Ferrite ceramic filled poly-dimethylsiloxane composite with enhanced magnetic-dielectric properties as substrate material for flexible electronics

Improving magnetic-dielectric properties of polymer materials, through filler of functional ceramics, provides feasibility to develop high-frequency flexible electronics. Poly-dimethylsiloxane (PDMS), an inert silicone with low elasticity modulus and high transparency, has been considered a promising candidate for flexible electronics. Current PDMS matrix used in high-frequency devices suffers from unsatisfactory properties due to very low dielectric constant. In this study, using ultrasonic stirring and vacuum-pumping process, we prepare a series of xCo₂Z/PDMS (x = 2; 4; 6; 8; 10) composite films, which are consisted of PDMS matrix and different quantity of micro-sized ferrite particles. XRD pattern indicates that the obtained ferrite particles include Co₂Z main phase and BaM second phase. We demonstrate that 4Co₂Z/PDMS film has improved magnetic-dielectric properties at 800 MHz (μ' = 1.49; ε' = 4.54 tanδ_μ = 0.058; tanδ_ε = 0.008). Also, the film has high saturation magnetization (σ_s = 17.51 emu/g). Furthermore, SEM micrographs show that using ultrasonic stirring and fast curing, the micro-sized ferrite particles are well dispersed in PDMS matrix. Our study, which provides a simple method to improve high-frequency magnetic and dielectric properties of PDMS matrix, could pave the way for development of high-frequency flexible electronics.     

Investigation of dielectric and piezoelectric properties in aliovalent Eu3+-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics

Rare earth (Eu³⁺)-modified Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) polycrystalline ferroelectric ceramics were fabricated by high-temperature solid-state sintering, the phase structure, dielectric and piezoelectric properties were investigated. Eu³⁺ addition was found to significantly improve dielectric and piezoelectric properties of PMN-PT, where the optimized properties were achieved for the composition of 2.5 mol%Eu: 0.72PMN-0.28PT, with the piezoelectric d₃₃ = 1420 pC/N, dielectric ε_r = 12 200 and electromechanical k₃₃ = 0.78, respectively. All these results indicate that the Eu³⁺-doped PMN-PT ceramics are promising candidates for high-performance room-temperature piezoelectric devices.     

Binary polymer blend of ArPTU/PI with advanced comprehensive dielectric properties and ultra-high thermally stability

Flexible high-temperature polymeric dielectrics with advanced dielectric properties are urgently demanded in various applications. In this work, series of polymer blend films were prepared from aromatic polythiourea (ArPTU) and polyimide (PI). The experimental results revealed that the blend films were properly engineered to achieve higher breakdown strength, greater dielectric constant, and larger energy density than pure PI film. For instance, the optimum property was obtained from the blend film with 10 wt% ArPTU, exhibiting prominent dielectric properties (K = 4.52, E_b = 443 MV/m), enhanced energy density (4.00 J/cm³) as well as excellent heat resistance (T_g = 419°C). In addition, stable dielectric properties at broad temperature range from −50 to 250°C were also acquired. It is deduced that the good compatibility from ArPTU and PI with similar polarity are responsible for the improved properties. The superior comprehensive properties which combine the advantages of ArPTU and PI suggest the potential applications of ArPTU/PI blend film in high-temperature dielectric areas.     

High-strength ceramic foams with ultralow dielectric constant and loss in terahertz frequency region

Sixth generation (6G) wireless networks operating in terahertz frequency region are significant solutions to the increasing number of telecommunication devices and the demand for faster data transmission. However, few dielectric materials exhibiting an ultralow relative dielectric constant (ε_r), loss tangent (tanδ), and high mechanical strength are found suited for 6G telecommunication. In this study, we developed lightweight ceramic foams by directly sintering glass hollow spheres. The effects of sintering temperatures on their mechanical performance, and terahertz optical and dielectric properties were systematically investigated. The final compositions of ceramic foams contain glass, cristobalite, quartz, and wollastonite. The crystalline content increases with increasing sintering temperature. The ceramic foams sintered at low temperatures of 700–850°C exhibit a high porosity ranging from 74.6% to 87.3%, ultralow ε_r ranging from 1.41 to 1.83, and tanδ of ∼0.011 at 0.5 THz, as well as high compressive strength ranging from 10.1 to 27.4 MPa, which could be promising materials for 6G telecommunication.     

