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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]

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]

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]

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]

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]

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]

The ternary RGO/Fe3O4/SiO2 composites were prepared through a hydrothermal method and an annealing process. The Fe3O4 and SiO2 particles were in situ grown on the surface of reduced graphene oxide (RGO). The RGO, Fe3O4, and SiO2 were properly assembled to realize comprehensive electromagnetic wave-absorbing performance, which not only achieve synergy between the dielectric loss and the magnetic loss, but also possess satisfactory impedance matching. Based on the analysis of absorbing properties, the RGO/Fe3O4/SiO2-0.5 composite exhibits the optimal wave absorbing performance with the maximum reflection loss of −34.36 dB and an effective absorption bandwidth of 7.76 GHz at a matching thickness of 2.9 mm. The introduction of wave transparent and insulated SiO2 increases the propagation paths and optimizes the conductivity. Meanwhile, the construction of a heterogeneous interface promotes the interfacial polarization. The appropriate conductive network and the defect sites of RGO guarantee the conduction loss and dipole polarization. The natural resonance and exchange resonance from Fe3O4 jointly contribute to the magnetic loss. Therefore, this work provides a simple and flexible method for the synthesis and design of the heterostructure with multiple dissipation mechanism as a high-efficiency absorbent. [ABSTRACT FROM AUTHOR]

Carbon fibrous (CF) membranes were fabricated by electrospinning, thermal stabilization, and the carbonization process. The in-depth analyses of the CF membranes' composition, structure, and microwave absorption (MA) property demonstrate that the MA performance of the membranes is strongly correlated with the C/O ratio and CF framework's microstructure. A maximum absorption value of −23.4 dB is achieved at 800 °C, and this was synergistically enhanced to −42.5 dB with the addition of graphene nanosheets (GNSs). The special multilayered membranes containing dielectric loss CNSs and CFs making the balance between excellent impedance matching and the high loss characteristic could deliver an excellent MA property. With the facile and controllable synthesis of the GNS/CF membranes, a new approach to efficiently optimize and regulate its MA behavior is now possible. [ABSTRACT FROM AUTHOR]

A chaos patterned metasurface absorber (CPMA) with three strong absorption peaks and a wide bandwidth has been designed. This CPMA presents a single-layer sandwich structure, which not only enables easy optimization by adjusting the surface pattern and model size but also contributes to the continuous effective bandwidth (EBW, with an absorptivity larger than 90%) from the multiple adjacent absorption peaks. The continuous EBW is from 4.28 to 9.56 GHz with a bandwidth of 76.3%. Meanwhile, analyses on the distributions of the surface current, electric field, and power loss density illustrate that the absorption mechanisms are mainly magnetic coupling resonance and dielectric loss. The experimental results confirm the good absorption performance with multi-peak and wide bandwidth for the fabricated CPMA sample, which shows potential applications in the field of anti-electromagnetic interference. [ABSTRACT FROM AUTHOR]

Tunable materials have been extensively studied due to their potential applications in many electrical devices. High tunability has been practically achieved in a number of ferroelectric materials such as perovskite phases under usually high DC electric field of 10–100 kV/cm. In this work, single phased M-type barium ferrite ceramics with colossal permittivity accompanied by defect pair dipoles and giant tunability under super low DC bias were successfully prepared by the sol-gel method. Results show that Zr4+ ions substituted for Fe3+ in the spinel phase of ferrites. The concentration of Fe2+ increased from 37.23% to 43.22% and subsequently decreased to 36.72% with increasing Zr4+ ions from 0 to 0.1 and then continuously to 0.3, respectively. The highest content of Fe2+ was ∼43.22% and thus the maximum concentration of Fe2+/Fe3+ pair dipoles formed between Fe2+ generated and Fe3+ nearby appeared in the ferrites with Zr4+ doping of 0.1. Not only in Zr4+ doped ferrites but also in the ferrites with doping other high valent ions, Fe2+/Fe3+ pair dipoles formed and controlled permittivity. Giant permittivity of above 30 k appeared in the ferrites with Zr4+ content of 0.1–0.3 and was controlled by external bias to form tunability. The activation energy of modulation of defect pair dipoles was only ∼0.182 eV, which is 85% lower than 1.2 eV of traditional perovskite BaTiO3. High dielectric tunability of more than 65% with only a low DC electric field of <25 V/cm was obtained in BaFe11.9Zr0.1O19 ferrites, which was in high contrast to conventional ferroelectrics where a high DC bias of dozens of kV/cm was required. Similarly, dielectric tunability of ∼40% with a low electric field of <40 V/cm was exhibited in Nb5+ or Ti4+ doped barium ferrites. Such a high tunability controlled by an extremely low bias field in barium ferrite ceramics doped by the target ions might be promised for novel applications in tunable devices. [ABSTRACT FROM AUTHOR]

