High Dielectric Loss Research Articles

Polyetherimide nanocomposites filled with in‐situ synthesised bismaleimide‐DDE@CCTO hybrid nanofibers enabling improved dielectric and interfacial performance

AbstractMost current research of nanocomposite dielectrics for modern electronic devices and electric equipment usually focuses more on dielectric properties while in some extent ignoring the interfacial adhesion characteristics. However, the poor interfacial adhesion frequently results in serious dielectric field distortion, which would in return impair the dielectric performance enhancement. As such, how to simultaneously achieve the excellent dielectric properties and interfacial adhesion performance in organic‐inorganic nanocomposite system is worth in‐depth investigation. To realise this aim, novel hybrid nanofibers are neatly fabricated using in situ copolymerisation reaction of bismaleimide and diamino‐diphenyl ether monomers on the CCTO nanofiller surface via covalent bond connections. The resulting nanocomposites achieve high dielectric constant (9.3) and low dielectric loss (0.0185) at 1 kHz. The BMI‐DDE@CCTO/PEI yields a high discharge energy density (3.09 J/cm3) at moderate electric field (200 MV/m). Noticeably, the nanocomposites enable stable dielectric performance over a wide temperature range from room temperature to 150°C. Moreover, the binding energy for BMI‐DDE and PEI is 1052 kJ/mol according to DFT calculation. As such, the authors speculate this interesting study would inspire the broad researchers devoting to investigating bismaleimide‐coated high‐aspect‐ratio nanofillers and their dielectric materials for collaboratively improved dielectric and interfacial performance.

Enhanced high-temperature energy storage properties in BNT-based ceramics with well-controlled low dielectric loss

High-temperature resistance is one of the hot topics in the development of high-power density dielectric materials. It is still a great challenge for dielectric materials to meet the requirements of high energy density and low energy loss at high temperature. Based on the philosophy of increasing the Curie temperature and decreasing the dielectric loss at high temperature, a ceramic system of (1-x)Bi0.5Na0.5TiO3-xBi(Mg0.3Zr0.6)O3 ((1-x)BNT-xBMZ) is designed to improve the high-temperature energy storage properties. The Curie temperature was significantly increased from 320 °C to nearly 400 °C, and the dielectric loss was controlled below 5% up to 400 °C in the 0.92BNT-0.08BMZ ceramic. Due to the high Curie temperature and low dielectric loss, the maximum polarization and discharge energy density at 200 °C under 200 kV/cm of the 0.92BNT-0.08BMZ ceramic sample are as high as 48.79 μC/cm2 and 3.73 J/cm3, respectively. With the BMZ content increases, the changing rate of Pmax in the temperature range of 30∼200 °C decreases from 18.76% for the x = 0.06 ceramic to 10.27% for the x = 0.10 ceramic under 120 kV/cm, and the remanent polarization decreases from 5.23 μC/cm2 to 2.55 μC/cm2 at 200 °C, correspondingly. All these characteristics show that (1-x)BNT-xBMZ ceramics have broad application prospects in the field of high-temperature energy storage systems.

Structural, Physical, Magnetic, and Dielectric Study of Glassy and Crystalline Bismuth Zinc Silicates