High dielectric permittivity and percolative behavior of polyvinyl alcohol/potassium dihydrogen phosphate composites

A new kind of anhydrous, transparent, and flexible potassium dihydrogen phosphate (KH₂PO₄ or KDP)/polyvinyl alcohol (PVA) composite in the form of film (0.10 mm) has been prepared by solution casting technique. KDP is well dispersed in the polymer matrix as observed from the microstructural studies. Frequency and temperature dependent dielectric properties of the composites have been studied with varying KDP concentrations. The PVA/KDP composite films exhibited extraordinarily high relative permittivity ε′ ∼ 430 (80 times higher compared with pure PVA and even higher than KDP) near the percolation threshold (ϕ_C = 2.5 wt % KDP) with low dielectric losses (∼ 0.15) at 1 kHz and room temperature. Such flexible, low loss and high dielectric permittivity material has enormous importance for application in devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Structural,thermal and dielectric properties of 2D layered Ti3C2Tx (MXene) filled poly (ethylene-co-methyl acrylate) (EMA) nanocomposites

Light-weight and flexible 2D MXene-based polymer materials with low dielectric loss and high dielectric constant have drawn great attention in the power systems and modern electronic field. A series of Ti₃C₂T_x/EMA composites were fabricated via simple solution casting followed by a compression molding method with various mass concentrations of Ti₃C₂T_x (0, 1, 3, 5, 8, 10, 12, and 15 wt%). Morphological and micro structural properties of the prepared composites were studied via X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM), where the distribution of Ti₃C₂T_x in the Ti₃C₂T_x/EMA composites was confirmed. Thermal behaviors were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) investigations. The DSC analysis reveals that the % of crystallinity decreases from 11.06 with 1 wt% to 5.68 with 15 wt%, where Ti₃C₂T_x acts as an efficient nucleating agent. TGA data confirm the enhancement of the thermal stability of the composites upon increasing in Ti₃C₂T_x loading. The room temperature electrical and dielectric behavior of the studied composites were examined in the frequency range of 100 Hz–5 MHz. In this work, the 10 wt% of Ti₃C₂T_x loaded poly (ethylene-co-methyl acrylate) composite (EMA) showed higher dielectric permittivity (ε′ = 124.22) with lower dissipation loss (tan δ = 0.051) at 100 Hz among all weight percentages. The behavior of charge carriers in the prepared composites was studied by utilizing the impedance spectroscopy technique. The electrical parameters were calculated from the fitted Nyquist plots with a corresponding circuit model. I–V curves confirmed the conduction mechanisms of the composites. This beneficial enhancement in electrical properties recommends the composite can be utilized in flexible electronic storage devices.     

Electromagnetic interference shielding properties of graphene quantum-dots reinforced poly(vinyl alcohol)/polypyrrole blend nanocomposites

Graphene quantum dots (GQDs) reinforced poly(vinyl alcohol) (PVA)/polypyrrole (WPPy) nanocomposite films with various GQDs loadings were synthesized using the versatile solvent casting method. The structural and morphological properties of PVA/WPPy/GQDs nanocomposite films were investigated by employing Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The thermogravimetric analysis revealed enhanced thermal stability of synthesized nanocomposites while enhanced dielectric properties were also observed. The maximum dielectric constant value for PVA/WPPy/GQDs nanocomposite films was observed to be ε = 6,311.85 (50 Hz, 150°C). The electromagnetic interference (EMI) shielding effectiveness (SE) of nanocomposite films was determined in the X-band (8–12 GHz) and Ku-band (12–18 GHz) frequency region. The EMI SE was found to be increased from 0.8 dB for the pure PVA film to 9.8 dB for the PVA/WPPy/GQDs nanocomposite film containing 10 wt% GQDs loading. The enhanced EMI shielding efficiency of nanocomposite films has resulted from the homogenous dispersion of GQDs in PVA/WPPy blend nanocomposites. Thus, the prepared nanocomposites are envisioned to utilize as a lightweight, flexible, and low-cost material for EMI shielding applications.     