A simple physical model for evaluating propagation loss of a metal-coated dielectric terahertz (THz) waveguide with different metal film thicknesses was developed for those fabricated by three-dimensional printing and film coating techniques. Our model enables a comprehensive understanding of the propagation loss mechanism and two key values: the critical film thickness to behave like the bulk material and loss in a sufficiently thick film. To develop the model, in addition to reflection at the metal–dielectric interface, the thickness-dependent electrical conductivity of the metal film was considered. The model was validated by an in-house multi-channel Au-coated THz parallel-plate waveguide in the lowest transverse-electric mode. The estimated critical thickness of our Au film was 171–207 nm at 0.72–1.4 THz. Our model clarified the contribution of three loss components to the overall loss: penetration loss, ohmic loss by bulk conductivity, and ohmic loss by a decrease in conductivity due to thin-film effects. Evaluation of loss over a broader frequency range (0.03–3.0 THz), which corresponds to fifth- to sixth-generation mobile network, revealed that the critical thickness decreased by up to 1.0 THz but increased above this range due to the transition of the dominant loss component from penetration loss to ohmic loss by a decrease in conductivity. As all three loss components and the critical thickness depend on film quality, a deposition process to yield high-quality films is necessary for high-performance waveguides. Our model is applicable to various waveguides, including rectangular waveguides, at any frequency and with any metal film. [ABSTRACT FROM AUTHOR]

Adding functionalities to existing ferroelectric/ferromagnetic materials showed promising results with exciting physical mechanisms. Pure and bilayer films of strong ferromagnetic oxides, viz, BaFe12O19 (BaM) and La0.67Sr0.33MnO3 (LSMO), were fabricated by pulsed laser deposition. Polycrystalline samples of dense structure, uniform thickness, and monodispersed grain distributions were used to form capacitor-like stack geometry for dielectric and magneto-dielectric (MD) measurements. High dielectric constants at moderately high frequencies with increased relaxation times were observed for the bilayer film and are attributed to the BaM/LSMO strained interface, while Maxwell–Wagner polarization plays an insignificant role. Modeling of dielectric loss tangents and AC conductivity revealed localized carrier hopping between Fe ions in the bilayer film. Pronounced hysteresis loops with a small coercive field and increased saturation magnetization values of BaM/LSMO bilayers, as compared with BaM/Pt, are demonstrated at 300 K; where the role of mixed valence Mn ions in +3 and +4 states at the bottom LSMO electrode is highlighted. MD measurements with varying magnetic fields showed magnetically tunable, large MD coupling values (∼287%) for BaM/LSMO/Pt. The phenomenally high MD values are discussed based on ionic polarization, colossal magnetoresistance of LSMO, and magnetostriction at the BaM/LSMO interface. Our findings propose significant applications of ferromagnetic oxide bilayers in the emerging field of magneto-dielectric coupling devices. [ABSTRACT FROM AUTHOR]

Metamaterial absorbers are usually made of resonant structures backed by a metallic reflector, relying solely on the ohmic and dielectric losses generated by magnetic resonance. In this work, we apply an alternate approach to obtain absorption by overlapping magnetic and electric resonances in a conventional cut-wire-pair metamaterial. A terahertz absorber is designed following that approach achieving up to 99% absorption in simulations without employing a reflector, while the fabricated prototype absorbs up to 82% (excluding the loss of the silicon wafer) of the incident waves at 56 THz. The results empirically confirm that perfect absorption can be obtained using resonance superposition. In addition, the high absorption strength and the possibility to permit the transmission of the proposed metamaterial absorber make it different from other conventional ones. [ABSTRACT FROM AUTHOR]

