Nb2O5-doped NiZnCo ferrite ceramics with ultra-high magnetic quality factor and low coercivity for high-frequency electronic devices

This work investigates the influence of niobium pentoxide (Nb₂O₅) as dopant, on the structural, magnetic, and dielectric properties of NiZnCo ferrites. The results showed that Nb₂O₅ was an effective dopant, and the Nb⁵⁺ ions entered the B site to replace Fe³⁺ ions, which altered the electromagnetic properties of the NiZnCo ferrite. In particular, the coercivity (H_c) was 20～24 Oe, and the magnetic quality factor (Q), was more than 200 at x = 0 and x = 0.1 wt%, which is 4～5 times higher than that of NiZn and NiCuZn ferrites. Excellent electromagnetic properties were obtained for 0.1 wt% Nb₂O₅-doped NiZnCo ferrite, i.e., M_s = 88.3 emu/g, H_c =20.4 Oe, ρ = 2.4 × 10⁵ Ω m and Q = 202 @20 MHz. These excellent electromagnetic properties of Nb₂O₅-doped NiZnCo ferrites could be potentially applied to resonators and capacitors at high frequency.     

Structural,magnetic and electrical properties of K0.5Na0.5NbO3 doped NiZnCo ferrite for high frequency device

Ni_0.6Zn_0.4Co_0.2Fe_1.8O₄ ferrites doped with x wt.% K_0.5Na_0.5NbO₃ (0.00≤x≤1.00) were successfully prepared by solid-state reaction method. The lattice parameters a decreased and the diffraction peak of (311) shifted to higher angle with the increase of K_0.5Na_0.5NbO₃ (KNN) content. The grain size D initially increased to 3.12 μm (x = 0.50) and then reduced to 2.66 μm (x=1.00). The study also showed the addition of KNN effectively improved magnetic and electrical properties of NiZnCo ferrites. The saturation magnetization Ms decreased from 60.59 to 46.11 emu/g and the coercivity Hc overall showed a decreasing trend from 84.64–67.00 Oe. The dielectric constant ε´ of prepared samples increased when x≤0.75, then decreased when x>0.75, and all prepared samples had low loss tangent tanδ at high frequency. In addition, all samples exhibited high resistivity ρ and activation energy E_ρ.     

Low loss and tailored high-frequency performances of BaO-doped NiZnCo magneto-dielectric ferrites

Spinel ferrite ceramics of nominal composition Ni_0.5Zn_0.3Co_0.2Fe₂O₄ (NiZnCo) with various BaO doping were successfully synthesized for applications as novel high-frequency magneto-dielectric materials. The influences of BaO doping on the crystal phase, density, microstructure, and magnetic and dielectric performances in the frequency range of 0.1 to 5 GHz were systematically studied. It is revealed that the doped Ba²⁺ ions aggregate to the grain-boundary regions and lead to the formation of BaFe₂O₄ phase that significantly restrains the growth of NiZnCo ferrite grains. Correspondingly, permeability and permittivity are effectively tailored through the varied grain size and density, which is demonstrated by the magnetic circuit model and the modified effective medium theory proposed herein. As BaO content x = 1.2-1.8 mol%, the NiZnCo ferrites reveal the excellent performance with almost equal values of μ′ and ε′, yielding a characteristic impedance to be nearly identical as that of free space over a wide frequency range of the VHF and UHF bands. Furthermore, the magnetic loss is effectively reduced at high frequencies, where the typical tan δ_μ at 0.5 GHz is decreased to ~0.043 with a reduction of up to 37% and the loss factor (tan δ_μ/μ′) is as low as ~0.006.     

Cd-substituted Mg composites with dual-equivalent permeability and permittivity for high-frequency miniaturization antennas

Spinel Mg ferrites Mg_1-xCd_xCo_0.05Fe_1.95O₄ (x=0.0, 0.2, 0.3 and 0.4) as potential agents for the miniaturization of high frequency antennas are presented. All the synthesized compositions were experimentally revealed to possess pure spinel phase. Dual-equivalent permeability and permittivity (μ'≈26, ε'≈25, x=0.3 and μ'≈29, ε'≈28, x=0.4) from 5 to 100 MHz can be achieved by introducing Cd²⁺ ions, yielding large miniaturization factors of up to 25 and 28. To figure out the effects of Cd²⁺ ions substitution on magnetic and dielectric properties, the change in microstructure is mainly investigated. Meanwhile, enhanced magnetic properties including upward saturation magnetization (Ms) (approximately 47.60 emu/g) and reduced coercivity (approximately 54.22 Oe) are obtained due to increased grain size and denser microstructure arrangements reflected from scanning electron microscopy images. With low magnitude order of magnetic and dielectric losses factors (tanδ_ε reaches 10^-4, tanδ_μ reaches 10^-2), the composites can potentially exhibit high operating efficiencies at high frequencies.     

