Stable Permittivity Research Articles

SrTiO3 doped KLBBNT ceramics with wide dielectric temperature stable range and high permittivity

(1-x)K0.05La0.05Ba0.054(Bi0.5Na0.5)0.846Ti0.95Cr0.025Nb0.025O3-xSrTiO3 ceramics (abbreviated as (1-x)KLBBNT-xST, x=0.05, 0.1, 0.15, 0.2) were fabricated using solid state reaction method. The ceramic sample with x=0.05 demonstrates outstanding temperature stability of dielectric properties, achieving a maximum permittivity (εrmax) of approximately 3420. The temperature coefficient of capacitance (TCC) of x=0.05 ceramics remains within −15 %≤TCC≤15 % over the temperature range of 54–308 ℃. Analysis of the phase structure and ε-temperature graphs suggests that the outstanding dielectric temperature performance may be attributed to the multiple elements doping strategy, which improves the dielectric constant while expanding the temperature region of dielectric temperature stability. This study presents a novel approach for achieving wide dielectric temperature stable range and high permittivity in BNT-based ceramics simultaneously.

Noniterative and Stable Permittivity Extraction of Solid Dielectrics Using a New Formalism Based on Frequency-Domain and Time-Domain Analyses

Noniterative and Stable Permittivity Extraction of Solid Dielectrics Using a New Formalism Based on Frequency-Domain and Time-Domain Analyses

Broad temperature range with stable permittivity and low dielectric loss in (1–2x)Na0.5Bi0.5TiO3-xNaNbO3-xGdFeO3 system

High-temperature capacitors have garnered increasing attention in current research due to the inability of commercially available capacitors to meet the evolving industry demands. In this study, a Na0.5Bi0.5TiO3 based ternary system, denoted as [(1–2x)(Na0.5Bi0.5TiO3) -x(NaNbO3) -x(GdFeO3): x=0.01–0.09], was synthesised through solid-state reaction route. The influence of NaNbO3 and GdFeO3 on phase structure, dielectric, and ferroelectric properties are investigated. A fall of polar R3c phase % from X-ray refinement studies, diminishing macroscopic polarization, increasing breakdown strength, and flattening of temperature-dependent dielectric permittivity curves are perceived with the increase of substituent concentration. Temperature stable permittivity of (1–2x)(Na0.5Bi0.5TiO3) -x(NaNbO3) -x(GdFeO3) calculated ε'r/ε'r [250℃] at 1, 10, 100, 500 kHz with 10 % tolerance. Remarkably, (Δε′/ε′250°C ≤ ± 10 %) with x = 0.07 and 0.09 showed stable permittivity in the wide temperature range of (30°C to 600°C) at 500 kHz and a minimal dielectric loss (tan δ ≤ 0.01) measured at 250°C makes it a promising candidate for high-temperature dielectric capacitor applications.

Unleashing the potential of a new Y–BaTiO3/graphene oxide nanocomposites for boosting the dielectric stability at high temperature

This report presents a novel dielectric study of Ba1-xYxTi(1-x/4)O3 (x = 0, 2 %, 4 %, 6 %, and 8 %) with graphene oxide (GO) via sonication. BaTiO3 (BT) is a well-known ceramic material with excellent properties, and its temperature stability is crucial for high-temperature applications. However, there is a lack of scientific research exploring this stability at elevated temperatures. This research provides valuable insights into the stability of BaTiO3-Yttrium-based ceramics, particularly in conjunction with graphene (BYT@GO), paving the way for potential applications in high-temperature environments. The tetragonality of the structures was identified by powder X-ray diffraction. A uniform grain size was observed for BT@GO, However, BYT@GO (Y% = 2 %, 4 %, 6 %, and 8 %) exhibited a homogeneous morphology and dense microstructure, as observed by scanning electron microscopy. Dielectric measurements were conducted to evaluate the permittivity of the materials as a function of frequency at room temperature. All ceramics demonstrated stable permittivity and low dielectric losses as a function of frequency (<2 × 10−4 for BT@GO, 4 × 10−3 for BYT4%@GO, 6 × 10−3 for BYT6%@GO, and 8 × 10−3 for BYT8%@GO). In addition, BT@GO and BYT 8 %@GO exhibited exceptional dielectric stability at temperatures ranging from 20 to 300 °C.

