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The type of multi-component fillers and their spatial distribution in conductive polymer-based composites greatly influenced their electrical properties, electromagnetic shielding efficiency (SE), and absorption capability, which require a deep understanding of how these properties improve with changes in the phase composition, content, and distribution of these fillers in the composite. In this study, three-phase polymer composite materials (CMs) with random (epoxy-based) and segregated (polyethylene-based) distribution of nanocarbon (graphite nanoplatelets GNP and carbon nanotubes CNTs) and magnetic (Fe and Co3O4) fillers have been developed. It was found that permittivity ε r ′ in the frequency range (40–60 GHz) increases sufficiently with the nanocarbon content and their values are slightly higher for random GNP-filled CMs (ε r ′ = 10 – 15 for 3–5 wt. % GNP) compared to CNT-filled CMs and much higher compared to segregated CMs (ε r ′ = 4 – 7 for 3–5 wt. % of nanocarbon). Dielectric loss tangent tan δ is increased with the nanocarbon content (especially for Fe-filled CMs) and sufficiently higher in segregated CMs compared to similar random composites. These enhanced tan δ values correlate with higher electromagnetic shielding efficiency due to absorption of segregated nanocarbon/magnetic/polyethylene CMs, for example, SEAd ≈ 18–23 dB/mm for 5 wt. %GNP. The most preferable for microwave absorption are random and segregated CMs with 2–3 wt. % GNP/30 wt. % magnetic filler: RLmin = −(27–35) dB, effective absorption bandwidth (EAB) Δ f 10 dB = 11.5 – 12.5 GHz at a sample thickness of 0.5–0.7 mm. In CNT-based segregated CMs, | R L min | and EAB values are lower compared with GNP-based CMs. The ability to manipulate these characteristics is important for obtaining good shielding and absorptive properties in the microwave range of electromagnetic radiation. [ABSTRACT FROM AUTHOR]

Epoxy dielectrics with high through-plane thermal conductivity (λ) hold great promise for applications in the thermal management of advanced power electronics. Intensive attempts have been made to improve the λ of epoxy by filling with boron nitride nanosheets (BNNSs). However, it remains a great challenge to achieve a satisfactory increased λ by a small amount of BNNS loading. Herein, we reported a new strategy to prepare epoxy dielectrics with internal three-dimensional phonon transport channels by vacuum freeze-drying and vacuum impregnation. Aramid nanofibers (ANFs) and BNNSs were used for the collaborative construction of a vertical interconnected thermal framework. The resultant ANF-BNNS/epoxy achieved a high through-plane λ of 0.87 W m−1 K−1 at only 1.43 vol. % BNNS, which is ∼17.1% higher than that of the BNNS/epoxy counterpart with even 18.34 vol. % randomly distributed BNNS. The increasing efficiency of λ of epoxy by ANF-BNNS is tenfold more than that of the conventional blending methods. In addition, the ANF-BNNS/epoxy composite also exhibits a low dielectric constant and low dielectric loss. The findings of this study offer an inspired venue to develop high-performance thermally conductive epoxy dielectrics with a minimal BNNS loading. [ABSTRACT FROM AUTHOR]

In a class of high quality (Q-) factor dielectric resonators with low radiative losses, including popular whispering-gallery mode (WGM) resonators with high azimuthal mode numbers, due to high confinement of modal field in dielectric, the Q-factor is limited by the value of inverse dielectric loss tangent of dielectric material. Metal enclosures necessary for device integration only marginally affect the Q-factor while eliminating the residual radiative loss and allowing the optimization of input and output coupling. While very high Q-factors ∼ 200 000 are available in sapphire WGM resonators in X-band, at millimeter wave frequencies increasing dielectric loss limits the Q-factor to much smaller values, e.g. ∼50000 and ∼25000 for quasi-TE and quasi-TM modes, correspondingly, at 36 GHz. The use of distributed Bragg reflection (DBR) principle allows to push modal energy outside dielectric while also isolating it from Joule losses in metallic enclosure walls. Very high Q ∼ 600 000 > --> t g δ has been demonstrated in X-band [C. A. Flory and R. C. Taber, IEEE Trans. Ultrason., Ferroelectr., Freq. Control 44, 486–495 (1997).] at the expense of impractically large dimensions. In this work, we report on the assembly and testing of a compact Ka-band sapphire distributed Bragg reflector cavity characterized with Q-factor seven times larger than one predicted by the material's dielectric loss at the frequency of interest. An intrinsic Q-factor of ∼ 200 000 is demonstrated at 36 GHz for the lowest order TM-mode of a sapphire DBR. The resonator has 50 cm 3 volume, smaller than previously demonstrated DBRs. [ABSTRACT FROM AUTHOR]

