Dielectric Constant Stability Research Articles

Enhanced temperature stable dielectric property and energy-storage performance of (1-x)(0.66Bi0.5Na0.5TiO3–0.34Sr0.7Bi0.2TiO3)– xK0.5Nd0.5TiO3 lead-free relaxor electroceramics

In this study, (1-x)(0.66Bi0.5Na0.5TiO3–0.34Bi0.2Sr0.7TiO3)–xK0.5Nd0.5TiO3 (BNBST–xKNT) ceramics were designed and synthesized, and they present significantly enhanced dielectric temperature stability and energy storage properties. The BNBST–0.06KNT composition exhibits a remarkable dielectric stability, as reflected in its stable dielectric constant (△ԑ/ԑ150 °C < ±15%) over a broad temperature range (25–401 °C). BNBST–0.02KNT achieves a high energy storage density Wrec = 1.2 J/cm3 under 110 kV/cm with an energy storage efficiency η of 76.9%, and the improved energy storage property originates from the improved breakdown field strength and decreased hysteresis behavior. The electrical conductivity and relaxation behaviors of BNBST–xKNT were also analyzed via impedance spectroscopy.

High and Temperature‐Independent Dielectric Constant Dielectrics from PVDF‐Based Terpolymer and Copolymer Blends

AbstractRelaxor ferroelectric polymers exhibit high k at their structural phase transition around room temperature. They are particularly attractive as gate dielectric in organic field effect transistor (OFET). Nevertheless, their applications are limited due to their low thermal stability. A polymer blend system with a high and thermally stable dielectric constant is demonstrated by mixing terpolymer poly(vinylidene fluoride‐trifluoroethylene‐chlorofluorethylene) P(VDF‐ter‐TrFE‐ter‐CFE) with copolymer poly(vinylidene fluoride‐trifluoroethylene) P(VDF‐co‐TrFE). PVDF‐based blends of various compositions are characterized by dielectric spectroscopy, differential scanning calorimetry (DSC), infrared spectroscopy, small and wide angle X‐ray scattering (SAXS and WAXS), and atomic force microscopy (AFM) in order to investigate the relationship between morphology and crystallization of the blend and their dielectric properties. An optimized blend of P(VDF‐ter‐TrFE‐ter‐CFE) [55/37/8] and P(VDF‐co‐TrFE) [46/54] at a ratio of 70/30 is found to exhibit a quasi‐constant dielectric constant of 40 ± 2 over a wide temperature range (20–80 °C). Furthermore, electrical characteristics of the PVDF‐blend‐based gate dielectric OFET show further thermal stability in comparison to OFET based on high‐k terpolymer P(VDF‐ter‐TrFE‐ter‐CFE) [55/37/8]. An improvement of their drain current stability by up to 60% is demonstrated at 60 °C. These findings enable broader applications of fluoropolymers in organic electronics.

A Wearable Flexible antenna integrated on a Smart Watch for 5G Applications

This paper presents a design of dual-band flexible wearable antenna for modern 5G applications to integrate on a smartwatch. This antenna is a rectangular antenna which the patch and the ground etched on new flexible material is called “ULTRALAM® 3850HT”. This material is characterized by thin flexible cores with low and stable dielectric constant, which is a key requirement for high frequency and wearable designs. The dielectric constant εr is equal to 3.14, and loss tangent tanδ is equal 0.005 of the ULTRALAM® 3850HT flexible material. The presented antenna is designed to operate at 38 GHz and 60 GHz. The SAR (specific absorption ratio) is also introduced and SAR results will be shown. The presented antenna with and without the smartwatch are simulated using HFSS and CST 2018.

Ba and Mg co-doping to suppress high-temperature dielectric loss in lead-free Na0.5Bi0.5TiO3-based systems

In this study, Ba, Mg co-doped BNT-based ferroelectric ceramic (Ba0.2Na0.3Bi0.5)Ti0.9Mg0.1O3 is fabricated by conventional solid-state reaction to obtain high-temperature dielectric performance. The temperature dependent dielectric constant and dielectric loss are investigated to understand the high-temperature dielectric behavior of the ceramic. The results show that Ba, Mg co-doped BNT ceramic has a very low dielectric loss (about 0.006–0.023) in a wide temperature range of 200–400 °C with dielectric constant about 3200–3800. The complex impedance plots, temperature dependent conductivity and first principle results reveal that the low dielectric loss at high-temperature is mainly due to the Ba doping increases the migration barrier energy of oxygen ions in BNT. The oxygen ion conduction of BNT-based ceramics is restrained, so that the dielectric loss reduces significantly. The study provides a new BNT-based material with low dielectric loss and temperature- stable dielectric constant in a wide temperature range which has great value of high-temperature applications.