The chemical reduction has often been exploited to improve the dielectric, piezoelectric, and flexoelectric response of the perovskite oxides. In this work, the effect of reduction on the dielectric properties of Na0.5Bi0.5TiO3-based ceramics was investigated in a broad temperature range from −130 to 175 °C. After the reduction of the ceramics, three dielectric anomalies were observed. The two dielectric anomalies at a low temperature exhibit a thermally activated dielectric relaxation characteristic with an activation energy of ∼0.3 eV. Evidence indicates that the two dielectric anomalies are related to the hopping of electrons between the defective lattice sites which has an interaction with the dipoles existing in the bulk and the region close to the ceramic surface, respectively. The third dielectric anomaly is observed around room temperature, and the frequency-independent dielectric constant and loss are greatly increased in the reduced ceramics. The origin of the dielectric anomaly is argued to be related to the interaction of water with the ceramic surface region. The reduction produces a large number of oxygen vacancies, facilitating the water adsorption on the surface of the reduced ceramics. The interaction greatly increases the migration and conduction of protons, generating a pronounced dielectric anomaly. We also show that the similar dielectric anomaly, though very weak, also appears in other unreduced perovskite-type oxides, indicating that the interaction of water with the surface is a common phenomenon in perovskite-type oxides. [ABSTRACT FROM AUTHOR]

Epitaxially grown superconductor/dielectric/superconductor trilayers have the potential to form high-performance superconducting quantum devices and may even allow scalable superconducting quantum computing with low-surface-area qubits such as the merged-element transmon. In this work, we measure the power-independent loss and two-level-state (TLS) loss of epitaxial, wafer-bonded, and substrate-removed Al/GaAs/Al trilayers by measuring lumped element superconducting microwave resonators at millikelvin temperatures and down to single-photon powers. The power-independent loss of the device is (4.8 ± 0.1) × 10 − 5 , and the resonator-induced intrinsic TLS loss is (6.4 ± 0.2) × 10 − 5 . Dielectric loss extraction is used to determine a lower bound of the intrinsic TLS loss of the trilayer of 7.2 × 10 − 5 . The unusually high power-independent loss is attributed to GaAs's intrinsic piezoelectricity. [ABSTRACT FROM AUTHOR]

In this work, we report nearly single oriented {001}-textured ferroelectric PbZr 0.52 Ti 0.48 O 3 thin films grown by pulsed laser deposition onto AISI 304 stainless steel substrates. Pt, Al 2 O 3 , and LaNiO 3 buffer layers promote the PbZr 0.52 Ti 0.48 O 3 {001} texture and protect the substrate against oxidation during deposition. The dominant {001} texture of the PbZr 0.52 Ti 0.48 O 3 layer was confirmed using x-ray and electron backscatter diffraction. Before poling, the films exhibit a permittivity of about 350 at 1 kHz and a dielectric loss below 5%. The films display a remanent polarization of about 16.5 μ C cm − 2 and a high coercive field of up to E c = 135.9 kV cm − 1 . The properties of these PbZr 0.52 Ti 0.48 O 3 thin films on stainless steel are promising for various MEMS applications such as transducers or energy harvesters. [ABSTRACT FROM AUTHOR]

The effect of Mn and Fe dopants on the electromechanical and electrochemical properties of 0.88[Bi0.5Na0.5]TiO3–0.08[Bi0.5K0.5]TiO3–0.04[Bi0.5Li0.5]TiO3 piezoceramic is investigated with particular emphasis on complex impedance in the temperature range from 450 to 600 °C. The impedance spectra have been simulated with equivalent circuits in order to extract bulk and grain boundary characteristics and to determine activation energies of conduction. Mn and Fe dopants considerably enhance the mechanical quality factor and decrease the dielectric loss compared to the undoped composition. Mn doping leads to dramatically higher resistivity in the bulk and a modest increase in the bulk activation energy. On the other hand, conductivity increases dramatically via Fe doping with a significant lowering of activation energy in the bulk and corresponding raising of the activation energy at grain boundaries in comparison to Mn-doped and undoped ceramic. The bulk conductivity of Fe-doped piezoceramic reaches as high as 0.01 S cm−1 at 600 °C. [ABSTRACT FROM AUTHOR]

Morphotropic phase boundary (MPB) composition 0.94Na0.5Bi0.5TiO3–0.06BaTiO3 (NBT–6BT) has received industrial acceptance in certain aspects such as ultrasonic cleaners to replace those of lead-based systems. While detailed structure–property analysis on NBT–6BT is mostly confined to room temperature and above, less attention is paid with regard to their structure and property understanding below room temperature. In this work, utilizing the complementarity of Raman spectroscopy, x-ray diffraction, and neutron powder diffraction, we unravel low temperature polar-structural behavior of the MPB composition. While x-ray diffraction shows the persistence of a cubic like global structure in the temperature interval from 300 to 100 K, neutron diffraction reveals a structural crossover from long period modulated to non-modulated P4bm + R3c phase coexistence at ∼150 K. We show that the tendency of growing ferroelectric ordering with reducing temperature is responsible for the structural crossover. Concurrence of weak anomaly in dielectric loss (tan δ) at the same temperature seems to be correlated to the structural crossover. [ABSTRACT FROM AUTHOR]