The microstructure morphology, static magnetic properties, and electromagnetic absorption characteristics of nano FexCoNi alloy particles prepared by chemical liquid deposition with five different Fe content levels are investigated in this paper. The results show that spherical FexCoNi alloy particles with an average particle size of about 100–200 nm and a face-centered cubic crystal structure were obtained. All five samples exhibited soft magnetic behavior, with the saturation magnetization intensity showing an increasing-then-decreasing trend with increasing Fe content, peaking at 141.8 emu/g for Fe content x = 1.0. The dielectric constants (real and imaginary parts) of the prepared alloy particles exhibit significant differences with respect to the variation of Fe content, while the changes in the real and imaginary parts of the magnetic permeability show less pronounced effects with increasing Fe content. As the electromagnetic wave frequency increases, the real parts of the dielectric constants for all composites show minimal fluctuations, and the real parts of the magnetic permeability exhibit a decreasing trend. Moreover, the imaginary parts of the dielectric constants and magnetic permeability show an increasing followed by a decreasing trend as the frequency rises. The material with Fe content x = 1 demonstrated optimal dielectric loss performance and relatively excellent magnetic loss performance, with a sample thickness of 1.9 mm exhibiting the highest reflection loss (RLmax) of −24.2 dB and an effective absorption bandwidth of 4.48 GHz. [ABSTRACT FROM AUTHOR]

Measurement of high-temperature physical properties at microwave frequency is important to interpret the heating behavior of NiO observed in the author's previous studies. In this study, the impedance (4 Hz–5 MHz) and permittivity [at the microwave frequency (2.45 GHz)] of NiO powder particles were measured from room temperature (RT) to 800 °C. At high frequency above 100 kHz, the conductivity is almost independent of temperature up to a certain temperature (Ti). Above Ti, the conductivity showed a strong positive dependence on the temperature. In this region, the apparent activation energy is determined to be 0.51 eV, which is close to that of the previously reported large polaron transport mechanism (band-like conduction). It was also shown that the conductivity increased linearly with frequency and that a dielectric conductivity relation (σ = ωε″) holds, which is different from the hopping mechanism of the small polaron. Considering these results, it was understood that the temperature increase occurred preferentially in the microwave E-field. The slow increase from the room temperature is due to a small but finite dielectric loss at room temperature, and because of the low conductivity, induction current is not effectively generated in the H-field. On the other hand, after a certain time, the temperature rises to reach the large temperature-dependent conductivity, and then, a significant temperature rise occurs. [ABSTRACT FROM AUTHOR]

Glassy films of methyl-m-toluate have been vapor deposited onto a substrate equipped with interdigitated electrodes, facilitating in situ dielectric relaxation measurements during and after deposition. Samples of 200 nm thickness have been deposited at rates of 0.1 nm/s at a variety of deposition temperatures between 40 K and Tg = 170 K. With increasing depth below the surface, the dielectric loss changes gradually from a value reflecting a mobile surface layer to that of the kinetically stable glass. The thickness of this more mobile layer varies from below 1 to beyond 10 nm as the deposition temperature is increased, and its average fictive temperature is near Tg for all deposition temperatures. Judged by the dielectric loss, the liquid-like portion of the surface layer exceeds a thickness of 1 nm only for deposition temperatures above 0.8Tg, where near-equilibrium glassy states are obtained. After deposition, the dielectric loss of the material positioned about 5–30 nm below the surface decreases for thousands of seconds of annealing time, whereas the bulk of the film remains unchanged. [ABSTRACT FROM AUTHOR]