Fabrication, structure, and frequency-dependent electrical and dielectric properties of Sr-doped BaTiO3 ceramics

Lead-free strontium-doped ferroelectric ceramics with the compositional formula Ba1-xSrxTiO3 (barium strontium titanate, BST) at (x = 0, 0.25, 0.3, and 0.35) are effectively synthesized through a solid-state reaction. The as-prepared samples are characterized by X-ray diffraction (XRD) and Raman spectroscopy. Further dielectric properties and impedance are examined in detail. XRD and Raman studies reveal that the lattice constant, unit cell volume along with tetragonality ratio change with the Sr concentration, Curie temperature (Tc), and dielectric constant along with dielectric loss factor decrease with increasing Sr2+ ions in BST. A stable dielectric constant is detected in a wide frequency range of 1–1000 kHz. Curie–Weiss law and theoretical estimations indicate a large difference in structural disorder in BaTiO3 (barium titanate, BT) ceramics. Consistent with applied temperature and frequency, a noteworthy change is observed in dielectric constant and loss tangent behavior between lowly and highly doped BT samples. Diffusivity decreases with the increase in Sr2+ amount up to x = 0.3. The relaxation response in BST ceramic is observed for higher values of x. Impedance spectroscopy reveals those oxygen vacancies (OVs) are responsible for conduction in BST ceramics. This study is a systematical investigation on the relationship among the structure, dielectric, and impedance properties of Sr2+ substituted BT ceramics.

Modification on glass fiber surface and their improved properties of fiber-reinforced composites via enhanced interfacial properties

For fiber reinforced composite laminates, properties of laminates can be significantly affected by interfacial properties. In this work, a kind of phthalonitrile containing aromatic ether nitrile linkage (PEN-BAPh) was applied to modify glass fibers (GFs). Cured PEN-BAPh on GFs surface were investigated by Fourier transform infrared spectroscopy (FT-IR) and Ultraviolet–visible spectroscopy (UV–Vis). Scanning electron microscope (SEM) and thermogravimetry (TGA) testing were also applied to confirm the modification. Then, modified fiber-reinforced phthalonitrile-based resin composite laminates were fabricated. As the results indicated that all of the composite laminates showed improved flexural strength, flexural modulus and glass transition temperature (Tg = 296.8–299.6 °C). Improved interfacial adhesion was also studied via interlaminar shear strength (ILSS), impact strength test and monitoring the fracture surfaces. Stable dielectric constants, relative low dielectric loss and outstanding thermal stability (T5% > 350 °C) were obtained for designed composite laminates.

Improved electrical performance of MgO-modified CaCu3Ti4O12 ceramics

Colossal permittivity material CaCu3Ti4O12 (CCTO) ceramics modified by MgO with the mass fraction of 0%, 0.5%, 1%, and 2% were synthesized using a sol-gel method followed by a conventional ceramic preparation process. The scanning electron microscope exhibits that all CCTO ceramics possess the high densities and large grain size. The results of dielectric measurement show that all the samples possess giant dielectric properties. The colossal dielectric constant of CCTO ceramics increases firstly and then decreases with the increase of mass fraction from 0% to 2% at room temperature, while the value of dielectric loss is opposite. Specifically, the sample with the mass fraction of 1% shows the highest density, largest grains and most obvious grain boundaries. 1% sample also shows better electrical properties with giant dielectric constant (~6.59 × 104 at 1 kHz) and low dielectric loss (~0.06 at 1 kHz) at room temperature. In addition, the optimal sample with the mass fraction of 1% shows a more stable dielectric constant from 20 °C to 200 °C. The electrical properties of the CCTO ceramics have achieved good performance by the addition of MgO.

