, magnetic properties, and dielectric properties of Bi2O3-added MgFe2O4 ferrites (CdxMg1-xFe2O4, x = 0.00, 0.15, 0.30 and 0.45) are obtained by adopting the solid-state reaction method at a low temperature (910 °C). The objective is to achieve matching impedances, low magnetic and dielectric losses (tan δμ and tan δe, respectively), and a relatively large miniaturization factor to reduce antenna size. Experimental results indicate that the cations occupying the tetrahedral (A) and octahedral (B) ion sites are redistributed, resulting in an enhanced super-exchange interaction between the two sublattices. As a result, improved magnetization, including the increase in saturation magnetization (41.74 emu/g) and decrease in coercivity (63.75 Oe), is realized. The real part of permeability (µ′) also increases with increasing concentration of Cd2+ ions. When x is 0.15, matching impedances with equivalent μ′ and e′ values are obtained over a long frequency range (1–150 MHz). Moreover, the formation of a dense microstructure guarantees that losses occur at low orders of magnitude (tan δμ ≈ 10−2 and tan δe ≈ 10−3). Accordingly, these properties afford wide application perspectives for the proposed compounds in the high-frequency region, i.e., from high-frequency to very-high-frequency bands.

Dielectric capacitors with large energy storage density, low hysteresis loss, low temperature dependence and high temperature adaptability show great advantages in high temperature applications of electronic devices. In this work, a large energy storage density (W ~ 28.776 J/cm3) and ultra-high efficiency (η ~ 87.36%) have been simultaneously achieved in the CuX(Ba0.88Ca0.12)1-X(Zr0.12Ti0.88)O3 (X = 0.1) lead-free relaxor ferroelectric thin film capacitors deposited on Pt(111)/TiOX/SiO2/Si(100) substrates by using a sol-gel method. The results show that the dielectric permittivity and dielectric loss change a little in the temperature range of 30–400 °C. The reason of low dielectric loss and temperature insensitivity is revealed by means of Raman spectrum fitting and equivalent circuit model (the I-E curve of ferroelectric materials is regarded as an equivalent circuit of equivalent capacitance (C), equivalent resistance (R) and polarization charge (Ip(t)) in parallel, given by the equation I ( t ) = V ( t ) / R + K C + I p ( t ) ). The results prove that the stability of slope (K) is positively correlated with the stability of energy storage performance of ferroelectric materials, which provides the basis for the evaluation of energy storage performance of ferroelectric materials.