AbstractThe current study aims to thoroughly analyze the optical, magnetic, and dielectric properties of the glass and glass-ceramics in the system Bi2O3.ZnO.SiO2 with stoichiometric composition xBi12SiO20.(100-x)Zn2SiO4(x = 0, 10, 30, 50, 70, 90, and 100). The systematic dependence on density, Bi2O3, and the presence of interphases was studied. Fourier transform infrared (FTIR) spectra of the glass-ceramic samples certify the changes occurring in structure from amorphous to crystalline form where more intense, sharp, narrow bands were observed. Both 10B and 30B samples display more ultraviolet (UV) absorbance than the remaining samples. Upon introducing Bi2O3, the glass sample's color gradually changed from brown to pale yellow. In the vibrating sample magnetometer (VSM) study, the highest (9.22 × 10-7 emu/g) and lowest (4.53 × 10-7 emu/g) magnetic susceptibility were noticed for 30B and 70B samples, respectively. Further, all glass ceramics display diamagnetic properties due to the existence of Bi ions. The glass-ceramic samples showed better dielectric properties than glass samples due to changes from the amorphous nature of the glassy phase (high dielectric loss) to the well-ordered structure of the corresponding glass-ceramic (low dielectric loss). The glass ceramic sample of 100B attained much lower dielectric loss values (0.002, f = 106 Hz) than the corresponding glass sample (0.01, f = 106Hz) which could be helpful for electric storage devices, i.e. capacitors, supercapacitors, batteries, etc. Besides, the high-quality factor (Q = 2758) of the same glass-ceramic sample makes it promising in Radio Frequency (RF) circuits or other high- frequency applications.

Comparative assessment of the qualities of commercial and synthetic transformer oils

Petroleum transformer oils previously produced in the USSR met the requirements of ГОСТ 982-80. Balakhany oil and Dossor low-paraffin oil of the Emben field were the raw materials for obtaining transformer oil. The composition of transformer oils is taken into account when choosing raw materials and their regeneration. Т-1500у – transformer oil of improved quality, is used in electrical equipment up to 500 kV and up to 750 kV. ГК oil is a hydrocracking transformer oil, used in voltages up to 1150 kV, contains ionol. Тсп is oil from West Siberian oils, used up to 220 kV. This oil is of relatively low quality, characterized by a high sulfur content, low oxidation stability, and high dielectric loss tg. In the Institute of Petrochemical Processes, research has been carried out on the selective purification of transformer oil distillate from Balakhany oil using a new highly effective solvent – ionic liquid (IL) – a quaternary ammonium salt of formic acid and a number of amines – morpholine, aniline or di-, triethylamines. The optimal conditions for the selective purification of the distillate have been developed. Due to the shortage of high-quality transformer oils, as well as the high cost, in recent years, oils have been imported from Sweden and Austria. An ionic liquid as a solvent is highly selective and selective. The analysis of the extract from selective purification showed that it does not contain naphthene-paraffins, the content of aromatic hydrocarbons in the extract is 65 %, and when purified with furfural it is 40.8 %. The ionic liquid is environmentally friendly.

Effect of rare earth substitution on electromagnetic and microwave absorption properties of nickel-cobalt nano ferrite

Oxygen vacancy engineering is one of the most effective strategies for tuning the microstructural properties of oxide nanomaterials. However, the connection between oxygen vacancies and electromagnetic (EM) wave absorption capacities is unclear. Herein, oxygen vacancy-boosted microwave absorption is realized over Gd-doped Ni0.5Co0.5Fe2O4 (NCFO) nanoceramics. All magnetic properties are studied with the influence of induced lattice strain. Except for Ni0.5Co0.5 Gd0.075Fe1.925O4 (NCFOG3), which has an elevated saturation magnetization (Ms) of 63 emu/g, the Ms decreases with increasing Gd content. In addition, remnant magnetization (Mr), coercivity (Hc), and anisotropic constant (K) increased until Ni0.5Co0.5 Gd0.050Fe1.95O4 (NCFOG2) and then declined. The EM wave parameters: dielectric permittivity (ϵ'), magnetic permeability (μ'), dielectric loss (ϵ''), and magnetic loss (μ'') are systematically examined and found in the ranges of 2.07–3.5, 1.73–4.7, (4 × 10-2) – (2.2 × 10-1) and 0.18–0.35 respectively. Our finding shows that a small amount of Gd favors the high oxygen vacancy concentration, an appropriate lattice defect, and high magnetic and dielectric losses. The possible mechanism for EM wave absorption revealed the largely localized electrons and dipole centers created by the numerous oxygen vacancies causing the multiple reflection and scattering, which enhanced conductive loss, defect, and dipole polarizations. The maximum reflection loss (RL) -28.37 dB is observed at 17.80 GHz of a 2 mm thick sample for NCFOG3. This research reveals a distinct link between oxygen vacancy defects and EM wave dissipation capability, providing important information for developing better EM wave absorbents.