Effect of BN content on the structural,mechanical, and dielectric properties of PDCs-SiCN(BN) composite ceramics

Hexagonal boron nitride (h-BN) with low dielectric loss and high temperature resistance opens up new opportunities for the preparation of polymer-derived SiCN ceramics (PDCs-SiCN ceramics) with excellent mechanical and dielectric properties. BN-containing polymer-derived SiCN composite ceramics (PDCs-SiCN(BN) composite ceramics) with different BN content were prepared via a pyrolysis process of ball-milling-blended Polyvinylsilazane/boron nitride (PVSZ/BN) precursors. BN is stably embedded in the SiCN tissue and tightly bound with it. The appropriate content of BN greatly improves the mechanical properties of PDCs-SiCN ceramics, as BN reduces the number of pores and prevents crack expansion. Additionally, BN is also beneficial in lowering the dielectric loss of PDCs-SiCN ceramics because of the weakened polarization relaxation behavior. PDCs-SiCN (BN) composite ceramics have optimal mechanical and dielectric properties when the BN content is 1 wt%. The flexural strength, flexural modulus and compression strength of PDCs-SiCN(BN) composite ceramics with 1 wt% BN doping content were 189.37 MPa, 46.38 GPa, and 399.02 MPa, respectively. Its average dielectric loss (tanδ_ε) at 12.4-18 GHz is 0.0049.     

Co-substituted CuO–ZrO2–Nb2O5 composite ceramics with low-temperature sintering and low-loss for high-performance patch antenna

In the field of microwave dielectric ceramics for patch antennas, it has always been a thorny issue to simultaneously satisfy high dielectric constant, low sintering temperature and low dielectric loss. Here, a CCZN (x = 0.04) composite ceramic with excellent microwave dielectric properties was developed. It can be found that an appropriate amount of Co²⁺ substitution can enhance the compactness, increase the dielectric constant (ε_r), reduce the dielectric loss (tanδ) and enhance the temperature coefficient (τ_f). The composite ceramic with excellent dielectric properties (ε_r = 22.6, Q × f = 37,624 GHz, τ_f = ?64.9 ppm/°C) shows good sintering compatibility with Ag. Based on this composite ceramic, a high-performance patch antenna was designed for Beidou satellite navigation system (BDS). It presents a small size of 30 × 30*3.8 mm³ and excellent radiation performance (return loss = ?32.9 dB, VSWR = 1.047, impedance bandwidth = 60.6 MHz, radiation efficiency = 94.6% and realized gain = 7.704 dB). This work promotes the application of microwave dielectric ceramics in the field of patch antennas.     

Electrical and mechanical properties of BZT − xBCT lead-free piezoceramics

In this study, lead-free (1 − x)Ba(Zr_0.2Ti_0.8)O₃ − x(Ba_0.7Ca_0.3)TiO₃ compositions are synthesized via conventional solid oxide route, and the ceramics are fabricated with normal sintering in air. The effects of composition fluctuations on dielectric, piezoelectric, and mechanical properties are investigated. The phase structure and the microstructure are analyzed with X-ray diffraction and scanning electron microscopy. The best dielectric and piezoelectric properties of ε_r = 11 207 and d₃₃ = 330 pC/N were obtained for BZT−0.35BCT and BZT−0.5BCT ceramics, respectively. The mechanical behavior—in terms of Vickers hardness and compressive and flexural strengths—was investigated, and the best mechanical behavior was found in the vicinity of the phase transition boundary with x values between 0.5 and 0.6.     