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 SiO 2 -based metal-oxide semiconductor field-effect transistor devices. RCrO 3 (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 ′ ∼ 10 4) in RCrO 3 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 DyCrO 3 , 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 DyCrO 3 (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 (TC ϵ) ∼ 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. [ABSTRACT FROM AUTHOR]

A phase-separated borosilicate glass, with a relative permittivity ranging from 3 to 3.5 and a loss tangent as low as 5.6 × 10−4, is presented for packaging applications for the next generation of mobile communications. Ionic polarizability for each borosilicate composition was calculated from the Clausius–Mossotti relationship for both the vitreous and crystalline structures, and the polarizability difference between the two is proportional to the dielectric loss. Small amounts of alkali modifier were added to improve the glass processability, and the loss tangent increased to the 1–7 × 10−3 range. The resulting glass is phase-separated, which has no impact in the millimeter-wave spectrum, as the wavelengths are considerably greater than the length scale of each immiscible phase. [ABSTRACT FROM AUTHOR]

The dielectric properties of the carbon nanotubes (CNT) doped nematic liquid crystal (NLC) are studied theoretically. The temperature and frequency dependence of the real and imaginary part of the complex dielectric permittivity and dielectric loss factor of the CNT doped NLC are calculated. The effects of CNT on the real and imaginary part of dielectric permittivities are discussed by comparing with experimental results. An appreciable change in the dielectric permittivity has been observed in the CNT doped NLC. [ABSTRACT FROM AUTHOR]

The physical aging of supercooled glycerol induced by upward temperature steps of amplitude reaching 45 K was studied by a new method consisting in heating a micrometer-thick liquid film at a rate of up to 60 000 K/s, holding it at a constant high temperature for a controlled duration before letting it quickly cool down to the initial temperature. By monitoring the final slow relaxation of the dielectric loss, we were able to obtain quantitative information on the liquid response to the initial upward step. The so-called TNM (Tool–Narayanaswamy–Moynihan) formalism provided a good description of our observations despite the large distance from equilibrium, provided that different values of the nonlinearity parameter were used for the cooling phase and for the (much further from equilibrium) heating phase. In this form, it allowed to precisely quantify how to design an ideal temperature step, i.e., where no relaxation occurs during the heating phase. It helped bringing a clear physical understanding of how the (kilosecond long) final relaxation is related to the (millisecond long) liquid response to the upward step. Finally, it made possible the reconstruction of the fictive temperature evolution immediately following a step, evidencing the highly non-linear character of the liquid response to such large amplitude temperature steps. This work illustrates both the strengths and limitations of the TNM approach. This new experimental device offers a promising tool to study far-from-equilibrium supercooled liquids through their dielectric response. [ABSTRACT FROM AUTHOR]

The microwave (MW) dielectric permittivity of gallium oxide (β-Ga2O3) fundamentally determines its interaction with an electromagnetic wave in bulk power. Yet, there is a lack of experimental data due to limitations of high-temperature MW dielectric measurements and the large uncertainty under variable-temperature conditions. Herein, we develop a deep potential (DP) based on density functional theory (DFT) results and apply deep potential molecular dynamics (DPMD) for accurately predicting temperature-dependent MW dielectric permittivity of β-Ga2O3. The predicted energies and forces by DP demonstrate excellent agreement with DFT results, and DPMD successfully simulates systems up to 1280 atoms with quantum precision over nanosecond scales. Overall, the real part of the MW dielectric permittivity decreases with rising frequency, but the dielectric loss increases. The MW dielectric permittivity gradually increases as the temperature increases, which is closely related to the reduced dielectric relaxation time and increased static and high-frequency dielectric constants. Besides, the oxygen vacancy defects significantly reduce the relaxation time; however, augmenting the defect concentration will cause a slight rise in relaxation time. The electron localization function analysis reveals that more free electrons and low localization of electrons produced by high defect concentrations facilitate the increased relaxation time. This study provides an alternative route to investigate the temperature-dependent MW permittivity of β-Ga2O3, which attains prime importance for its potential applications in RF and power electronics. [ABSTRACT FROM AUTHOR]