Design of miniaturized and high gain dielectric lens antenna

AbstractA miniaturized and high‐gain dielectric lens antenna is presented and demonstrated. The dielectric lens antenna is mainly composed of a spherical dielectric lens, a pedestal, and a radiating element. The spherical dielectric lens is made of a special material called cross‐linked styrene co‐polymer showing an ultra‐low dielectric loss and a stable permittivity. The pedestal is made by the 3D printing technique and used for supporting the dielectric lens. The radiating element is embedded in the bottom of the pedestal, a proper spacing between the dielectric lens and the radiating element is maintained. The proposed dielectric lens antenna shows impedance bandwidth ranging from 24.4 to 25.8 GHz and an excellent directional radiation characteristic is obtained.

AlN high temperature co-fired ceramics with enhanced frequency selective transmission from X to Ku bands at elevated temperature

Syncretism of the functional structure and high temperature (HT) resistant ceramic are investigated to realize frequency selective transmission of device under HT environment. Focused on the electromagnetic (EM) properties of materials, metal tungsten with high-melting-point and ceramic AlN with stable permittivity under 1000 ℃ are selected as the functional structure and substrate of the proposed HT transmitter, respectively. To make the desired transmission, meta-structure is utilized into the design of W structure, which is designed inside AlN ceramic for metal’s conductivity protection. In terms of fabrication, the transmitter is manufactured by high temperature co-fired technique. Through stacking sheets, lamination, and co-fired, the metal structure is processed in the sealed interlayer to prevent oxidation. As demonstrations, single- and double- layer transmitters are designed to satisfy single and double passband from X to Ku bands, respectively. The success of proposed design manner profoundly increases the design freedom for HT EM manipulation, and we firmly believe that the proposed design-fabrication method has great application potential in future EM devices in extreme environments.

Enhanced energy storage efficiency and temperature stability of Li2CO3-assisted BST-based ceramics by optimizing B-site dopants

In this work, 5 wt‰ Li2CO3-doped 0.88Ba0.8Sr0.2TiO3-0.12BiMeO3 (BST-BMe+5‰Li2CO3, Me = Al3+, Ga3+, Ta5+, and In3+) ceramics were fabricated using solid phase sintering approach. The impacts of different B-site Me ions on the crystalline structure, permittivity stability, energy density, and energy storage efficiency of these ceramics were studied. The XRD results revealed that the mixed tetragonal (T) and pseudo cubic (pC) phase structure was obtained for all the samples. The In/5‰Li2CO3 sample exhibits the optimal energy density of Wrec = 1.04 J/cm3 and the energy efficiency of η = 96% at 170 kV/cm. Meanwhile, the sample shows outstanding temperature stability satisfying the EIA-X8R criteria, which is ascribed to the combined roles of defect dipoles and large lattice distortion. Li2CO3 plays a key role in reducing the sintering temperature, raising the breakdown strength, enhancing the relaxation characteristics, and improving the thermal stability of energy efficiency of the ceramics.

TeO2: A Prospective High‐k Dielectric

Herein, high‐k dielectric behavior of TeO2 thin films is investigated. The films are prepared using pulsed laser deposition on indium tin oxide (ITO)–glass substrates. Increasing the growth temperature has improved the surface roughness, transparency, and bandgap of the films. Films grown at 500 °C display nanocrystalline nature which is reflected in the increase of bandgap to 4.7 eV and is higher than the bulk value of α‐TeO2 (3.7 eV). The nanocrystalline TeO2 films in the metal–insulator–metal configuration show a stable high permittivity of ≈19 with low leakage current (J &lt; 1 × 10−7 A cm−2) and good voltage stability (α = 509 ppm V−2). Field‐effect modulation is observed in the metal–oxide–semiconductor stack configuration with tellurium as a semiconductor. The study suggests nanocrystalline TeO2 as a low‐temperature processable high‐k material with high transparency for transistor applications.