High-performance electromagnetic wave absorption materials constitute key components of microelectronic devices. Traditional absorbents possess magnetic losses and/or dielectric losses, while the experimental approach for their simultaneous enhancement is still lacking. Here, we demonstrate that the core/shell structural Ni@C nanocapsules, functionalized by atomic-scale oxygen substitutions that can be formed catalytically by highly defective graphitic structure, present enhanced dielectric loss capacities at gigahertz. In particular, >90% of the microwave energy could be attenuated for a planar absorber with a thickness down to 1–1.5 mm at 7.6–13.8 GHz. Experimental characterizations coupled with density functional theory calculations further evidence that the capacity enhancement is ascribed to the structure breaking at the heterogeneous substitutional zones, resulting in the intrinsic polarization of carbon–oxygen heterostructures. The present study shows a new mentality of designing for optimizing electromagnetic wave absorption materials and also has pointed out the atomic-scale structural origin of the electromagnetic response performance. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) composite thin films are promising candidates for novel applications in future nanoelectronics, spintronics, memory, and other multifunctional devices as they exhibit much higher ME coupling and transition temperatures (Tc) than well-known single phase multiferroics discovered to date. Among the three types of multiferroic composite nanostructures, (2–2) layered and (1–3) vertically aligned composite nanostructures exhibit comparatively smaller ME coupling due to different shortcomings that restrict their use in many applications. Here, we study the morphological, piezoresponse force microscopic (PFM), ferroelectric, magnetic, and magnetodielectric properties of 0–3 [magnetic nanoparticles (0) homogeneously distributed in ferroelectric matrices (3)] multiferroic composite thin films. The Pb(Fe0.5Nb0.5)O3 (PFN)–Ni0.65Zn0.35Fe2O4 (NZFO) particulate composite films were synthesized by pulsed laser deposition. These particulate composite thin films are completely c-axis oriented with very low surface roughness. We observed magnetic and ferroelectric Tc above room temperature (RT) for all composite thin films. The PFN–NZFO 0–3 composites exhibit large polarization, high saturated magnetization with low coercive field, and low dielectric loss along with magnetodielectric coupling at RT. These nanocomposites might be utilized in next generation nano/microelectronics and spintronic devices. [ABSTRACT FROM AUTHOR]

In this paper, temperature dependance of induced dielectric and piezoelectric properties in the [001]-oriented predirect current poling (DCP) of the 0.25Pb(In1/2Nb1/2)O3-0.43Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (0.25PIN-0.43PMN-0.32PT) single crystals near morphotropic phase boundary was investigated using the alternating current treatment (ACT). By the optimized ACT conditions of 1 kV/mm at 50 Hz over 20 cycles, the dielectric permittivity (ɛ33T/ɛ0) and piezoelectric coefficient (d33) at room temperature of the DCP-ACT crystal were improved to be 7120 and 2610 pC/N, which were 48% and 54% higher than that of the DCP crystal (ɛ33T/ɛ0 = 4800, d33 = 1700 pC/N). Based on the temperature dependence of dielectric permittivity and dielectric loss of the DCP-ACT crystal, the induced monoclinic phases (MA and MC) were involved in the phase transition process from a rhombohedral phase to a tetragonal phase. The phase transition temperatures TR-MA of 116 °C of the DCP-ACT crystal showed about 10 °C higher than that of DCP. Meanwhile, ɛ33T/ɛ0 of the DCP-ACT crystal at TR-MA and in the tetragonal phase region, at around 110 °C and 130 °C, were 160% and 390% higher than those of the DCP crystal, respectively. The ultrahigh ɛ33T/ɛ0 = 17 000 of the DCP-ACT crystal at 130 °C may relate to the nanoscale heterogeneous polar-regions induced by ACT. The ACT is a promising way to enhance the dielectric and piezoelectric performance of the pre-DCP 0.25PIN-0.43PMN-0.32PT single crystals with broadened temperature range for device applications. [ABSTRACT FROM AUTHOR]