In modern electronics and power systems, good-performance dielectric capacitors have an essential function. Polymer-based dielectrics are widely used in the field of dielectric capacitors because of their large dielectric constant, flexibility, low density, and ease of processing. At present, ferroelectric polymers suffer from low breakdown field strength and high dielectric losses. How to improve the performance of dielectric materials in capacitors is still a promising research. This paper chooses the ferroelectric polymer poly(vinylidene fluoride) (PVDF) that worked as the matrix, and the linear polymers polyimide, cyanoethyl pullulan (CR-S), polyethersulfone, and cyanoethylated cellulose served as fillers. This all-organic dielectric composite produced as films working in electrostatic energy storage devices is prepared by using a casting method. Analyzing the test results, the composite film exhibited excellent electrical properties when the CR-S doping content was 5 wt. %. The organic composite dielectric based on CR-S/PVDF has a breakdown field strength of 450 MV/m, a discharge energy storage density (Ue) of 10.3 J/cm3, a high dielectric constant of 10.9, and a low dielectric loss of 0.004 at 1 kHz, which is a significant improvement compared with other dielectric composites. This all-organic dielectric composite strategy offers a new approach to achieve better-performance dielectric energy storage materials. [ABSTRACT FROM AUTHOR]

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

Spinodal decomposition (SD) was incorporated into Nb-doped metastable TiO2–SnO2 to achieve giant interfacial polarization. The dielectric characteristics were analyzed using an equivalent circuit involving electron migration, where the SD bulk is given by the universal dielectric response relation. Both the Nb–TiO2 and the Nb–SnO2 layers showed semiconductive behaviors. With increasing SD treatment temperature, the SD volume fraction increased, as did cation interdiffusion at the SD interface, resulting in a large dielectric loss. The optimal SD temperature was determined as 1100 °C, where the Maxwell–Wagner capacitance showed a very high value of 44.6 μF corresponding to the permittivity at the lowest frequency exceeding 106. Such colossal polarization was considered due to an accumulation of trapped electrons at the Schottky barrier at SD layers with different conductivities. [ABSTRACT FROM AUTHOR]

Large-size Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) based ferroelectric single crystals have been grown successfully by the vertical Bridgman method for application in the field of high-end piezoelectric devices. The piezoelectric and dielectric performance uniformity of PMN-PT based ferroelectric crystals is a critical application requirement. Recently, alternating current poling (ACP) has attracted much attention due to its low cost and high efficiency in improving the piezoelectric properties of PMN-PT based crystals. Here, we report the comparison of the performance fluctuation of direct current poling (DCP) and ACP Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ferroelectric single crystals grown in the [110] direction using the vertical Bridgman method. The fluctuation of piezoelectric coefficient d33, dielectric constant ɛT33/ɛ0, and dielectric loss tanδ was presented. We found that the average d33 and ɛT33/ɛ0 of ACP samples are 1290 and 1500 pC/N and 3890 and 4290 for two different wafers, which were 18% and 23%, 21% and 26% higher than DCP samples. The tanδ of ACP samples was much lower than that of DCP samples. The DCP and ACP samples exhibited the close data of the fluctuation ratios of d33 and ɛT33/ɛ0. The fluctuation ratios of d33 and ɛT33/ɛ0 for DCP and ACP samples are all less than 10%. This work offers a reference for practical ACP technique applications. [ABSTRACT FROM AUTHOR]

Tow-level system (TLS) loss in amorphous dielectric materials has been intensively studied at millikelvin temperatures due to its impact on superconducting qubit devices and incoherent detectors. However, the significance of TLS loss in superconducting transmission lines at liquid helium temperatures remains unclear. This study investigates TLS loss in amorphous SiO 2 at liquid helium temperatures (about 4 K) within a frequency range of 130–170 GHz, using niobium microstrip and coplanar waveguide resonators. Our results demonstrate notable power and temperature dependence of dielectric loss, with the dielectric loss and quasiparticle loss exchanging dominance at around 4 K. These findings are consistent with TLS models and provide crucial insight for the design of superconducting devices operating at liquid helium temperatures. [ABSTRACT FROM AUTHOR]