Influence of LNO Top Electrodes on Electrical Properties of KNN/LNO Thin Films Prepared by RF Magnetron Sputtering

Highly (001) oriented (K,Na)NbO₃ (KNN) lead‐free piezoelectric thin films were grown on LaNiO₃ (LNO)‐coated silicon by RF magnetron sputtering. The effects of the top electrodes on the electrical properties of KNN thin films were investigated. The dielectric and piezoelectric properties were remarkably improved in LNO/KNN/LNO (ε_r = 899 at 1 kHz, d₃₃ = 58 pm/V), compared with that in Pt/KNN/LNO (ε_r = 584 at 1 kHz, d₃₃ = 26 pm/V). An enhanced ferroelectricity was also obtained in LNO/KNN/LNO, with a remnant polarization of 12 μC/cm² and a maximum polarization of 23 μC/cm² at the applied field of 200 kV/cm. Besides, the temperature dependence of piezoelectricity of the films was characterized in this study.     

Excellent Polyimide Dielectrics Containing Conjugated ACAT for High-Temperature Polymer Film Capacitor

In order to meet the requirements of polymer dielectric materials for high thermal stability and excellent dielectric properties in the application of high-temperature film capacitors, a series of polyimide (PI) films are fabricated by introducing a self-synthesized aniline trimer (ACAT) with a conjugated structure in this work. Since the conjugated ACAT in the main chains of PI improves the electron polarization and carrier mobility of the PI molecular chains, the dielectric constant of the ACAT-PI films is greatly enhanced (4.4–7.4). Meanwhile, the dissipation factor does not increase apparently (0.002–0.013). The dielectric properties are stable even when the temperature is up to 200 °C, the thermal degradation temperature is as high as 450 °C, and the mechanical properties are also excellent (70–105 MPa). Among all the films, the PI film with 5 mol% ACAT exhibits the maximal energy density of 3.6 J cm⁻³ under the field of 426 kV mm⁻¹, the high tensile strength (90 MPa) and the excellent thermal stability (T_d5 = 515 °C). The work paves the way to prepare high-temperature polymer dielectric film materials with high energy storage density.     

Modified BCZN particles filled PTFE composites with high dielectric constant and low loss for microwave substrate applications

The modified 0.7Ba (Co_1/3Nb_2/3)O₃-0.3Ba(Zn_1/3Nb_2/3)O₃ (BCZN) powders filled PTFE composites were synthesized by hot-pressing. The influences of BCZN content on the microstructure, dielectric, thermal, mechanical properties and moisture absorption were investigated systematically. The modified BCZN powders filled PTFE composites exhibited better microstructure and dielectric properties compared with untreated powders. Various mathematic models were utilized to predict the dielectric constant of different composites and the effective medium theory (EMT) showed perfect consistency with the experimental results. The modified BCZN/PTFE composites possess the best comprehensive properties at the powders content of 50 vol% with high dielectric constant (ε_r) of 7.7, low loss (tanδ) of 0.0014, acceptable temperature coefficient of dielectric constant (τ_ε) of −125.6 ppm/°C and temperature coefficient of resonant frequency (τ_f) of 29.4 ppm/°C at 7 GHz, low moisture absorption of 0.07% and low coefficient of thermal expansion (CTE) of 33 ppm/°C. All the results show modified BCZN/PTFE composites are the potential materials for microwave substrate applications.     

Blended graft copolymer of carboxymethyl cellulose and poly(vinyl alcohol) with banana fiber

Conducting hydrogel copolymer was prepared by graft copolymerization of carboxymethyl cellulose (CMC) and boric acid onto poly(vinyl alcohol) (PVA). The dielectric properties of CMC‐g‐PVA/prehydrolyzed banana blend have been investigated as a function of frequency, with special reference to pure prehydrolyzed banana. Also, the static bending for the blend was determined and no abrupt failure was observed. The dielectric properties measured were dielectric constant (ε′), dissipation factor (tan δ), and loss factor (ε″). At high frequencies, a transition in the relaxation behavior was observed, whereby the dielectric constant, loss tangent, and loss factor decreased with frequency. Experimental ε′ values of the blend are greater than those of prehydrolyzed banana. The dielectric behavior depends greatly on the nature of the present group, the crystallinity of the system, and the degree of hydrogen bonding between the different chains. The variation of the dielectric properties was correlated with blend morphology and also to the possibility for interfacial polarization that arises because of the differences in conductivities of the two phases. It was found from the infrared spectra that the incorporation of CMC‐g‐PVA copolymer decreases the crystallinity of the blend and also decreases the degree of hydrogen bonding, which results in a high dielectric constant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1842–1848, 2006     