Thickness-dependence of growth rate, dielectric response, and capacitance properties in Ba0.67Sr0.33TiO3/LaNiO3 hetero-structure thin films for film capacitor applications

This work reports the structure, growth rate, dielectric response, and capacitance properties of (100)-oriented Ba0.67Sr0.33TiO3 (BST)/LaNiO3 (LNO) hetero-structure thin films with varied BST layer thicknesses from 34 nm to 342 nm. The BST/LNO hetero-structure thin films were prepared by radiofrequency magnetron sputtering technique on Pt/SiO2/Si substrates. The XRD results showed that the compressive stress is relaxed at around 73 nm of BST layer, and above 119 nm of the BST layer thickness, the tensile stress has a significant effect on the crystal structure of the BST/LNO hetero-structure film. The growth rate of the BST films was thickness-dependent which was strongly related to the minimization of the strain energy. The dielectric constant of BST layer with the compressive stress increase from 177 to 2640 with the increase of BST layer thickness. The BST layer with the tensile stress showed a comparably stable dielectric constant of 2400. In addition, the capacitance properties and the electrical breakdown strength of BST/LNO hetero-structure thin films are also thickness-dependent, respectively. The electrical breakdown strength reached a maximum value of 1237 kV/cm in the BST/LNO hetero-structure thin film with ~73 nm BST layer.

A strategy for design of non-percolative composites with stable giant dielectric constants and high energy densities

Materials with high dielectric constants can be fabricated into electrostatic capacitors for energy storage. Traditional percolative dielectrics such as epoxy/Ag and BaTiO3/Ni have limited energy densities due to the limited breakdown strengths. Here, a strategy for design of non-percolative composites is reported having stable giant dielectric constants and high breakdown strengths simultaneously, and thus, exhibiting high energy densities. A composite is fabricated by using a core-shell type Ag@BaTiO3 fillers where the BaTiO3 shell helps to completely separate the Ag cores with other cores in a sintered BaTiO3 matrix. The composite possesses a stable giant dielectric constant (εr~51,800, εr/εm = 15.6) over wide ranges of frequencies and temperatures while retaining a small dielectric loss (tanδ < 0.02) and a high breakdown strength (Eb > 43 kV cm–1). With the giant εr and the high Eb, the composite exhibits a high energy density (Ue~4.35 J cm–3) which is much enhanced compared with that of percolative composites and neat BaTiO3. Our comparative study with existing composite models reveals that the dielectric behavior in this composite is governed by an interfacial polarization mechanism rather than the power law for percolative dielectrics. This study successfully demonstrated very high k, Eb and energy density of a BT composite by incorporating Ag@BaTiO3 core-shell fillers.

Effect of PbO–B2O3–BaO–SiO2 glass additive on dielectric properties of Ba0.5Sr0.5TiO3 ceramics for radio-frequency applications

In this work, the effects of PbO–B2O3–BaO–SiO2 (PBBS) glass addition (in increasing wt%) into Ba0.5Sr0.5TiO3 (BST0) ceramic on sintering, phase, and dielectric properties of BST0 are studied. The Ba0.5Sr0.5TiO3 (BST0) ceramic was synthesized by the conventional solid-state reaction method, and the PbO–B2O3–BaO–SiO2(PBBS) glass was formed by melting and quenching process. The PBBS glass with different weight percentages (3, 5, 8 and 10 wt%)is added to BST0 ceramic (BST3, BST5, BST8, and BST10, respectively) as a sintering aid to reduce the sintering temperature. Addition of glass helps in better sintering at lower temperatures with the presence of liquid phase at the respective sintering temperatures. The results of liquid phase-sintered ceramics are compared with the BST0 ceramic sintered at 1523 K. The BST10 with 10 wt% glass showed the lowest sintering temperature of 1148 K. Rietveld refinement analysis of BST0 ceramic confirmed the formation of single phase with cubic crystal structure. X-ray diffraction patterns of all liquid phase-sintered ceramics showed that the glass has minimal reaction with the BST0 ceramic and does not affect the crystal structure. Dielectric characterization was performed within the temperature range 20–450 K and frequency range 1 kHz to 1 MHz. It is revealed that the transition temperature shifted with different weight percentage of glass addition. All the compositions exhibit the paraelectric phase at room temperature. Dielectric properties were also measured in the microwave frequency range 8.5–11 GHz at room temperature. BST10 shows the stable and highest dielectric constant (average value of εr = 27) with lowest dielectric loss (tanδ = ∼0.121). Fourier transform infrared (FTIR) and Raman spectroscopy confirmed the formation of desired compositions by detecting molecular vibrations and chemical bonding. The synthesized ceramic is a low-cost candidate and can have potential uses in the radio-frequency applications.