We report on temperature-dependent dielectric behavior of disordered ternary A6B2O17 (A = Zr, Hf; B = Nb, Ta)-form oxides in the GHz frequency range. The microwave dielectric properties including relative permittivity, dielectric loss, and temperature-dependent relative permittivity were characterized using cylindrical dielectric resonators using a resonant post measurement technique. Dielectric measurements through the resonant post method approach generally agree with dielectric measurements of A6B2O17 bulk ceramics measured through standard resonant post techniques. Coefficients describing the temperature-dependent relative permittivity for ternary A6B2O17 phases are strongly positive, suggesting contributions to polarizability arising from long-range mechanisms potentially associated with structural disorder. These observations support the working hypothesis that material functionality can be engineered by the chemical diversity and structural disorder possible in high configurational entropy A6B2O17 phases. [ABSTRACT FROM AUTHOR]

Electric field dependent capacitance and dielectric loss in poly(3-hexylthiophene) are measured by precision capacitance bridge. Carrier mobility and density are estimated from fits to current–voltage and capacitance data. The capacitance varies largely at lower frequency, and it decreases at higher electric fields. The negative capacitance at low frequency and high field is due to the negative phase angle between the dipole field and the ac signal. The intrinsic carrier density is calculated from fits to the Mott–Schottky equation, and this is consistent with I – V data analysis. At higher frequency, the carriers do not follow the ac signal and their density drops; and the flatband potential increases mainly due to the build-in potentials within ordered and amorphous regions in the sample. [ABSTRACT FROM AUTHOR]

Sub-micrometer-sized (0.33 μm) polycrystalline powders of calcium copper titanate (CCTO) were synthesized via the solgel method. Compacted calcined powders were sintered at 900 °C/2h to obtain porous (<80% density) pellets. Subsequently, ZnO or SnO2 pastes (∼10 μm grain size) were smeared on either side of the pellets and sintered at 1100 °C/15 h, which yielded dense (>95% density) ceramics. X-ray structural investigations revealed the presence of ZnO or SnO2 traces in the bulk of the CCTO ceramics. Scanning electron microscopy and energy dispersive spectroscopic studies confirmed the diffusion and the segregation of these oxides at the grain boundaries. The dielectric and varistor properties of the ZnO or SnO2 diffused samples were found to be superior to that of pristine CCTO ceramics. For instance, the dielectric constant (ɛ′) of ZnO diffused ceramics exhibited a value as high as 2.4 × 104 (1 kHz, at room temperature) and a dielectric loss (D) of 0.059. Similarly, SnO2 diffused ceramics exhibited a dielectric constant of 2.7 × 104 (1 kHz, at room temperature) associated with a dielectric loss of 0.047. The figure of merit of varistor performance, i.e., nonlinear coefficient (α = 10.6), of the SnO2 diffused sample is significantly higher than that of ZnO diffused (α = 7.4) and pristine CCTO (α = 4.5) ceramics. The dielectric data obtained for both the pristine and ZnO or SnO2 diffused ceramics were rationalized by invoking Cole–Cole analysis. The thermal activation energy was estimated from the temperature-dependent dielectric data besides current (I)–voltage (V) characteristics. Equivalent circuit modeling of the Nyquist plots demonstrated that the inclusion of ZnO and SnO2 layers in CCTO ceramics remarkably improved the grain boundary resistance (Rgb) by 5-fold and 20-fold, respectively, which resulted in making CCTO a better dielectric. This methodology of fabricating ceramics via interfacial engineering could pave the way for obtaining superior CCTO ceramics associated with exotic functional properties. [ABSTRACT FROM AUTHOR]