Sodium niobate (NaNbO3, NNO) has attracted considerable attention as a potential lead-free candidate for high-density energy-storage capacitors. An economical, environment-friendly, and low-temperature-synthesized route of NNO films is highly desirable for practical applications. In this study, a novel water-based solgel route was designed for the growth of NNO films, and the effects of annealing temperatures (400–600 °C) on microstructure and physical properties were investigated. By increasing the annealing temperature, the quality of (001)-preferred NNO films was improved, but a higher annealing temperature (e.g., 600 °C) induced the secondary phase, resulting in the degradation of electrical properties. As annealed at the optimum temperature of 500 °C, the highly (001)-preferred NNO film possessed advantageous characteristics including the largest difference between maximum polarization and remanent polarization (e.g., 26 μC/cm2 at 300 kV/cm), the maximum dielectric constant, and the minimum dielectric loss (e.g., 241.68 and 0.06 at 10 kHz). These results demonstrate a promising option toward solution-processed Nb-containing perovskite oxides through water-based sol-gel routes for energy-relevant applications. [ABSTRACT FROM AUTHOR]

Atmospheric water adsorbed by porous materials may significantly change its electrodynamic response in a wide frequency range. Mechanical and chemical stabilities of silicon dioxide along with a proven manufacturing method of porous SiO2 samples made it convenient for studying the effects of moisture adsorption on various parameters of the porous media. We report the dielectric properties of SiO2-based nanoporous glass in the frequency range of 20 Hz–400 THz at ambient atmospheric conditions and at a low residual pressure of ≤1 mbar. We observed a significant low-frequency dispersion of the complex dielectric permittivity and enhancement of dielectric loss for the porous sample exposed to the ambient moisture. In the terahertz range, the change in dielectric response is smaller and correlates with the moisture saturation of the sample. [ABSTRACT FROM AUTHOR]

The glass of 30SiO2–35Li2O–35Nb2O5 (mol. %) composition was fabricated by using the melt-quenching technique. Three different heat-treatments were provided at 650 °C for 3, 4, and 6 h soaking time in order to control LiNbO3 crystallization. The presence of LiNbO3 crystals was confirmed using X-ray diffraction and Raman spectroscopy techniques. The optical study showed a decrease in transparency from 80% to 40% at 600 nm wavelength with an increase in LiNbO3 crystallization. Moreover, the blue shift was observed in the absorbance edge position and the bandgap was increased from 2.73 to 3.06 eV with an increase in LiNbO3 crystallization. The moderate dielectric constant (∼27–31) along with very low dielectric loss (∼0.008–0.06) was achieved at 1000 kHz and 30 °C in the case of LiNbO3 crystallized glass ceramics during the dielectric study. Moreover, the dc conductivity was found to decrease with the increase in LiNbO3 crystallization. During the nanoindentation study, the increasing trend was observed in hardness (∼7–11 GPa) and reduced modulus of elasticity (∼125–160 GPa) values with the increase in LiNbO3 crystallization. The glass ceramic heat-treated for 3 h could be used for nonlinear optical and other optical applications due to its adequate transparency and promising dielectric and mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, the significant electromechanical properties of the novel high-temperature piezoelectric single crystals YCa4O(BO3)3 (YCOB) were fully characterized over the temperature range from room temperature to 800 °C, including the dielectric, elastic, and piezoelectric properties, and electromechanical coupling coefficients and mechanical quality factor. More importantly, the complex coefficients were completely determined which take into account the mechanical and electrical losses of the material and, therefore, can describe the crystal behavior more accurately. The complete measurement procedures and calculation methods required to obtain all of these parameters were proposed. YCOB resonators with 23 different types of orientations were designed and measured, and all of the independent dielectric, piezoelectric, and elastic coefficients (4, 10, and 13, respectively), 6 important coupling factors, and the mechanical quality factor were determined. It was found that (1) the dielectric permittivity and loss increase dramatically and nonlinearly with the rise of temperature; (2) the elastic compliance constants basically increase linearly as the temperature rises, while the stiffness constants decrease linearly; (3) the piezoelectric charge constants d i j increase slightly with the elevated temperatures; (4) the coupling factors and mechanical quality factor decrease linearly with an increase of the temperature, and the coupling factors are in the range of 0.005–0.052, and the quality factor drops from 10 300 to 1300 with the temperature increasing from room temperature to 800 °C. [ABSTRACT FROM AUTHOR]