Structural, dielectric and ferroelectric studies of thermally stable and efficient energy storage ceramic materials: (Na0.5-xKxBi0.5-xLax)TiO3

The structural, dielectric and ferroelectric properties of lead-free (Na0.5-xKxBi0.5-xLax)TiO3 (0 ≤ x ≤ 0.12) powders synthesized by modified sol-gel method was investigated. Rietveld refinement of synchrotron x-ray diffraction data confirms single phase rhombohedral crystal structure with R3c space group for all the compositions and anti-phase (a-a-a-) octahedral tilting angle decreased with increase in composition. Homogeneity and elemental proportions were confirmed by Energy dispersive x-ray spectrometry. The temperature-dependent dielectric study has shown two diffuse type of dielectric anomaly for all the samples, due to A-site disorder in the lattice, which has been assigned to two-phase transitions: ferroelectric to anti-ferroelectric and anti-ferroelectric to the paraelectric phase transition. Thermal stability range of dielectric constant increases from ~100 to 220 °C as a function of composition. Stable dielectric constant first increases from 1557 ± 10% for x = 0 compositions and highest for x = 0.06 sample with εmid ~ 2508 ± 10% of the temperature range ~180–340 °C, and after that decreases to 1608 ± 10% for x = 0.12, but remain higher than the x = 0 composition. Ferroelectric measurements have shown monotonously decreasing coercive field as a function of the composition due to decrease in the average grain size, confirmed by microstructural studies using field emission scanning electron microscope. An exponential increase in the energy storage efficiency from ~ 17% to 87% as a function of composition have also observed. These types of materials, with the high stable dielectric constant (εr) and low loss (tanδ), have a vast scope in the field of the thermally stable dielectric constant materials and energy storage applications.

Effect of potassium and magnesium codoping on the dielectric properties of BST powders

ABSTRACTK and Mg codoped BST powders were prepared by a sol-gel method, and the effect of doped concentration on the dielectric performances was studied. For comparison, pure, Mg doped and K doped BST powders were studied. XRD shows all powders reveal complete diffraction peaks and ABO3 cubic perovskite polycrystalline structures. Compared to the pure BST powder, Mg doped BST powder shows a little weaker crystallization, 5%∼15% K doped BST powders exhibit stronger crystallization, and the crystallization is getting stronger with increasing K doped concentrations from 2% to 15%. BST powder shows lattice parameter of 3.963 Å, Mg doping corresponds to 3.963 Å, 2%∼20% K doping correspond to 3.963 Å∼3.967 Å, and Mg and K codoping make lattice parameters increase from 3.967 Å to 3.974 Å. Mg2+ ion and K+ ion show acceptor doped mechanisms, Mg doping makes grains refine, and K doping makes grains grow. Pure BST powder and Mg doped BST powder show uniform grains with unclear grain boundaries, K doped BST powders can obtain uniform and dispersive grains with clear grain boundaries, but Mg and K codoping makes the uniformity and dispersity of the powders getting worse. Compared to pure BST powder, Mg doped BST powder shows smaller but more stable dielectric constant and dielectric loss, K doped powders tend to reveal larger and less stable dielectric constants and dielectric losses. Mg and K codoped BST powders show less than 35 dielectric constants, and lower than 0.02 dielectric losses. Dielectric properties are strongly dependent on the crystallization, doped mechanism and morphology. Mg doped and 2% Mg 2% K and 2% Mg 5% K codoped BST powders show low and stable dielectric constants and dielectric losses, thus can meet the requirements for tunable microwave applications and other applications.