Engineering DyCrO3 ceramics toward room-temperature high-κ dielectric applications

The search for a high-κ dielectric material that combines a high dielectric constant (ϵ′) and low dielectric loss is very crucial because of its widespread use in gate dielectrics to avoid the leakage current that arises due to continued miniaturization of present SiO2-based metal-oxide semiconductor field-effect transistor devices. RCrO3 (R is a rare-earth ion) materials have been at the center of interest because of their intriguing ferroelectric and magnetic properties, as well as their room-temperature colossal dielectric constant (CDC) values. Although CDC (ϵ′∼104) in RCrO3 materials is quite common, it is unsuitable for device applications since it is associated with a larger dielectric loss value (tan δ∼7 at 11 kHz). Here we have focused on polycrystalline DyCrO3, prepared using multiple synthesis techniques, and thoroughly investigated the origin and tuning of the various dielectric relaxations that give rise to CDC and large dielectric loss values. A clear understanding of the origin of dielectric relaxations enables us to design a specially synthesized DyCrO3 (SPS-DCO) in which the extrinsic dielectric relaxations driven large dielectric loss values can be completely suppressed and which is found to be associated with optimized high-κ dielectric properties [ϵ′∼130, tan δ∼0.06, and temperature coefficient of dielectric constant (TCϵ) ∼ 2280 ppm/K at 11 kHz, 300 K]. The only remaining intrinsic Debye-type dielectric relaxation in SPS-DCO arises due to electric-field-assisted charge hopping among various valences of Cr (investigated using x-ray photoelectron spectroscopy) that presently limits the lowest attainable loss value.

Progress of Polymer-Based Dielectric Composites Prepared Using Fused Deposition Modeling 3D Printing.

Polymer-based dielectric composites are of great importance in advanced electronic industries and energy storage because of their high dielectric constant, good processability, low weight, and low dielectric loss. FDM (Fused Deposition Modeling) is a greatly accessible additive manufacturing technology, which has a number of applications in the fabrication of RF components, but the unavoidable porosity in FDM 3D-printed materials, which affects the dielectric properties of the materials, and the difficulty of large-scale fabrication of composites by FDM limit its application scope. This study's main focus is on how the matrix, filler, interface, and FDM 3D printing parameters influence the electrical properties of FDM-printed polymer-based dielectric composites. This review article starts with the fundamental theory of dielectrics. It is followed by a summary of the factors influencing dielectric properties in recent research developments, as well as a projection for the future development of FDM-prepared polymer-based dielectric composites. Finally, improving the comprehensive performance of dielectric composites is an important direction for future development.

Dielectric and Humidity Sensing Properties in Iron Nanoparticle Substituted Polyaniline Composite

The existence of graphene-based Polyaniline nanocomposite has been demonstrated to be exceptional host matrices for entrapping nano-sized particles, and its composites are widely used in a variety of applications such as transducers, sensors, electrodes, microwave absorption, and thermoelectric applications. The purpose of this study is to investigate the dielectric properties and humidity sensing response of a Fe doped PANI/Graphene (PAFG) composite synthesized in-situ polymerization using adhathoda vasica plant extract. The FT-IR, XRD, and SEM-EDX techniques were used to characterize the sample. The dielectric measurements were performed at 298K over a wide frequency range 5x101 to 5x106 Hz. Humidity response studies were performed at room temperature. Iron nanoparticles distributed homogeneously in the PANI matrix were ascertained from IR spectral data. At room temperature, the dielectric properties of the synthesized DS-4 powder outperform those of the synthesized pristine PANI and Fe nanoparticles, with superior dielectric constant and high dielectric loss. When the synthesized iron decorated composite was exposed between 10% and 97% RH, the electrical resistance decreased, which is attributed to the polarization process affecting electrical conductivity within these materials. The PAFG-40% composite exhibited high sensitivity at low humidity levels ranging from 30% to 70% RH.