Silacyclobutane-functionalized cyclosiloxanes as photoactive precursors for high thermal stability,low dielectric constant and low dielectric loss polymers

Low dielectric photoactive materials have significant potential as components in future microelectronics. Although a number of photosensitive groups have been used to construct photopatternable materials, it remains challenging to introduce these groups into polymer chains via facile yet controlled polymerization techniques. The present work demonstrates the synthesis of a new class of photoactive cyclosiloxane monomers having hybrid siloxane-carbosilane main chains. These compounds can be cured by applying ultraviolet radiation and heat to promote the reaction of the silacyclobutene units and form hyper-cross-linked cyclosiloxanes. The cured resins show high thermal stability (with T_5% values in the range of 460–550°C), low dielectric constants (2.36–2.76 at 10 MHz) and low dielectric losses (10⁻³ at 10 MHz). Thus, these polymers could possibly be used as high-performance dielectric materials.     

Synthesis of a low-firing BaSi2O5 microwave dielectric ceramics with low dielectric constant

In this study, BaSi₂O₅ ceramics with an orthorhombic structure were synthesized by using a traditional solid-state method at a low temperature by doping with Li₂O–B₂O₃–CaO–CuO (LBCC) glass. The phase composition, mechanism of low-temperature sintering, microwave dielectric properties, and changes in the mesophase during the heating of low-temperature sintered BaSi₂O₅ ceramics were examined by performing an X-ray diffraction analysis. A compact matrix of BaSi₂O₅ can be wetted by the liquid phase of the formed LBCC glass. Therefore, LBCC glass with different doping percentages can effectively reduce the sintering temperature of BaSi₂O₅. The microwave dielectric properties of BaSi₂O₅ ceramics sintered at 900 °C at 4 wt% of LBCC glass were determined: ε_r = 7.32, Q × f = 19,002 GHz, and τ_f = ?35.8 ppm/°C. The chemical compatibility of the samples with Ag was studied at 4 wt% doping with LBCC glass, and the samples were fired for 4 h at 900 °C.     

Fumed SiO2 nanoparticle reinforced biopolymer blend nanocomposites with high dielectric constant and low dielectric loss for flexible organic electronics

In the present study, fumed silica (SiO₂) nanoparticle reinforced poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) blend nanocomposite films were prepared via a simple solution‐blending technique. Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to elucidate the successful incorporation of SiO₂ nanoparticles in the PVA/PVP blend matrix. A thermogravimetric analyzer was used to evaluate the thermal stability of the nanocomposites. The dielectric properties such as dielectric constant (?) and dielectric loss (tan δ) of the PVA/PVP/SiO₂ nanocomposite films were evaluated in the broadband frequency range of 10^?2 Hz to 20 MHz and for temperatures in the range 40–150 °C. The FTIR and UV–vis spectroscopy results implied the presence of hydrogen bonding interaction between SiO₂ and the PVA/PVP blend matrix. The XRD and SEM results revealed that SiO₂ nanoparticles were uniformly dispersed in the PVA/PVP blend matrix. The dielectric property analysis revealed that the dielectric constant values of the nanocomposites are higher than those of PVA/PVP blends. The maximum dielectric constant and the dielectric loss were 125 (10^?2 Hz, 150 °C) and 1.1 (10^?2 Hz, 70 °C), respectively, for PVA/PVP/SiO₂ nanocomposites with 25 wt % SiO₂ content. These results enable the preparation of dielectric nanocomposites using a facile solution‐casting method that exhibit the desirable dielectric performance for flexible organic electronics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44427.     