Investigation of Structural and Electrical Properties of Al2O3/Al Composites Prepared by Aerosol Co-Deposition

As the microelectronic industry develops, components that can perform several different tasks receive increasingly more attention, resulting in multifunctional materials being highly sought after. Al2O3 is widely present in electronic applications as a protective coating or as an electrical and thermal insulator due to its mechanical and thermal stabilities and chemical inertness. Al2O3 is also an important dielectric material, with high resistivity and stable permittivity over a wide range of temperatures and electric fields, but its modest permittivity necessitates large effective areas or extremely thin layers when a large capacitance is desired. Composites consisting of discrete conducting phases within an insulating matrix can produce large capacitance via Maxwell–Wagner polarization. In this work, Al2O3/Al composite thick films with different volume ratios of Al were prepared using the aerosol deposition method. A relative dielectric permittivity (εr′) of 800 at 1 MHz was achieved at 27 vol% of Al, a sixty-sevenfold enhancement compared to Al2O3. On the other hand, dielectric losses, tan(δ), at 1 MHz increased from 0.01 for Al2O3 up to 0.58 for the composite with 27 vol% of Al. A finite-element model of the composites was implemented, supporting the nonlinear electrical behavior of the composites as function of vol% of Al. Our results show novel possibilities for the applications of Al2O3-based materials in the microelectronic industry, especially for temperature-sensitive applications, for which the integration strengths of aerosol deposition are valuable.

Dielectric measurement by open-ended coaxial line for hot-mix asphalt roads: From laboratory test to on-site investigation

Dielectric permittivity of road material is an important parameter to calculate the velocity of electromagnetic waves when evaluating the geometry of pavements by ground penetrating radar (GPR). Conventional methods need to prepare core samples for the measurement, which is not convenient nor representative. In this work, we present a non-destructive open-ended coaxial probe to measure the frequency-dependent dielectric permittivity and the results include laboratory tests and on-site investigation. In the laboratory part, we test the slab samples and compare the results with a validated test (coaxial/cylindrical transition line). Due to the limited size, the dielectric results obtained by the open-ended probe are a bit lower than those by the validated test. However, the thickness problem can be ameliorated in the on-site investigation because of the infinitive scale of the road. In the on-site part, the tested dielectric constant of the road can well agree with the calculated value by the Maxwell-Garnett law based on the volumetric fractions of the bitumen, aggregates, and air. Moreover, the stable dielectric permittivity in the tested frequency by open-ended probe can be used to fit the dielectric constant at higher frequency by Debye model. This can provide a dielectric constant at high frequency for estimating the geometry of the multi-layered structure in the surface course. The estimated results are close to the tested lengths of core samples.

Structure and dielectric properties of yttrium-doped Ca0.28Ba0.72Nb2O6 ceramics

An unfilled tungsten bronze-structured ferroelectric ceramic, Ca0.28Ba0.72Nb2O6 (CBN28), has been doped with Y3+ to produce ceramics with a nominal composition, (Ca0.28Ba0.72)1–3w/2YwNb2O6 [0 ≤ w ≤ 0.05]. The substitution of Y3+ for Ca2+/Ba2+, and consequent additional vacancy formation, is assumed to occur on the A1/A2 sites. This resulted in a minor reduction of the c lattice parameter, and unit cell volume. For undoped CBN28, there was a slightly diffuse relative permittivity-temperature (εr-T) peak at 268 ⁰C. The peak became much broader for sample compositions w = 0.04 and 0.05 and the peak temperature showed a level of frequency dependence consistent with weak relaxor behaviour. The polarisation-electric field loops became narrower for samples w = 0.04 and 0.05, corresponding to a reduction in remnant polarisation value, from 2.4 to 0.8 µC cm−2 (30 kV cm−1). The Y doped ceramics exhibited stable relative permittivity over a wide temperature range, the variation being within± 15% of the median value from 36 ⁰C to 218 ⁰C for w = 0.05, when measured at 1 kHz. Consequently, we suggest that A site donor-doping and aliovalent B site doping of CBN holds potential for industry standard, temperature stable, high temperature dielectrics (ɛr ≥ 500 ± 15% from - 55–250 + ⁰C).