High-efficient microwave absorbers (MAs) with excellent absorption performance and lightweight characteristics have important applications in the military and civil. Here, we propose a dielectric-magnetic hybrid microwave absorber composed of a lattice of dielectric cylinders combined with thin magnetic cylinders backed by a perfect electrical conductor ground plane. The dielectric material that is designed as the dielectric cylinder is based on multi-walled carbon nanotubes-epoxy (MWCNT-EP). The MWCNT-EP is prepared and the S-parameters are measured by the standard transmission/reflection (T/R) method. The thin magnetic cylinder is based on a commercial magnetic material with a height of only 1 mm. With the coaction of magnetic loss and dielectric loss, the proposed microwave absorber's reflection loss is less than −20 dB under normal incident with a total height of 5 mm in the X-band. Besides, the dielectric-magnetic microwave absorber can maintain good absorption performance with different incident angles and polarizations. In this work, we provide a method to combine the properties of magnetic and dielectric material to construct the MA with high-efficient absorption performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The nonlinear dielectric properties of polyimide (PI) films, excited by high-intensity, AC electric fields, have been measured. This work highlights that nonlinear DC conduction is a component of the AC conductivity and dielectric loss response when surpassing a certain threshold field strength. An additional Poole–Frenkel polarization, induced by high-intensity, high-frequency fields, also contributes to the nonlinearity. This increases the dielectric losses through a charge de-trapping process, the so-called "jacking-up" effect. A novel expression that captures the large signal behavior of the complex permittivity is introduced using the Cole–Cole format. Finally, it is shown that the dielectric properties and power dissipation density in PI films remain fully linear and frequency-independent up to an AC electric field of EPF ∼100 Vrms/μm and more conservatively below a threshold field of EX ∼ 45 V/μm (i.e., end of the ohmic region). Consequently, polyimide-based insulated electronic devices that are designed to continuously operate below this threshold field (including both uniform and fringe fields) will remain immune to a frequency-dependent electrical aging. Their lifetime should not be affected in any way. [ABSTRACT FROM AUTHOR]

With the rapid development of electrical equipment and electronic devices, polymer-based dielectric nanocomposites with high-energy density and low dielectric loss for capacitive energy storage are in great demands. However, the traditional approaches to improve the dielectric constant of polymer by incorporating high loading of inorganic nanofillers with high dielectric constant are always at the expense of breakdown strength (Eb), resulting in limited improvement in energy density of polymer dielectrics. Here, ultralow loadings (≤1 vol. %) of barium titanate (BaTiO3, BT) nanoparticles were incorporated into polyetherimide (PEI) matrix for capacitive energy storage applications. The results show that the simultaneous enhancement of dielectric constant and breakdown strength is achieved in PEI-based nanocomposite with ultralow loading of BT nanoparticles. The nanocomposite with an ultralow loading of 0.4 vol. % BT nanoparticle exhibits a highest discharge energy density of 6.46 J/cm3 (4.8 times that of pure PEI film) and an acceptable charge–discharge efficiency of 77.6% at 500 MV/m. Furthermore, the nanocomposite exhibits improved high-temperature energy storage performance, good long-term reliability, and enhanced discharge capability. Therefore, nanocomposites based on ultralow loading of BT nanoparticles provide a promising approach for the development and application of high-energy-density polymer-based dielectrics. [ABSTRACT FROM AUTHOR]

In this paper, based on the airflow improvement mechanism of dragonfly wing veins, a vortex generator is designed at the leading edge of the suction surface to improve the flow condition of compressor cascades. The influence of the placement positions and geometric dimensions of the vortex generators on the flow field structure and aerodynamic performance is investigated by numerical simulation. The research reveals that vortex generators at the leading edge of the suction surface can generate induced vortices near the end wall, suppressing the accumulation of low-energy fluid in the corner region. This results in a backward shift of the separation initiation point, a reduction in the corner separation region along the pitch direction, and a reduction in flow loss. The vortex generators exhibit favorable characteristics with positive incidence angles. However, when the incidence angle is below the minimum loss incidence angle, the vortex generators increase the flow losses of the cascade. Optimum performance is achieved when the vortex generators are positioned at the start of the corner separation. The flow control influence initially increases and then decreases as the height of the vortex generators increases. Similarly, the control impact is enhanced and then weakened as the placement position moves away from the suction surface. The flow losses decrease by 10.3% when the vortex generators are placed at the junction between the end wall recirculation and the mainstream region at a height equal to 2% of the blade height. [ABSTRACT FROM AUTHOR]