Novel positive‐type photosensitive polyimide with low dielectric constant

A novel positive‐type photosensitive polyimide (PSPI) with a low dielectric constant was developed. The PSPI system was composed of soluble block PI (Bco‐PI) with a hydroxy group and diazonaphthoquinone as a photoreactive compound. The base Bco‐PI was prepared by a direct one‐pot polycondensation of 2,2‐bis(3‐amino‐4‐hydroxy‐phenylhexafluoropropane), 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, and cyclohexanetetracarboxylic dianhydride in the presence of a γ‐valerolactone and pyridine catalyst system using N‐methyl‐2‐pyrrolidone as the solvent. The film of Bco‐PI was colorless and transparent, both important factors for a PSPI. Photosensitive soluble block PI (Bco‐PI), containing 20 wt % ester of 2,3,4‐trihydroxybenzophenone with 1,2‐naphthoquinone‐(2)‐diazide‐5‐sulfonic acid (NT200), showed a sensitivity of 350 mJ/cm² and a contrast of 1.20 when it was exposed to UV light, followed by development with 5% tetramethylammonium hydroxide aqueous solution at room temperature. The estimated optical dielectric constants of the PIs with and without NT200 were 2.68 and 2.75, respectively. These values were significantly lower than those of conventional aromatic PIs, such as Kapton film (50EN). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 15–21, 2005     

Dielectric properties of high coercivity barium ferrite–natural rubber composites

The effect of frequency, temperature, and BaFe₁₂O₁₉ (BF) content on the dielectric constant $ \acute\varepsilon $ , dielectric loss ε″, and tan δ were studied for barium ferrite—natural rubber composites (RFC). The dielectric constant for barium ferrite was related to the preparation method, meanwhile the dielectric constant of natural rubber (NR) is relatively large compared to the theoretical value. The results showed that $ \acute\varepsilon $ , ε″, and tan δ for RFC decrease as the frequency increases, however, at higher frequencies, the effect significantly weakens. At low ferrite loading, the dielectric properties are strongly influenced by BF content. Strong correlation between magnetic initial permeability and dielectric constant for hard magnetic material polymer composites was also observed. Increasing the content of barium ferrite in NR matrix enhances both ε″ and tan δ. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Epoxy/benzoxazinyl POSS nanocomposite resin with low dielectric constant and excellent thermal stability

Benzoxazinyl modified polyhedral oligomeric silsesquioxane (BZPOSS) is successfully synthesized and used to prepare nanocomposites with bisphenol A type epoxy resin (E51). The differential scanning calorimetry results showed the curing peak temperature of E51/BZPOSS blend decrease to 242°C, suggesting the high catalytic activity of BZPOSS to the polymerization of E51. The scanning electron microscope micrographs of poly(E51/BZPOSS)s and silicon element distribution maps given by EDS both demonstrated homogeneous dispersion of BZPOSS. Dielectric properties tests confirmed the dielectric constant can be reduced by the introduction of BZPOSS, which is attributed to the nano-pores from the cage structure of POSS. When 20 wt% BZPOSS was added, the dielectric constant decreased to 2.28 at 1 MHz. Meanwhile, DMA and TGA results indicated the thermal stability and heat resistance of poly(E51/BZPOSS)s at high temperature increased with the increase of BZPOSS, which is due to the increase of the crosslinking density and the change of crosslinking structure of copolymer.     

Polyimide hollow glass microspheres composite films with low dielectric constant and excellent thermal performance

Nowadays, polyimide (PI) with low dielectric constant is expected to be widely applied in microelectronics. For this reason, hollow glass microspheres (HGM) modified by silane coupling agent KH-550 (K-HGM), a series of HGM/PI and K-HGM/PI composite films with excellent thermal performance, hydrophobic and low dielectric constant were fabricated by in situ polymerization. The effect of HGM/K-HGM content on the properties of composite films was studied. The superior heat resistance of HGM can improve the thermal performance of composite films. Due to silane coupling agent KH-550, K-HGM exhibits a good interfacial compatibility with PI matrix and forms an interfacial adhesion region. With the HGM loading of 6%, comparing with pure PI films, the glass transition temperatures (T_g) of composite films were dramatically increased by 32.3°C. Especially, the low dielectric constant of 2.21 and dielectric loss of 0.0059 at 1 MHz were obtained for the PI/K-HGM composite film with addition of 8 wt%. Thus, PI/K-HGM composite films show more excellent performance. The current work provides a promising solution for fabrication of PI with low dielectric constant and superior thermal performance that may be applied in microelectronics industry.     