Design of h-BN-Filled Cyanate/Epoxy Thermal Conductive Composite with Stable Dielectric Properties

The thermal conductive cyanate ester/epoxy (CE/AG80) composites with hexagonal boron nitride (h-BN) reinforced were manufactured and investigated. The low and stable dielectric constant/loss of the composites with respect to both frequency (500 Hz-100 kHz) and temperature (50-350 °C) were discussed as functions of the content of h-BN. It was found that the low and stable dielectric constant/ loss of the composites can be maintained in the whole frequency range at room temperature, and the mutations of constant/loss at the frequency of 1 kHz occurred above 280 °C for all of the samples. Moreover, a remarkable enhancement of the thermal conductivity (0.54 W/mK a 1.8-fold enhancement) was achieved with the introduction of h-BN and significantly outperformed traditional thermal conductive fillers. The significant improvements of the thermal conductivity of the composites were analyzed by the Agari’s model and the parameters of C1 and C2 were also calculated.

Energy Storage of Polyarylene Ether Nitriles at High Temperature

Polyarylene ether nitrile (PEN) was synthesized and used as film capacitors for energy storage at high temperature. Scanning electron microscopy observation indicated that the films of PEN have pinholes at nanoscales which restricted the energy storage properties of the material. The pinhole shadowing effect through which the energy storage properties of PEN were effectively improved to be 2.3 J/cm3 was observed by using the overlapped film of PEN. The high glass transition temperature (Tg) of PEN was as high as 216 °C and PEN film showed stable dielectric constant, breakdown strength and energy storage density before the Tg. The PEN films will be a potential candidate as high performance electronic storage materials used at high temperature.

Analysis of the Characteristics on Dielectric Barrier Discharges Depending on the Relative Permittivity and Frequency

Various studies are being conducted on the application of DBD (Dielectric barrier discharges). The internal dielectric has a very important characteristic on DBD, thus we analyze of the characteristics on dielectric barrier discharges depending on the relative permittivity and frequency. Through simulation, the discharge voltage was calculated based on relative permittivity and frequency of real used dielectrics (Green sheet, Down dielectric, white dielectric). We investigate that increased relative permittivity and fast frequency occur the decrease of the firing voltage. Also, we investigate the frequency dependence of the dielectric constant and dielectric loss of dielectric layers measured at a frequency region of 100Hz to 10MHz. In a condition of drive within 1MHz, with regard to the change of real and imaginary part according to frequency, it has quite stable dielectric constant in the condition of drive within 1MHz.

Design of the phthalonitrile‐based composite laminates by improving the interfacial compatibility and their enhanced properties

ABSTRACTPhthalonitrile containing benzoxazine (BA‐ph) and cyanate ester (CE) were chosen as the thermosetting matrix and the glass fiber (GF) reinforced laminates formed at low temperature were designed. The polyarylene ether nitriles containing pendent carboxyl groups (CPEN) was selected to modify the interfacial interaction between the resin matrix and GFs. Two methods of introducing CPEN were compared and the effects of CPEN on curing behaviors and properties of the composites were investigated. Results showed that with the CPEN, exothermic peaks shifted to lower temperature and curing temperatures of BA‐ph/CE decreased slightly. The mechanical and thermal properties of GF‐reinforced composites were discussed and the results indicated that the composites of modified GFs with CPEN exhibited outstanding mechanical properties, higher glass transition temperature (Tg &gt; 290 °C) than that of composites composed of CPEN mixed with BA‐ph/CE. Moreover, GF‐reinforced composites showed stable dielectric constants (3.8–4.5) and low dielectric loss (0.005–0.01), which were independent of the frequency. In sum, the various methods of the introduction of CPEN in the GF‐reinforced composites may provide a new route to prepare improved composites, meanwhile, composites with outstanding processability and excellent mechanical and thermal properties are expected to be widely applied in the fields of high‐performance structural materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45881.