Design of artificial nacre-like hybrid films as shielding to mitigate electromagnetic pollution

Multifunctional designs of biomimetic layered materials are in great demand for broadening their applications. Artificial hybrid films are fabricated using a simple evaporation-induced assembly method, using nacre as the structural model, two-dimensional reduced graphene oxide (RGO) and magnetic graphene (MG) as inorganic building blocks and poly(vinyl alcohol) (PVA) as glue. The nacre-like films exhibit good mechanical performance, such as high stiffness, strength and toughness. The biomimetic materials possess the shielding properties of electromagnetic pollution. MG based nacre-like films present more significant electromagnetic interference (EMI) shielding performance than RGO film, because of a synergism between dielectric loss of graphene and magnetic loss of magnetic nanoparticles. Average EMI shielding effectiveness (SE) reaches ∼20.3 dB over the frequency range of 8.2–12.4 GHz (X band) for MG hybrid film only 0.36 mm thick. The lightweight, flexible and thin MG artificial hybrid films possess good potential for EMI shielding applications.     

Microwave dielectric properties of (0.75ZnAl2O4–0.25TiO2)–MgTiO3 ceramics prepared using digital light processing technology

ZTM ceramics comprising of 0.75ZnAl₂O₄–0.25TiO₂ and MgTiO₃ at a ratio of 90:10 wt.% are widely used in the field of communication as filters and resonators owing to their excellent microwave dielectric properties. However, the development of such dielectrics with complex structures, as required by microwave devices, is difficult using traditional fabrication methods. In this study, ZTM microwave dielectric ceramics were prepared using the digital light processing (DLP) technology. The influence of the sintering temperature on the phase composition, microstructure, and microwave dielectric properties of ZTM ceramics was investigated. Results showed that with an increase in the sintering temperature, the dielectric constant (ε_r) and quality factor (Q × f) of ZTM ceramics initially increased owing to the increase in the density and diffusion of ions. However, when the sintering temperature was excessively high, the abnormal growth of crystal grains and micropores led to a decrease in ε_r and Q × f. The ZTM ceramics sintered at 1450°C exhibited the optimum microwave dielectric properties (ε_r = 12.99, Q × f = 69 245 GHz, τ_f = −9.50 ppm/°C) owing to the uniform microstructure and a high relative density of 95.02%. These results indicate that DLP is a promising method for preparing high-performance microwave dielectric ceramics with complex structures.     

Dielectric and gyromagnetic structure modulations of Zn–Sn codoped yttrium–iron–garnet based on the density-generalized functional theory and P–V–L bond theory

Herein, the crystal structure, dielectric properties, and gyromagnetic characteristics of Zn–Sn codoped Y₃Zn_xSn_xFe_5−2xO₁₂ (x = 0.0–0.5) prepared using a conventional ceramic process were investigated. According to the first-principles’ calculations and complex crystal bonding theory, Zn²⁺–Sn⁴⁺ codoping can increase the relative dielectric constant (ε_r) by enhancing the average ionicity. The x-ray photoelectron spectroscopy (XPS) and Raman analysis results indicate that an appropriate amount of Zn²⁺–Sn⁴⁺ codoping can help improve the microscopic morphology, maintain the appropriate ratio of divalent iron ions, and reduce the microwave magnetic and electrical losses of YIG ferrites. The optimized microwave properties are as follows. Y₃Zn_0.3Sn_0.3Fe_4.4O₁₂ after sintering at 1400°C; ε_r = 15.6; dielectric loss, that is, tanδ_ε = 4.3 × 10⁻⁴; saturation magnetization, that is, 4πM_S = 2244 G; ferromagnetic resonance linewidth, that is, ΔH = 37 Oe. These properties can help improve the performance of high-frequency microwave components by enhancing the properties of ferrite.     