New copper phthalocyanine oligomers for high dielectric constant polymer films

We report here the synthesis of two new oligomeric copper phthalocyanine (CuPc) derivatives by esterification of the corresponding carboxylic acids with tri(ethylene glycol) monomethyl ether. The solubility of these derivatives in N,N′‐dimethylformamide (DMF) enabled us to perform dielectric studies with poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐TrFE), acting as the host polymer matrix. The highest room temperature dielectric constant achieved is 94 at 100 Hz, compared with 12 for the base polymer host matrix. Thermogravimetric analyzes of the polymer films showed that they are thermostable at 100°C for a long period of time. Scanning electron microscopy (SEM) images of the films have also been analyzed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

EPDM—陶瓷高介电常数低损耗复合电介质薄膜

采用三元乙丙橡胶（ＥＰＤＭ） 与高介电常数陶瓷粉复合制备高介电常数低损耗复合电介质薄膜,解决聚丙烯—陶瓷复合电介质膜发脆问题。对ＥＰＤＭ 和不同陶瓷粉体的复合进行了较系统的研究,对影响复合电介质薄膜性能的因素、复合工艺条件等作了探讨。在保持复合薄膜柔软的条件下,介电常数达３０,比ＥＰＤＭ 大幅度提高且损耗很小,容量温度变化率小于５％ （－２５℃～８５℃）。体积电阻率１０１５Ωｃｍ ,击穿强度大于５０ｋＶ／ｍｍ 。     

High permittivity and low dielectric loss of the (Ca0.9Sr0.1)1-xLa2x/3Cu3Ti4O12 ceramics

In this work, we have systematically studied the effects of La³⁺/Sr²⁺ dopants on the crystal structure, microstructure, dielectric response and electrical properties of (Ca_0.9Sr_0.1)_1-xLa_2x/3Cu₃Ti₄O₁₂ (x = 0, 0.025, 0.05 and 0.075) ceramics. XRD results show that the lattice parameter increases with the increase in the La³⁺ content. SEM micrographs illustrate that a small amount added of La³⁺ can reduce the grain size of CCTO during sintering. With increasing La³⁺ content, the grains grow larger. Dielectric measurements indicated that all doped samples synthesized by the solid-state reaction exhibit giant dielectric constants ε'>10⁴ over a large frequency range (10 Hz to 1 MHz) and at any temperature below 600 K. In particular, the ceramic with x = 0.05 exhibits a colossal dielectric permittivity ～5.49 × 10⁴; which increases by about 50% compared to that of the undoped ceramic. In addition, the doped ceramic also presents a low dielectric loss ～ 0.08 at 20 °C and 0.6 kHz. The giant dielectric properties of these samples can be explained by the (IBLC) model.     

A novel BaMg1.98Zn0.02V2O8 ceramic with low dielectric loss and good temperature stability for low temperature co-fired ceramic technology

In this paper, a series of BaMg_2-xZn_xV₂O₈ (0.02 ≤ x ≤ 0.08) ceramic has been obtained by ionic substitution at the Mg-site of BaMg₂V₂O₈ ceramics through the conventional solid-state reaction method. The relationship between the surface morphology and the microwave properties of ceramic samples was analyzed intensively. The results showed that the substitution of Mg²⁺ by an appropriate amount of Zn²⁺ can promote their densification, lower their sintering temperature, and reduce the dielectric loss of BaMg₂V₂O₈ ceramics significantly. The BaMg_1.98Zn_0.02V₂O₈ ceramic exhibits microwave dielectric properties as ε_r ～13.4, Q × f ～ 178,760 GHz, τ_f ～ -14.9 ppm/°C at the optimum sintering temperature (940 °C). This indicates that the ceramic prepared in this work, which combines low dielectric loss, good temperature stability, and low-temperature sintering ability, can be an ideal microwave dielectric material for low-temperature co-firing technology.     