Development of a capacitive sensor for concrete structure health monitoring

A novel low-cost capacitive transducer (CT) using capacitance signals, which has the potential to provide accurate health assessment and damage prediction for reinforcement concrete structures, is developed in this study. Two designs of capacitive transducers are discussed for condition assessment of rebar and concrete, respectively. Both of them consist of a supporting structure and a pair of corresponding parallel electrode plates. In order to verify the effectiveness of the designed capacitive sensor, a series of preliminary experiments are conducted. The results show that the detected CT signals rise with the increasing rebar size. Pure cement paste and fiber-reinforced concrete have demonstrated a stable dielectric constant under the same fabrication conditions. To simulate the real reinforced concrete case, various sizes of rebars were placed in fiber reinforced concrete. It is found that monitoring the CT signals is an effective way to assess the rebar diameters inside concrete. Experiments results also showed that CT signals could be applied to predict rebar positions inside the concrete. Finally, FEM simulations were implemented for the last experiment, and comparison results have well verified the effectiveness of the developed capacitive sensor. The whole work has demonstrated a promising application of the capacitive sensor in NDT of reinforced concrete in the future.

Stable Dielectric Properties in the Intermediate Temperature Range of 50°C to 260°C for Na0.5Bi0.5TiO3-SrTiO3 Ceramics with Er2O3 Doping

To meet the requirement for capacitors with low loss and stable dielectric constant in the intermediate temperature range, (1 − x)Na0.5Bi0.5TiO3–xSrTiO3 (x = 0.2, 0.3, 0.4, 0.5) ceramics have been synthesized by conventional solid-state reaction. Dielectric measurements showed double-shoulder dielectric peaks for the ceramics, with the ceramic having x = 0.3 showing the most stable behavior. Furthermore, Er2O3 was doped into the 0.7Na0.5Bi0.5TiO3–0.3SrTiO3 ceramic at content of 0.02 mol.% to 0.10 mol.%. The results show that Er doping can widen the flat temperature range and decrease the dielectric constant. The ceramic doped with 0.75 mol.% Er2O3 showed the widest temperature range of 50°C to 260°C in a dielectric constant window of <±5% around 2420 with loss <0.02. Ceramics in the 0.7Na0.5Bi0.5TiO3–0.3SrTiO3 system are therefore attractive dielectrics for use in applications at intermediate temperatures.

Experimental and simulation-based understanding of morphology controlled barium titanate nanoparticles under co-adsorption of surfactants

Well dispersed single-crystalline BaTiO3 nanoparticles with controlled morphologies were synthesized using a thermohydrolysis route. The nanoparticles were tuned from spherical to cubic upon changing the NaOH concentration under a critical molar ratio of oleic acid to hydrazine. Density functional theory (DFT) and molecular dynamics (MD) calculations indicated that hydrazine molecules adsorbed preferably on the Ti position of the Ti–O terminated surface; meanwhile, oleic acid molecules tended to adsorb on the Ba position of the Ba–O terminated surface. The added hydrazine changed the formation mechanism of BaTiO3 nanoparticles from an in situ growth to a dissolution–precipitation growth. Excellent dispersibility in aqueous solution was achieved for the BaTiO3 nanoparticles under the assistance of hydrazine. Meanwhile, a high-quality self-assembled film with a stable dielectric constant of 30 in the frequency range from 0 Hz to 1 MHz was prepared using the well dispersed BaTiO3 nanoparticles, providing a novel low-temperature route for the fabrication of perovskite films.

Investigation on the Correlation between Structural and Electrical Properties of Lanthanum Doped Barium Titanate Ceramics

The structure-property relationship of 0.3, 0.5 and 0.7mole% lanthanum (La2O3) doped Barium titanate (BaTiO3) ceramics prepared by solid state sintering under different sintering conditions were investigated in this research. The raw materials were La2O3 (grain size=~80nm) and BaTiO3 (grain size=100nm) powders. Field Emission Scanning Electron Microscope (FE-SEM) was used to examine grain size and surface morphology of sintered pellets &amp; X-Ray Diffraction analysis was conducted to identify crystal structure. The results showed significantly improved grain size and electrical properties of BaTiO3 for 0.5 mole% La2O3 with desired grain size (0.8-1.3μm), high densification (&gt;90% theoretical density) and stable dielectric constant (12700) at room temperature (f=100Hz) by lowering curie temperature around 30oC by sintering at 1300oC for 8 hrs. A gradual deterioration follows with increased doping concentration. So the research revealed that proper La3+ concentration can inhibit grain size and lower Curie temperature hence significantly improving the electrical properties of BaTiO3 ceramics.