Low dielectric loss BST/PTFE composites for microwave applications

Ba_0.3Sr_0.475Ce_0.03La_0.12Ti_0.997Mn_0.003O₃/Polytetrafluoroethylene (PTFE) composites were prepared using powder processing technique. The effects of the ceramic filler volume fraction and the coupling agent on the phase composition, microstructure, dielectric and thermal properties of the composites were investigated in this paper. The ceramic filler dispersion in the PTFE matrix, thus the dielectric loss, permittivity, and dimensional thermal stability of the composite was considerably improved by the modification of BST filler surface using phenyl trimethoxy silane (PTMS) coupling agent. Variation of the dielectric permittivity of the composite with composition was well fitted by the effective medium theory (EMT) model in the experimental compositional range. The obtained silane-treated composite with 0.5 V_f BST exhibits extremely low dielectric loss: ε_r = 16, tan δ = 5.4 × 10⁻⁴ @1 MHz and 5.16 ± 0.6 × 10⁻³ @ 10 GHz. The CTE of the composites was reduced to 43 ppm/°C.     

Structure and properties of Bi(Zn½Ti½)O3-modified Pb(Zr,Ti)O3 piezo-/ferroelectric ceramics around the ternary morphotropic phase boundary

To develop high-performance piezo-/ferroelectric materials, Bi(Zn_½Ti_½)O₃–PbZrO₃–PbTiO₃ (BZT–PZ–PT) ternary solid solution with compositions around the morphotropic phase boundary (MPB) is synthesized by solid-state reaction. The crystal structure and electric properties are investigated systematically by X-ray powder diffraction (XRD), dielectric spectroscopy, and ferroelectric and piezoelectric measurements. On the basis of the results of the XRD, dielectric and ferroelectric measurements, the pseudo-binary phase diagram of the yBi(Zn_½Ti_½)O₃–(1 − y)[(1 − x)PbZrO₃–xPbTiO₃] system has been constructed for three series, namely, y = 0.05, 0.10, and 0.15. It is found that the introduction of BZT into the PZT system makes the paraelectric to ferroelectric phase transition more diffuse, brings the MPB to a lower PT content, and enlarges the MPB region. The best properties with an improved dielectric constant ε' = 1248, and a large remnant polarization P_r = 33 μC/cm², as well as a relatively high T_C = 286°C, and a high coercive field E_c = 23 kV/cm was achieved in the y = 0.15 series with MPB composition x = 0.425, making it a promising material for high-power piezoelectric applications.     

Ultra low loss (Mg1 − xCax)2SiO4 dielectric ceramics (x = 0 to 0.15) for millimeter wave applications

(Mg_{1 − x}Ca_x)₂SiO₄ dense ceramics (x ≥ 0.15) were prepared, and their microwave dielectric characteristics were investigated together with the structure evolution. The sintering temperature for Mg₂SiO₄ ceramics was reduced significantly with Ca²⁺substitution. (Mg_{1 − x}Ca_x)₂SiO₄ ceramics exhibited a small increase in dielectric constant (ε_r) correlated with increased crystallite size, and ultra-high quality factor Qf value was achieved throughout the compositional range. Temperature coefficient of resonant frequency (τ_f) was considerably tuned from −70 ppm/°C to −33 ppm/°C, and this improvement was deeply linked with the decreased bond valance. At x = 0.075, (Mg_{1 − x}Ca_x)₂SiO₄ ceramics exhibited the best combination of microwave dielectric characteristics: ε_r = 7.2, Qf = 199,800 GHz at 26 GHz, τ_f = −33 ppm/°C. The present ceramics could be expected as promising candidate of dielectric materials for millimeter wave applications.