Three-phase borate solid solution with low sintering temperature,high-quality factor,and low dielectric constant

The sintering and microwave dielectric properties of a ceramic material based on the mixing of Mg₃B₂O₆ and Zn₃B₂O₆ have been widely studied using first-principles calculations and experimental solid-state reactions. Characterization methods include the Network Analyzer, X-ray, Raman diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and differential-thermal and thermo-mechanical analyzer. The increasing amount of Mg²⁺ results in the appearance of Mg₂B₂O₅ and ZnO, and the mutual substitution (Mg²⁺ and Zn²⁺) phenomenon has emerged in Zn₃B₂O₆ and Mg₂B₂O₅. The mechanisms have been explained with the help of DFT calculations. The bond parameters and electron distributions of the ZnO₄ tetrahedron and MgO₆ octahedron have been modified due to substitution. The sintering, substitution, and phase formation properties have been analyzed quantitatively through the energy parameters. The best dielectric properties were obtained for x = 0.20 sintered at 950°C, ε_r = 6.47, Q × f = 89 600 GHz (15.2 GHz), τ_f = −48.6 ppm/°C, relative density = 96.7%. The mixing of Zn₃B₂O₆ and Mg₃B₂O₆ ceramics is a feasible method to obtain a ceramic with low sintering temperature and excellent dielectric properties.     

Review of polymer materials with low dielectric constant

One of the exciting and promising developments in material science today is the design and synthesis of novel low‐dielectric‐constant polymer materials, which are found to have potential applications in the field of ultralarge‐scale integration, capacitors and other electronic circuits as insulating and/or dielectric materials. In this article the new polymer dielectric materials reported in recent years are reviewed, including aromatic (heteroaromatic) polymers, silicon‐containing polymers, fluorinated polymers, porous polymers, etc. In summarizing the review, the development, potential applications and future directions of polymer materials with low dielectric constant are discussed. Copyright © 2010 Society of Chemical Industry     

Synthesis of CaAl2xB2O4+3x: Novel microwave dielectric ceramics with low permittivity and low loss

Novel CaAl_2xB₂O_4+3x (x = 0.25, 0.5, 0.75, and 1) ceramics were prepared via solid-state reaction method. The investigation is concentrated on sintering behavior, phase composition and dielectric properties of CaAl_2xB₂O_4+3x ceramics with various ratios of Al₂O₃ content. The optimal sintering temperature and the content of CaAl₂B₂O₇ are highly related to the variation of x value. CaAl_2xB₂O_4+3x ceramics possess excellent microwave dielectric properties: ε_r = 5.8 ± 0.05, Q × f = 63,338 ± 2690 GHz (@13.57 GHz), and τ_f=-29 ± 2 ppm/℃ when sintered at 940 ℃ for x = 0.5. Comparing the properties of CaAl_2xB₂O_4+3x ceramics with reported borate ceramics, the ceramics prepared in this study with low dielectric loss and low sintering temperature have promising prospects in LTCC technology.     

Two-step sintering of M-type strontium ferrite with high coercivity

Two-step sintering (TSS) was applied on the M-type Sr-hexaferrite to control grain growth and form a desirable microstructure during the final stage of sintering. The process involved T₁ (temperature in the first sintering stage), t₁ (holding time at T₁), T₂ (temperature in the second sintering stage), and t₂ (holding time at T₂). The effects of each setting parameter on the density, grain growth, degree of orientation and magnetic properties were systematically investigated. The results revealed that T₁ was the main factor that primarily controlled microstructure and magnetic properties. Compared with conventional sintering (CS) process, the magnets with smaller average grain size were achieved by TSS, which suggested that two-step sintering could improve the coercivity of Sr-hexaferrites. It was shown that the high integrated magnetic properties for Sr-hexaferrites, including B_r =?440.4 mT, H_cj =?328.2?kA/m and (BH)_max =?37.6?kJ/m³, were obtained under the optimum processing condition: T₁ =?1200?°C, T₂ =?1000?°C, t₁ =?5?min, and t₂ =?2?h.     

High-performance PA1/TPU films with enhanced dielectric constant and low loss tangent

Polymer composites with high dielectric constant are promising materials for energy-storage application. However, their development has generally been hindered due to the challenge to balance dielectric constant and loss tangent. In this work, a novel thermoplastic polyurethane (TPU)-based composite with high dielectric constant and low loss tangent was prepared by inducing polyamide-1(PA1). The optimal content of PA1 in TPU matrix was 1.0 wt %. Importantly, the dielectric constant of TPU exhibited great stability at the frequency range of 10³–10⁶ Hz and increased sharply with the addition of PA1. In specific, the dielectric constant of TPU increased from 8 to 41 with the incorporation of 1.0 wt % PA1, which was five times higher than that of pure TPU. Meanwhile, the loss tangent still kept at a low level of less than 0.02. This work may provide a new direction for preparation of dielectric polymer composites with excellent comprehensive performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48469.