A theory for presheath-like structures near probes biased at and above the plasma potential is developed for collisionless plasmas with an electron-neutral mean free path on the order of the chamber scale. The theory predicts presheath-like perturbations to the plasma that result from the free streaming of electrons and an effusion loss process from the chamber at the electrode. For these situations, a loss-cone-like velocity distribution function for electrons is predicted where the loss angle of the depletion region corresponds to the angular size of the electrode at a specified distance. The angle of the loss cone becomes 180° at the sheath edge. In comparison with a previous collisional electron presheath model that required electrons satisfy a Bohm criterion at the sheath edge [Scheiner et al., Phys. Plasmas 22, 123520 (2015)], the present work suggests that no such condition is needed for collisionless low pressure plasmas in the ≲ 10 mTorr range. The theory predicts the generation of a density depletion of roughly 0.5ne and an electron velocity moment of tens of percent of the electron thermal speed by the sheath edge in a presheath with a potential drop of less than T i / e. The range of this presheath perturbation is determined by the electrode geometry instead of the collisional mean free path. These predictions are tested against previously published particle in cell simulations and are found to be in good agreement. [ABSTRACT FROM AUTHOR]

Silicone rubber based lightweight composites have been prepared using nano carbon black (CB) as fillers to achieve broadband microwave absorption properties and electromagnetic interference (EMI) shielding over the 8–18 GHz frequency range. The effect of the filler material characteristics on percolation threshold and resultant electromagnetic (EM) properties of composites has been investigated. The composites are prepared by loading different filler fractions (wt. %) of three nano size CB having different characteristics, viz., CB1 (∼5–10 nm), CB2 (∼15–20 nm), and CB3 (∼30–40 nm) in a silicone rubber matrix. The volume resistivity measurements suggest low value of percolation threshold, i.e., 2 wt. % for CB1-rubber composite, 3 wt. % for CB2-rubber composites, as compared to 15 wt. % for CB3-rubber composite. Filler concentration dependent EM properties, i.e., dielectric constant and dielectric loss tangent (tan δe), are evaluated for all the CB-rubber composites. Furthermore, calculated reflection loss (RL) values for these composites indicate that 3 wt. % CB1-rubber, 5 wt. % CB2-rubber, and 18 wt. % CB3-rubber composites can provide more than 90% microwave absorption (RL > −10 dB) in X (8–12 GHz) and Ku (12–18 GHz) bands with thickness ∼2.7 and ∼1.9 mm, respectively. Interestingly, the composites with higher loading (15 wt. %) of CB1 in the rubber matrix are found to give EMI shielding effectiveness values of ∼ 42 dB over the 8–18 GHz frequency range. In conclusion, CB1-silicone rubber composites have been found to give the best performance among the three studied composites. This composite provides >90% microwave absorption over the X band with 2.7 mm thickness and over the Ku band with thickness 1.9 mm with lowest concentration of fillers, i.e., 3 wt. % CB1 in the rubber matrix, and hence found potential for development of lightweight microwave absorbers for stealth applications. [ABSTRACT FROM AUTHOR]

In this study, the microwave absorbing properties of epoxy composites filled with micro-sized MoS2 and carbon nanotubes (CNT)/MoS2 were investigated in the frequency range of 1–67 GHz. Sample characterization was performed using electron microscopy and Raman spectroscopy methods. Direct current (DC) conductivity, complex permittivity, and shielding properties of composite materials with 50 wt. % of MoS2 and 1.5–2 wt. %CNT/50 wt.%MoS2 were measured. The permittivity of 50 wt. % MoS2/epoxy composite was found to be equal to 7.3, decreasing monotonically down to 4.5 at 67 GHz, while the imaginary part is equal to 1 and does not change. The addition of 2 wt. % of CNTs increases the real part of permittivity ε r ′ up to 30 at 1 GHz (13 at 67 GHz) and also leads to a large increase of the imaginary part of permittivity, with the most pronounced relaxation peak ε r ′ ′ = 10 at 10 GHz. Such an increase of dielectric loss correlates with the increase of DC conductivity up to 3.2 × 10−5 S/m as compared to the two-phase composite 50 wt. %MoS2/epoxy (σdc = 1.7 × 10−9 S/m). It was shown that 50 wt. %MoS2/epoxy composite exhibited an effective microwave absorption bandwidth of 9.9 GHz at the sample thickness of 2.0 mm with reflection loss minimum of -20.0 dB at 51.5 GHz. 2 wt. %CNT/50 wt. %MoS2/epoxy composite with a thickness of 0.9 mm showed a reflection loss minimum of −38 dB at 20.2 GHz with the absorption bandwidth of 3.68 GHz. The influence of sample thickness on position, width, and depth of EMR absorption maximums for the composites filled with MoS2 and mixed filler CNT/MoS2 was also determined. [ABSTRACT FROM AUTHOR]