Large permittivity, low loss and defect structure in (Nb, Zn) co-doped SnO2 ceramics studied through a combined experimental and DFT calculational method

Dielectric ceramics with high permittivity and low loss are widely used in electronic components and devices. In this study, (Nb, Zn) co-doped NbxZnySn1-x-yO2 with different doping levels and Nb/Zn ratios was designed to tune the defect structure toward the optimal dielectric performance. The lattice parameters firstly increased from x = y = 0.01 to 0.03 and then decreased, while the oxygen vacancy concentration decreased with doping. The co-doped sample with x = y = 0.02 exhibits stable permittivity up to 800 with an ultra-low loss tanδ ∼0.03 at 40 Hz. DFT calculation showed that the oxygen vacancy was formed with single-Zn doping and co-doping at low doping level, while the hole was generated at higher doping level. The achieved large permittivity and low loss of the sample are related to both Electron-Pinned Defect Dipoles (EPDD) and Hole-Pinned Defect Dipoles (HPDD) effects in the lattice, which was determined by the relative positions of donor and acceptor dopants.

Ultra-low temperature cofired ceramics based on Li2WO4as perspective substrate materials for terahertz frequencies

With the development of low dielectric permittivity materials having an ultra-low sintering temperature, testing their dielectric properties at terahertz frequencies suitable for 6G communication systems and implementation of the fabricated materials in ultra-low temperature cofired ceramics (ULTCC) were the main goals of the research. Lithium tungstate Li₂WO₄ was synthesized by a solid-state reaction and used for the preparation of green tapes and test structures with cofired internal conductive layers, which are destined for substrates of microwave and submillimeter wave circuits. Sintering behavior, thermal effects, and mass changes of the green tapes during heating were studied using a hot-stage microscope, differential thermal analysis, and thermogravimetry. A single-phase composition was revealed for being undoped and doped with AlF₃–CaB₄O₇ ceramics. The impact of frequency, temperature, the addition of AlF₃–CaB₄O₇ and CuBi₂O₄ dopants, and sintering temperature was the subject of in-depth characterization of dielectric properties in a terahertz region. A glass-free composition, ultra-low sintering temperature of 590–630 ℃, low roughness of the green tapes, dense microstructure, compatibility with Ag conductors, low and stable dielectric permittivity of 5.0–5.8 in a broad range of 0.2–2 THz, and low dielectric loss of 0.008–0.01 at 1 THz are the main advantages of the developed ULTCC substrates.

Super-stable permittivity and low dielectric loss of (1-x)Na0.5Bi0.5+yTiO3-xNaTaO3 ceramics within an ultra-wide temperature range

This work designs a new system (1-x)Na0.5Bi0.5+yTiO3-xNaTaO3 with a nonstoichiometric bismuth ratio, which is used as dielectrics of ceramics capacitors. Phase structure evolution of (1-x)Na0.5Bi0.5+yTiO3-xNaTaO3 is characterized using XRD, Raman and TEM. Dielectric and resistant properties of (1-x)Na0.5Bi0.5+yTiO3-xNaTaO3 are investigated with increasing concentration of NaTaO3. With these investigations, the structure and defect chemistry of (1-x)Na0.5Bi0.5+yTiO3-xNaTaO3 are rationalized and their respective impact on capacitor properties are elucidated. The optimized composition 0.8Na0.5Bi0.51TiO3-0.2NaTaO3 possesses an ultra-wide operating temperature range (-92–398 °C), in which both stable permittivity and low dielectric loss is obtained. Furthermore, the fabrication of multilayer ceramics capacitors (MLCC) based on 0.8Na0.5Bi0.51TiO3-0.2NaTaO3 dielectrics is investigated. With the addition of sintering aids, 0.8Na0.5Bi0.51TiO3-0.2NaTaO3 could be co-fired with Ag at 910 °C in air, and the low temperature co-fired ceramic (LTCC) capacitors maintain good temperature stability of permittivity and low dielectric loss in -100–352 °C. Therefore, our work provides a new route for preparing ultra-wide operating temperature capacitors at low manufacturing costs.