The Effect of Hydrothermal Temperature and Sample Thickness on the Synthesis of BaFe<sub>12</sub>O<sub>19</sub>@MnO<sub>2</sub> Core-Shell Composites

Advances in radar technology today are experiencing rapid development based on the latest findings that complement each other. BaFe12O19 is a type M hexagonal ferrite material as the best candidate for absorber material applications. Manganese dioxide (MnO2) is a transition metal that has a high dielectric loss and has the opportunity to increase the absorption of electromagnetic waves. The BaFe12O19@MnO2 core-shell composite produces the combined characteristics of BaFe12O19 and MnO2, which can improve performance as radar-absorbing material. The BaFe12O19@MnO2 core-shell composite is synthesized in two stages: molten salt synthesis in manufacturing BaFe12O19 as a core and hydrothermal synthesisto grow MnO2 nanoflowers as a shell. The research objective was to produce BaFe12O19@MnO2 core-shell composite for radar absorbing applications in the x-band with absorption of ~99%. In molten salt synthesis, using two calcination operations at 1000 °C for two hours to create BaFe12O19 as a template, then combining BaFe12O19 template with Fe2O3 and BaCl2.2H2O for eight hours at 1100 °C prepared for MnO2 pathways on the BaFe12O19 surface. Hydrothermal synthesis occurs by dissolving BaFe12O19 and KMnO4 in deionized water with a mass ratio of BaFe12O19 to KMnO4 is 1:1, followed by hydrothermal synthesisat a holding time of 12 hours with a temperature of 150 °C; 170 °C; 190 °C. Characterization of vector network analysis on a variation of sample thickness (1; 1.5; 2; 2.5; 3) mm were analyzed in the x-band frequency on 8-12 GHz. BaFe12O19@MnO2 core-shell composite was hydrothermally produced at 170 °C with a particle size of 197.1 nm, a thickness of 2.5 mm, and a reflection loss of -20.31 dB at 8.7 GHz. The absorber material from the combined synthesis of molten salt and hydrothermal synthesis to make BaFe12O19@MnO2 core-shell composite successfully produced microwave absorption up to 99.06%.

Partially unzipped carbon nanotubes-CaCu3Ti4O12/ferroelectric polymer nanodielectric composites with high permittivity, high energy storage capacity and low dielectric loss

Partially unzipped carbon nanotubes-CaCu3Ti4O12/ferroelectric polymer nanodielectric composites with high permittivity, high energy storage capacity and low dielectric loss

Functional additive manufacturing of large-size metastructure with efficient electromagnetic absorption and mechanical adaptation

Broadband microwave absorption as a hot research topic plays important roles on electromagnetic compatibility, electromagnetic radiation protection and radar detection disguise. However, traditional molding method is difficult to fabricate large-size curving structures for broadband microwave absorption. Herein, the material extrusion with high-speed printing process was effective to manufacture large-size metastructures for broadband microwave absorption. The polylactic acid was mixed and extruded with nano pyrolytic carbon in high temperature to manufacture functional filaments with high dielectric loss. The printed metastructure integrated with 0.5 mm quartz fiber reinforced composite (QFRC) achieved -10 dB broadband microwave absorption in 3.03-18 GHz and effective load bearing performance in tensile and flexural tests. Severe impedance mismatch brought by QFRC was overcome by appropriate structure design and high-speed printing technique. The proposed design-manufacturing closed loop is a promising approach to fabricate aircraft skin with broadband microwave absorption performance and suitable aerodynamic properties for heavy unmanned aerial drones.