Pure hydroxyapatite (HAp) semiconducting microrods with very low dielectric loss have been synthesized in aqueous media of pH values 6, 8, and 10 by the hydrothermal method. Samples are characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectra analyses. The optical bandgap energies of these samples are found to be within the semiconducting range (∼3–4 eV). FESEM and TEM image analyses reveal the formation of microrods and reduction of the average length of the rods with increasing pH values. A core-shell-like microrod structure has been observed in the sample with pH value 6. The charge carrier follows an adiabatic small polaron hopping mechanism. The dielectric loss values are very small compared to that of other ceramic oxides which is very advantageous for electronic applications. Correlated barrier hopping model is the dominant charge transport mechanism within the samples with maximum barrier heights of 0.25 eV, 0.26 eV, and 0.27 eV for samples with pH values 6, 8, and 10, respectively. Nonideal Debye type relaxation appears within the material when the AC field is applied for temperatures above 100 °C. [ABSTRACT FROM AUTHOR]

Potassium-ion-doped MnO2 has been successfully synthesized using the hydrothermal method, and the influence of the doped potassium ions on the electrical conductivity and permittivity is studied. X-ray powder diffraction, scanning electron microscopy, electron-probe micro-analysis, and a vector network analyzer are used to perform characterization. The densities of states of doped and undoped MnO2 tunnel structures are also discussed based on first-principles calculations. Results show that the conductivity and dielectric resonance of MnO2 can be elevated by means of K+ doping. The conductivity of K+-doped MnO2 prepared at different reaction times shows a decreasing trend and is generally 1 order of magnitude higher than that of pure MnO2. The electrical conductivity of K+-doped MnO2 (R3) shows the highest value of 3.33 × 10−2 S/cm at the reaction time of 24 h, while that of pure MnO2 is 8.50 × 10−4 S/cm. When treated with acid, the conductivity of samples remains basically stable along with the increase of treatment time. In addition, acid treatment plays a very significant role in controlling the amount of K+ ions in crystals. The K+ contents of acid-treated samples are 5 times lower than that of the untreated R1. The dielectric losses of the samples with different reaction times are enhanced markedly with frequency increment. The complex permittivity of pure MnO2 only exhibits a resonance at ∼12 GHz, while K+-doped MnO2 exhibits another resonance behavior at ∼9 GHz. The capacity of the dielectric property in the net structure is enhanced by the interfacial polarization, dielectric relaxation, multiple internal reflections, and multiple scattering benefiting. [ABSTRACT FROM AUTHOR]

Broad-band dielectric and phonon response of Nb-doped (1-x)Pb(Zr1-yTiy)O3-xCoFe2O4 composites with x=10%–30% was investigated between 0.1 MHz and 100 THz. At room temperature, a broad distribution of relaxation times causes a constant dielectric loss below 1 GHz. Above room temperature, a strong Maxwell-Wagner relaxation process dominates below 1 GHz due to the conductivity of CoFe2O4 (CF). Two additional relaxation processes are seen between 1 GHz and 1 THz. The lower-frequency one, coming from domain wall motion, disappears above TC≈650 K. The higher-frequency component slows down on heating towards TC, because it is the central mode, which drives the ferroelectric phase transition. Time-domain THz transmission and infrared reflectivity spectra reveal a mixture of polar phonons from both ferroelectric Nb-doped Pb(Zr,Ti)O3 (PZTN) and magnetic CoFe2O4 (CF) components, while the micro-Raman scattering spectra allow to study phonons from both components separately. Similar temperature behavior of phonons as in the pure PZTN and CF was observed. While in CoFe2O4 the Raman-active phonons gradually reduce their intensities on heating due to increasing conductivity and related reduced Raman-scattering volume, some phonons in PZTN disappear above TC due to change of selection rules in the paraelectric phase. Like in the pure Pb(Zr,Ti)O3, the soft phonon and central modes were also observed. [ABSTRACT FROM AUTHOR]