Decoupling of Dual-Polarized Antenna Arrays Using Non-Resonant Metasurface.

A non-resonant metasurface (NRMS) concept is reported in this paper to improve the isolation of dual-polarized and wideband large-scale antenna arrays. By properly designing the NRMS, it can perform stable negative permeability and positive permittivity along the tangential direction of the NRMS within a wide band, which can be fully employed to suppress the mutual couplings of large-scale antenna arrays. At the same time, the proposed NRMS can also result in positive permittivity and permeability along the normal direction of the NRMS, which guarantees the free propagation of electromagnetic waves from antenna arrays along the normal direction. For demonstration, a 4×4 dual-polarized antenna array loading with the proposed NRMS is designed to improve the isolations of the antenna array. The simulations demonstrate that the isolations among all ports are over 24 dB from 4.36 to 4.94 GHz, which are experimentally verified by the measured results. Moreover, the radiation patterns of antenna elements are still maintained after leveraging the proposed NRMS. Due to the simple structure of the proposed NRMS, it is very promising to be widely employed for massive MIMO antenna arrays.

Antiferroelectric-like Behavior in a Lead-Free Perovskite Layered Structure Ceramic.

Antiferroelectric (AFE) materials have been intensively studied due to their potential uses in energy storage applications and energy conversion. These materials are characterized by double polarization-electric field (P-E) hysteresis loops and nonpolar crystal structures. Unusually, in the present work, Sr1.68La0.32Ta1.68Ti0.32O7 (STLT32), Sr1.64La0.36Ta1.64Ti0.36O7 (STLT36), and Sr1.85Ca0.15Ta2O7 (SCT15), lead-free perovskite layered structure (PLS) materials, are shown to exhibit AFE-like double P-E hysteresis loops despite maintaining a polar crystal structure. The double hysteresis loops are present over wide ranges of electric field and temperature. While neutron diffraction and piezoresponse force microscopy results indicate that the STLT32 system should be ferroelectric at room temperature, the observed AFE-like electrical behavior suggests that the electrical response is dominated by a weakly polar phase with a field-induced transition to a more strongly polar phase. Variable-temperature dielectric measurements suggest the presence of two-phase transitions in STLT32 at ca. 250 and 750 °C. The latter transition is confirmed by thermal analysis and is accompanied by structural changes in the layers, such as in the degree of octahedral tilting and changes in the perovskite block width and interlayer gap, associated with a change from non-centrosymmetric to centrosymmetric structures. The lower-temperature transition is more diffuse in nature but is evidenced by subtle changes in the lattice parameters. The dielectric properties of an STLT32 ceramic at microwave frequencies was measured using a coplanar waveguide transmission line and revealed stable permittivity from 1 kHz up to 20 GHz with low dielectric loss. This work represents the first observation of its kind in a PLS-type material.

Role of polyaniline coating on nanosilica particles in polyvinylidene fluoride nanocomposites for energy storage

Polymer nanocomposites, which are characterized by a high dielectric permittivity, are intensively studied for microelectronic devices and energy storage applications. Poly(vinylidene fluoride) (PVDF) has a higher dielectric permittivity among polymers, is flexible, lightweight and easy to be processed. One route to enhance its mechanical and dielectric properties is the addition of inorganic nanofillers. Therefore, PVDF was melt compounded with nanosilica in various proportions, from 5 to 30 wt%. For enhancing the stored and released electric energy densities, polyaniline (PANI) was obtained in situ on the surface of nanosilica in both acid and basic media; further the nanosilica particles coated with PANI were incorporated in PVDF by melt compounding to improve the dielectric properties by adding new interfaces. The addition of nanosilica in PVDF led to a strong increase in its storage modulus without reducing its good thermal stability. Moreover, an important increase in PVDF permittivity was determined by increasing content of nanosilica in nanocomposites. PANI coating influenced both thermal and mechanical properties and led to nanocomposites with more stable dielectric permittivity and lower dielectric loss than neat PVDF at frequencies between tens Hz and tens kHz, which is very important for energy storage applications.