Energy Storage Performance and Dielectric Properties of Surface Fluorinated BOPP Films

Various composite films with high energy storage performance and/or dielectric strength have been fabricated. However, due to some reasons, few of them have been used in practice, and BOPP film is still regarded as the state-of-the-art capacitor dielectric film. Previous work has indicated that direct fluorination can improve the dielectric strength of BOPP films. Herein, as a continuation of previous work, the energy storage performance and basic dielectric properties of the surface fluorinated BOPP film are investigated. The charge-discharge experimental results show that the surface fluorinated BOPP sample has the maximum energy storage or release density of 5.27 or 4.43 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which is 59.8% or 44.6% higher than that of the virgin BOPP sample. The dielectric measurement results indicate that the surface fluorinated BOPP sample has slightly higher dielectric constant and dielectric loss than the virgin BOPP sample. The analyses of physicochemical characteristics reveal that the 0.75 μm thick fluorinated surface layer has a high degree of fluorination. The results of the calculation based on the three-layer dielectric model and the dielectric measurements further show that the fluorinated surface layer has high dielectric constant and loss factor, similar to non-perfluoropolymers. The enhancement of energy storage performance and dielectric strength is mainly attributed to the blocking of the fluorinated layer to electron injection from the cathode, due to a 60% reduction of the interfacial electric field and a decrease in free volume of the surface layer by the fluorination.

Dielectric, structural and absorption properties of Mg2+ substituted Ba2Zn2X hexa-ferrites for microwave devices and applications

Electromagnetic devices have hazardous effects to the environment in the form of pollution. Materials having higher reflection loss and good absorption properties can overcome this pollution. This study synthesizes the Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.1, 0.2, 0.3, and 0.4) using sol-gel method. The higher value of reflection loss of prepared samples was successfully achieved which can be used for absorption applications. X-ray diffraction patterns show a x-type hexagonal phase with crystallite's size ranged from 18 to 43 nm. All the vibrational bands shifted by changing the substitution in all compositions. Six distinct peaks in Raman spectra are located at positions 62, 174, 332, 408, 525, and 673 because of the molecules' phonon vibrations. The peaks were found in the XPS spectrum mode range of 1350-1 eV. All substitutions had a high dielectric constant, dielectric loss, and tan loss at low frequencies, but this value decreased as the frequency increased. The Cole-Cole plots and complex impedance spectroscopy revealed that grain boundary contributed for most dielectric responses. For these materials, cole-cole plots showed a complete semicircle, demonstrating the grain boundary resistance within the samples. Mg substituted Zn-X ferrite with RL of −69.3, and −62.0 dB are found to have excellent microwave absorption properties. The prepared samples could be used for absorption and super-capacitor applications.

Smallest form-factor multi-stacked ceramic patch antenna on package for 5G millimeter-wave mobile applications

A new design for a 5G millimeter-wave array antenna that is only 2.8 mm wide, using multi-stacked high-temperature ceramic substrates, is proposed in this paper. The antenna is designed to meet the requirements for esthetically pleasing and ergonomic smartphone designs and efficient component installations. To overcome challenges posed by the high relative permittivity and dielectric loss tangent of the ceramic substrates, the authors use a polymer adhesion layer with an air cavity and U-shaped probe feeding structures. The resulting 1 × 5 ceramic array antenna has a −10 dB impedance bandwidth in the low-band range of 24.25–28.35 GHz and the high-band range of 37–40 GHz, which covers the 5G New Radio frequency ranges n258, n260, and n261.