In this paper, a metamaterial electromagnetic energy harvester constructed via the capacitive loading of metal circular split rings is presented. Each energy-harvesting cell is loaded with a resistance that imitates the input impedance of a rectifier circuit. Specifically, the metamaterial energy harvester has high selective harvesting for left- and right-handed circularly polarized waves. Here, the energy absorption is mostly induced by the resistive load; thus, effective energy harvesting can be achieved. Moreover, the proposed energy harvester exhibits a high-efficiency harvesting for right-handed circularly polarized waves over a wide range of incident angles. Further, a transmission line model is adopted to interpret the energy harvesting mechanism, which shows that a good impedance matching and low dielectric loss can further enhance the harvesting efficiency. To demonstrate the design, a 15 15 unit-cell prototype is fabricated and measured, and the measured results reasonably agree with the simulated ones. [ABSTRACT FROM AUTHOR]

The development of complex oxides that can be processed at temperatures at and below 350 °C is desirable for their integration onto polymeric substrates, enabling their use in flexible applications. Nanocomposite films consisting of a nanocrystalline fluorite related to delta-bismuth oxide in an amorphous matrix were prepared via chemical solution deposition. These solutions were batched with the composition Bi1.5Zn0.9Nb1.35Ta0.15O6.9. The nanocomposite had a relative permittivity of 50±2 and dielectric losses on the order of 0.03±0.01. For measurement frequencies of 1 kHz and 10 kHz, the nanocomposite demonstrated a breakdown strength of 3.8 MV/cm, and a roomtemperature energy storage density of approximately 40.2±1.7 J/cm3. To determine the suitability of the nanocomposite films for use in flexible applications, flexible nanocomposite films underwent repetitive compressive and tensile bending around a minimum bend diameter of 7mm, which corresponded to a strain of 0.10%. After bending the films 30 000 times, the energy storage density of the films was unchanged, demonstrating that nanocomposite bismuth zinc niobate tantalate films are suitable for flexible energy storage applications. [ABSTRACT FROM AUTHOR]

Nonmonotonic thermal dependence of dielectric relaxation of water has been observed in hydrated graphite oxide (GO). Graphite oxide prepared via Hummers method then imbued with specific water contents were characterized, with 13C and 1H nuclear magnetic resonance spectroscopies, X-ray photoelectron spectroscopy, ambient- and variable-temperature X-ray diffractometries, as well as thermogravimetric analysis. Pressed pellets provided with either conducting or blocking electrodes yielded dielectric loss, which was shown to originate from dielectric relaxation of the confined water. Three relaxation processes were observed in impedance spectroscopy. Our previous work has identified two different types of water in GO, namely, intercalated water and water in inter-grain voids. P1 expresses the reorientation of water confined inside inter-grain voids, and P2, the rotation of intercalated water molecules confined in interlayers. The present work reveals a new process P3, which also relates to intercalated water. It slows down with temperature, and this apparent anomaly is explained by the decrease in water content and consequent narrowing of interlayer spacing in graphite oxide, as confirmed by characterization techniques. The present study should contribute to our understanding of surface water dynamics. [ABSTRACT FROM AUTHOR]

High energy density polymer materials are desirable for a broad range of modern power electronic systems. Here, we report the development of a new class of polymer dielectrics based on polyurea and polythiourea, which possess high thermal stability. By increasing the dipole density, the dielectric constant of meta-phenylene polyurea and methylene polythiourea can be increased to 5.7, compared with aromatic polyurea and aromatic polythiourea, which have a dielectric constant in the range of 4.1-4.3. The random dipoles with high dipolar moment and amorphous structure of these polyurea and polythiourea based polymers provide strong scattering to the charge carriers, resulting in low losses even at high electric fields. Consequently, this new class of polymers exhibit a linear dielectric response to the highest field measured (>700 MV/m) with a high breakdown strength, achieving high energy density (>13 J/cm3) with high efficiency (>90%). [ABSTRACT FROM AUTHOR]

In this work, classical Bruggeman symmetric and Looyenga mixing rules were used together with a general mixing model to estimate the permittivities and loss tangents of polymer composites in order to make rational filler selections. Eight different fillers were used and compared with theoretical polymer composites. Permittivity levels of the composites were between 2.1 and 70 in the frequency range of 2.5-8 GHz. Results showed that rational selections of fillers also provided better properties of composites when using low permittivity instead of high permittivity filler. However, in certain permittivity targets, better properties were achieved with high permittivity filler. The selections were based on the required volume ratios of fillers and total loss tangents of the composites. Theoretical results correlated well with previously reported values. [ABSTRACT FROM AUTHOR]