Anisotropic dislocation-domain wall interactions in ferroelectrics

Dislocations are usually expected to degrade electrical, thermal and optical functionality and to tune mechanical properties of materials. Here, we demonstrate a general framework for the control of dislocation–domain wall interactions in ferroics, employing an imprinted dislocation network. Anisotropic dielectric and electromechanical properties are engineered in barium titanate crystals via well-controlled line-plane relationships, culminating in extraordinary and stable large-signal dielectric permittivity (≈23100) and piezoelectric coefficient (≈2470 pm V–1). In contrast, a related increase in properties utilizing point-plane relation prompts a dramatic cyclic degradation. Observed dielectric and piezoelectric properties are rationalized using transmission electron microscopy and time- and cycle-dependent nuclear magnetic resonance paired with X-ray diffraction. Succinct mechanistic understanding is provided by phase-field simulations and driving force calculations of the described dislocation–domain wall interactions. Our 1D-2D defect approach offers a fertile ground for tailoring functionality in a wide range of functional material systems.

Transition of the colossal permittivity related dielectric relaxation in V-doped CaCu3Ti4O12 ceramics

The co-achieving of stable colossal permittivity (CP) and low dielectric loss in dielectric materials has been a challenge. In this paper, a transition in CP was observed in V-doped CaCu3Ti4O12 (CCTO) ceramics. The fast high-frequency dielectric relaxation that mainly contributed to CP of CCTO ceramics was greatly suppressed in V-doped CCTO samples. Its relaxation activation energy remained ∼0.10 eV, while its magnitude dropped from thousands in CCTO to dozens in V-doped CCTO. Instead, CP of V-doped CCTO ceramics mainly arose from another slow dielectric relaxation, which appeared in a much lower frequency range. Moreover, this dielectric relaxation gradually turned from a “carrier-dominated” relaxation into a “dipole-dominated” one with the increase in temperature. Its relaxation activation energy also changed from ∼0.06 to 0.42 eV in the meanwhile. These results indicated important roles of multiple point defects and their relating charge transport in CP behaviors. It supported that CP arose from electron trapping behaviors at the edge of double Schottky barriers at grain boundaries. On this basis, suppression of any deep-level point defects was concluded to be a potential clue to achieve both stable CP and sufficiently low dielectric loss in CCTO ceramics and other CP materials.

Effect of Na/K ratio on structure evolution, dielectric and energy storage properties of potassium sodium niobate-based borate glass-ceramics

To reduce carrier mobility and optimize crystal phase species, 0.9((1-x)K2O-xNa2O-Nb2O5)-0.1B2O3 glass-ceramics were prepared by the traditional melting method. By introducing Na2O, Na0.9K0.1NbO3 ferroelectric phase increases, and the “rice-like” morphology grains transfer to the cubic grains gradually. As the radius of Na+ is smaller than K+, the ability of Na+ to provide free oxygen is weaker, which reduces the fracture degree of [BO3] and makes the glass network structure tend to compact. As a result, the stable high permittivity (158) and low dielectric loss (tanδ ≤ 0.04) are obtained in the broad frequency range (20 Hz to 1 MHz) and temperature range (25–200 °C). In addition, these samples also reveal a relatively high energy-storage density (1.64 J/cm3) under breakdown strength (490 kV/cm), which is mainly attributed to the dense glass network and optimized crystalline phase. Pulse discharge testing further verifies that the 0.9(0.5K2O-0.5Na2O-Nb2O5)-0.1B2O3 glass-ceramic achieves high actual energy-storage density (0.09 J/cm3) at lower electric field strengths, and fast charging and discharging speed (τ0.9 = 15 ns).