Effective dielectric attenuation for excellent microwave absorption with broadband response of carbon hollow microspheres derived from resin

Carbon hollow microspheres as microwave absorption materials (MAMs) are of great significance in the research focuses owing to their lightweight, good impedance matching, and modifiable dielectric properties. However, it is still a huge challenge to distinguish the contribution of dielectric attenuation between carbon intrinsic feature and hollow structure due to the lack of appropriate model materials. Then, the inadequate analysis of effective dielectric attenuation resulted in the construction of carbon hollow microspheres semiempirical and often lacked precise modification of microstructure. Herein, a series of carbon hollow microspheres with controllable graphitization and thickness of shell derived from phenolic resin coated on polystyrene microspheres that fully decomposed were synthesized, which is free of the impact of template residue. The carbon fragments ground from hollow microspheres exhibit the same broadband response as hollow microspheres, with effective bandwidth (RL ≤ –10 dB) of 7.6 GHz, while their electromagnetic wave loss mechanisms are distinct. The high dielectric loss of carbon fragments with the same intrinsic characteristics as carbon hollow microspheres is mainly caused by dipole polarization relaxation and enhancement of electrical conductivity ascribed to overlapping between carbon sheets. For the hollow structure, in addition to dipole polarization relaxation attributed to carbon intrinsic feature, the effective dielectric loss is also comprised of the interfacial polarization in advantage due to the effective heterogeneous interface between air and carbon shell. This work provides a simplified model to clarify the effect of carbon intrinsic feature and microstructure on the dielectric loss of carbon hollow microspheres.

Improvement of dielectric properties and thermal stability of CaCu3Ti4.2O12 ceramics for X8R type capacitors via Co2+ doping

Work on giant dielectric CaCu3Ti4O12 (CCTO) ceramics has been continuously ongoing to obtain materials with a high dielectric constant (ε') and low dielectric loss tangent (tanδ) with both values stable over a wide temperature range. Various methods have been used to modify the materials, such as doping and co-doping with different transition metals at Ca or Cu sites, molar variation of metals (Cu, Ca and Ti), including altering in the methods and conditions of ceramic preparation. In general, the most common problem found in this type of research is that increasing ε' also increases tanδ. Thus, in this work, a one-step polymer pyrolysis (PP) procedure was used to obtain Co2+-doped CaCu3-xCoxTi4.2O12 (x = 0.00, 0.03, 0.05, and 0.07) powders. Then, all powders were sintered to obtain ceramics using two different sintering conditions, 1050 °C for 10 h and 1080 °C for 5 h. The influence of Co2+ ions and sintering conditions on the microstructure, dielectric properties and thermal stability of CaCu3Ti4.2O12 ceramics was investigated. Substitution of Co2+ ions at Cu sites can reduce tanδ values and increase ε' in samples with x = 0.03 and 0.05. However, the tanδ and ε' values were concurrently reduced for x = 0.07. Remarkably, a ceramic with x = 0.07 sintered at 1080 °C for 5 h exhibited very low tanδ(∼0.009) and colossal ε' (∼11551) at 1 kHz and 30 °C, over a broad temperature range (−60 to 150 °C), with stability of Δε' ≤ ±15 %. This ceramic is a suggested candidate material for X8R capacitors. Moreover, increasing the Co2+ doping level could significantly raise the nonlinear coefficient (α) of the ceramics from ∼ 3.48 to 34.30. Additionally, the very high Eb values of ceramics with x = 0.07 sintered at 1050 °C for 10 h and 1080 °C for 5 h were significantly increased by ∼26.34 and 17.45 times, respectively, compared to an undoped ceramic. A widened temperature range where Δε' ≤ ±15 % and tanδ < 0.05 in all ceramics with increasing Co2+ concentration is likely a result of increased grain boundary resistance.