Loss reduction is critical to develop Ba1-xSrxTiO3 thin film tunable microwave dielectric components and dielectric energy storage devices. The presence of ferroelectricity, and hence the domain wall contributions to dielectric loss, will degrade the tunable performance in the microwave region. In this work, residual ferroelectricity-a persistent ferroelectric response above the global phase transition temperature-was characterized in tunable dielectrics using Rayleigh analysis. Chemical solution deposited Ba0.7Sr0.3TiO3 films, with relative tunabilities of 86% over 250 kV/cm at 100 kHz, demonstrated residual ferroelectricity 65 °C above the ostensible paraelectric transition temperature. Frequency dispersion observed in the dielectric temperature response was consistent with the presence of nanopolar regions as one source of residual ferroelectricity. The application of AC electric field for the Rayleigh analysis of these samples led to a doubling of the dielectric loss for fields over 10 kV/cm at room temperature. [ABSTRACT FROM AUTHOR]

The Na-doped Y2/3Cu3Ti4O12 system has been prepared and investigated. Na doping facilitates the formation of oxygen vacancies, which is of great benefit to the growth of the grain size. Proper amount of Na substitution in NaxY(2-x)/3Cu3Ti4O12 ceramics makes the dielectric loss significantly decreased. As x=0.050, Na0.050Y0.650Cu3Ti4O12 ceramics exhibit the lowest dielectric loss (about 0.022 at 1 kHz) and a relatively high dielectric constant (about 7500 at 1 kHz). The lowered dielectric loss is closely associated with the enhanced resistance of grain boundary. The conduction and dielectric processes of grain boundary become much more difficult after Na doping. Impedance analysis suggests that the same charge defects are responsible for the conduction and dielectric relaxation behaviors of grain boundary. Scaling behaviors indicate that the physical nature of their dielectric relaxation and conduction behavior are independent of the measurement temperature and the Na concentration. [ABSTRACT FROM AUTHOR]

Temperature-dependent domains back-switching behavior and nonlinear dielectric response were studied in 200 nm fresh and aged PbZr0.4Ti0.6O3 thin films to compare domain walls motion under large and small signals. Expected thermally activation of domains back-switching and dielectric nonlinearity were observed at low temperature, however, abnormal thermally inhibited behavior occurred at higher temperatures. Such phenomenon was found in both fresh and aged films and the ageing process magnified such thermally inhibited effect. Analyzing nonlinear dielectric response with Rayleigh law suggested that the interaction between domain walls and pinning centers was strengthened at high temperature especially after ageing. Promoted pinning effect by rising temperature could reduce dielectric loss and this is practical for high temperature applications of ferroelectrics. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF) and (Ba0.5Sr0.4Ca0.1)TiO3 (BSCT) are used as matrix and fillers, respectively, to prepare polymer functional composites by solution casting with N,N-dimethyl formamide as a solvent. It is found that the addition of BSCT has significant influence on the crystallization, melting, and glass transition behaviors of the PVDF matrix. The dielectric properties of the BSCT/PVDF composites are studied over a wide frequency range from 100 Hz to 1 GHz and a wide temperature range from -50°C to 100°C to explore the dependences of frequency and temperature. High dielectric constant (E) up to 132 at 100 Hz and low dielectric loss (tan d) down to 0.0045 at 1 GHz are achieved for the BSCT/PVDF composites. The obtained data of e are also theoretically fit by different models, and the modified Lichtenecker equation and Jayasundere-Smith equation show the best match. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

In this paper, we present the analysis of the dielectric (dielectric constant, dielectric loss, a.c. conductivity) and electrical properties (I-V characteristics) of pristine and nitrogen ion implanted polycarbonate. The samples of polycarbonate were implanted with 100 keV N+ ions with fluence ranging from 1 x 1015 to 1 x 1017 ions cm-2. The dielectric measurements of these samples were performed in the frequency range of 100 kHz to 100 MHz. It has been observed that dielectric constant decreases whereas dielectric loss and a.c. conductivity increases with increasing ion fluence. An analysis of real and imaginary parts of dielectric permittivity has been elucidated using Cole-Cole plot of the complex permittivity. With the help of Cole-Cole plot, we determined the values of static dielectric constant (ϵs), optical dielectric constant (ϵ∞), spreading factor (α), average relaxation time (τ0), and molecular relaxation time (τ). The I-V characteristics were studied using Keithley (6517) electrometer. The electrical conduction behaviour of pristine and implanted polycarbonate specimens has been explained using various models of conduction. [ABSTRACT FROM AUTHOR]