In this manuscript, we examine the electrical behavior of pulse laser deposition grown epitaxial (111) oriented CuO thin films using impedance spectroscopy to understand the microscopic origin of their relaxor-like characteristics. Temperature (T) dependent variation of the real part of dielectric permittivity (ε ′) shows a relaxor ferroelectric-like anomaly with Vogel–Fulcher relation fitting well with the observed dielectric behavior, and thus, pointing toward a relaxor ferroelectric nature of the CuO thin film. However, the loss tangent and frequency-dependent dielectric spectroscopy measurements suggest the need to further explore the different mechanisms to understand the origin of observed relaxor behavior. Deconvolution of the impedance spectra reveals that interfacial contributions dominate in the dielectric response. Moreover, deconvoluted capacitances are temperature-independent within the specified temperature range, thereby excluding the possibility of a ferroelectric transition suggested by ε ′ v s T data. The DC bias measurement of dielectric permittivity and I–V measurements reveal the MW (Maxwell–Wagner) nature of the observed dielectric anomaly. The measurements also suggest interface-limited Schottky conduction as the predominant conduction mechanism in the CuO thin films. This work demonstrates that the apparent relaxor behavior observed in the CuO thin film is related to extrinsic, i.e., interfacial polarization effect, instead of the intrinsic ferroelectric nature of the material. [ABSTRACT FROM AUTHOR]

The presence of amorphous oxide layers can significantly affect the coherent time of superconducting qubits due to their high dielectric loss. Typically, the surface oxides of superconductor films exhibit lossy and unstable behavior when exposed to air. To increase the coherence time, it is essential for qubits to have stable and low dielectric loss oxides, either as barrier or passivation layers. In this study, we highlight the robust and stable nature of an amorphous tantalum oxide layer formed on α-Ta (110) film by employing chemical and structural analyses. Such kind of oxide layer forms in a self-limiting process on the surface of α-Ta (110) film in piranha solution, yielding stable thickness and steady chemical composition. Quarter-wavelength coplanar waveguide resonators are made to study the loss of this oxide. One resonator has a Qi of 3.0 × 106 in the single photon region. The Qi of most devices are higher than 2.0 × 106. Moreover, most of them are still over 1 × 106 even after exposed to air for months. Based on these findings, we propose an all-tantalum superconducting qubit utilizing such oxide as passivation layers, which possess low dielectric loss and improved stability. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs), especially the FeCoNi-based HEAs with magnetic loss and dielectric loss, have attracted considerable attention in the field of electromagnetic-wave absorption (EMA). However, improper electromagnetic parameters of HEAs led to impedance mismatching, which considerably reduced its electromagnetic-wave absorbing efficiency. Dealloying in HEAs is an available approach to optimizing electromagnetic properties owing to its function of component tailoring and surface modification. Herein, FeCoNiCuAl HEAs were prepared by the high-energy balling method, and then, the as-milled powders were dealloyed in KOH solution with different concentrations. Undergoing the dealloying process, Al contents in FeCoNiCuAl HEAs decreased, while the surface area increased, which efficiently optimized impedance matching and promoted surface polarization loss. Profiting from these merits, samples A02 and A06 exhibit excellent EMA performance, with strong absorptions of −56.04 dB at 13.01 GHz and −56.12 dB at 6.88 GHz, corresponding to bandwidths of 3.29 GHz (1.69 mm) and 2.88 GHz (1.69 mm), respectively. [ABSTRACT FROM AUTHOR]

Low-temperature anomalies of dielectric permittivity of S n 2 P 2 S 6 crystals were investigated. It is shown that these phenomena have a relaxation character and the observed anomalies could be related to the small hole polarons dynamics with donor-acceptor compensation processes in lattice with tin and sulfur vacancies. To confirm it, we measured the dielectric properties of tin-enriched and sulfur-enriched crystals. It is shown that deviation from stoichiometry leads to a significant change in the low-temperature anomalies of dielectric losses. [ABSTRACT FROM AUTHOR]