Primary standard for complex units of permittivity at frequency range 0.1–178.4 GHz GET 110-2023

The article is dedicated to research in the fi eld of measuring the dielectric parameters of materials. The aim of the research is to study promising methods for measuring the complex dielectric permittivity of weakly absorbing materials in the decimeter wavelength range, as well as the non-resonant method for measuring the dielectric parameters of materials with high dielectric losses. In order to achieve the set goal of improving the state primary standard of complex dielectric permittivity in the frequency range from 1 to 178.4 GHz, tasks were set to expand the frequency range to 0.1 GHz and the range of reproducible values of the dielectric loss tangent to 10–1. As a result of the improvement, new equipment was introduced into the composition of the standard, and new measurement methods were developed. To measure the complex dielectric permittivity of weakly absorbing materials in the decimeter wavelength range, a resonant measurement method in a coaxial resonator with a shortening capacitive gap and a measurement method in a bulk H011-resonator with dielectric fi lling were developed. To measure elevated dielectric losses up to 10–2–10–1, a measurement method using a non-resonant measuring transducer based on a shielded dielectric waveguide with a measured dielectric sample as such a waveguide has been developed. The developed methods are applied in the Primary standard of complex dielectric permittivity in the frequency range from 0.1 to 178.4 GHz, GET 110-2023. The frequency range of the standard is 0.1–178.4 GHz, the range of reproducible values of relative dielectric permittivity is 1.2–500, dielectric loss tangent 10–8–10–1. The scope of application of GET 110-2023 is metrological support of dielectric control in production of radio frequency cables, telecommunication equipment, electronic components, etc.

Grafting Amino Groups onto Polyimide Films in Flexible Copper-Clad Laminates Using Helicon Plasma.

Polyimide (PI) films are widely used in electronic devices owing to their excellent mechanical and electrical properties and high thermal and chemical stabilities. In particular, PI films play an important role in flexible printed circuit boards (FPCBs). However, one challenge currently faced with their use is that the adhesives used in FPCBs cause a high dielectric loss in high-frequency applications. Therefore, it is envisioned that PI films with a low dielectric loss and Cu films can be used to prepare two-layer flexible copper-clad laminates (FCCLs) without any adhesive. However, the preparation of ultra-thin FCCLs with no adhesives is difficult owing to the low peel strength between PI films and Cu films. To address this technical challenge, an FCCL with no adhesive was prepared via high-power helicon wave plasma (HWP) treatment. Field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) were tested. Also, the surface roughness of the PI film and the peel strength between the PI film and Cu film were measured. The experimental results show that the surface roughness of the PI film increased by 40-65% and the PI film demonstrated improved adhesion (the peel strength was >8.0 N/cm) with the Cu film following plasma treatment and Cu plating.

Fabrication and Characterization of Dielectric ZnCr2O4 Nanopowders and Thin Films for Parallel-Plate Capacitor Applications.

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10-4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

Characterization of dielectric properties of residual ashes obtained from rice husk and annoni grass

This paper presents a study about the characterization of dielectric properties (dielectric constant {varepsilon }_{r} and dielectric-loss constant mathrm{tan}delta) of samples derived from two different biomass types: rice husk ash (RHA) and annoni grass ash (AGA).The procedure is carried out using the resonant cavity method along with a vector network analyzer. For this purpose, four different ashes were produced, by burning rice husk and annoni grass at two different temperatures and burning times: 400 °C/30 min (RHA40030 and AGA40030) and 800 °C/5 h (RHA8005h and AGA8005h). These ashes were combined with Bakelite to produce cylindrical samples with diameter of 30 mm and thickness of 4.5 mm, which were characterized considering the frequency in the test band for 5G technologies ({f}_{o}=3.5 GHz). Experimental results showed that the samples burnt at high temperature showed very high mathrm{tan delta } when compared to the samples burnt at low temperature, mainly for AGA8005h. These values are mathrm{tan delta }= 0.1690 and 1.4900 for RHA8005h and AGA8005h, respectively. The resulting dielectric constants are {varepsilon }_{r} = 3.87 for RHA8005h and {varepsilon }_{r} = 15.14 for AGA8005h). These very high dielectric loss tangent, indicate that these materials exhibit formidable properties for electromagnetic energy absorption, hence allowing the application as radiation-absorbent material (RAM).