Permittivity Peak Research Articles

Dynamic permittivity of confined water under a static background field.

Molecular and collective reorientations in interfacial water are by-and-large decelerated near surfaces subjected to outgoing electric fields (pointing from surface to liquid, i.e., when the surface carries positive charge). In incoming fields at negatively charged surfaces, these rates show a nonmonotonic dependence on field strength where fastest reorientations are observed when the field alignment barely offsets the polarizing effects due to interfacial hydrogen bonding. This extremum coincides with a peak of local static permittivity. We use molecular dynamics simulations to explore the impact of background static field on high frequency AC permittivity in hydration water under an electric field mimicking the conditions inside a capacitor where one of the confinement walls is subject to an outgoing field and the other one to an incoming field. At strong static fields, the absorption peak undergoes a monotonic blue shift upon increasing field strength in both hydration layers. At intermediate fields, however, the hydration region at the wall under an incoming field (the negative capacitor plate) features a red shift coinciding with maximal static-permittivity and reorientation-rate. The shift is mostly determined by the variation of the inverse static dielectric constant as proposed for mono-exponentially decaying polarization correlations. Conversely, hydration water at the opposite (positively charged) surface features a monotonic blue shift consistent with conventional saturation. The sensitivity of absorption peaks on the field suggests that surface charge densities could be deduced from sub-THz dielectric spectroscopy experiments in porous materials when interfaces accommodate a major fraction of water contained in the system.

Synthesis and Characterization of the Electrical and Energy Storage Properties of New Barium Titanate - Europium Titanate Solid Solution

In the present work, the investigation of the structural, dielectric, ferroelectric and energy storage properties of polycrystalline samples of (1-x)BaTiO3 – xEuTiO3 (BT-ET) solid solution materials prepared by conventional solid-state reaction method has been carried out. X-ray diffraction analyses have revealed the formation of a single-phase tetragonal structure with the P4mm space group. Furthermore, the temperature dependence of the dielectric constants marked the presence of the following sequence of structural phase transitions, namely from rhombohedral to orthorhombic, from orthorhombic to tetragonal and from tetragonal to cubic phase transitions with the increase of temperature. A diffuse phase transition has been observed from the dielectric permittivity peak and has been analyzed using the modified Curie-Weiss law and the degree of diffuseness is found to be in the range of 1.16 - 1.76 due to the existence of different states of polarization. A phase diagram has been established based on the temperature-dependent dielectric permittivity studies. The room temperature ferroelectric properties point to a coercive field larger than that of BaTiO3 ceramics. Broad dielectric peaks associated with diffuse phase transition appear in a wide temperature range (40 - 100 °C) with the highest dielectric permittivity ε’ = 6498 found in the x = 0.05 ceramics. Moreover, an improved energy storage performance is obtained in the 0.95BaTiO3-0.05EuTiO3 ceramic with a recoverable energy density of Wrec = 0.797 J/cm3, coupled with an efficiency η = 73% at 170 kV/cm and the highest storage energy density of Wst = 1.571 J/cm3 is obtained for 0.90BaTiO3-0.10EuTiO3, which is superior to other lead-free BT-based ceramics. All these features demonstrate that the BT-ET ceramics can be widely used in energy storage applications and also in high-temperature multilayer capacitors for automotive, aerospace and related industries.

Comprehensive study of the structural properties and dielectric responses of Ba(2-x)Sr(x)GdFeNb4O15 materials

A comprehensive investigation has been conducted on Ba(2-x)Sr(x)GdFeNb4O15 powders. These powders were synthesized through the conventional solid-state reaction. X-ray diffraction analysis at room temperature has demonstrated that the samples adopt the TTB-structure, exhibiting the space-group P4/mbm. The Raman spectra of the samples exhibit remarkable similarity, yet distinct bands at different wave numbers, indicative of the varying modes of the MO6 octahedra. The dielectric studies have uncovered intriguing findings, including a high dielectric constant and a broad permittivity peak. Remarkably, the Curie temperature varies with the substitution rate, yet remains frequency-independent, a clear indication of these materials’ classical ferroelectric behavior.

Voxelotor and Red Blood Cell Pyruvate Kinase Activator Affect Clot Strength in Sickle Cell Disease

Introduction: Sickle cell disease (SCD) is a common genetic red blood cell (RBC) disorder that results from a single substitution of valine for glutamic acid in the β-globin gene, resulting in sickle hemoglobin (HbSS). Under hypoxia, HbS polymerizes and forms fibers within the RBCs, thus making the cells rigid, deformed, and sickle-shaped [1]. Deformed RBCs influence the compactness and dynamics of blood clots [2]. In addition, people with SCD are susceptible to thrombophilia [2,3,4]. Recently, there has been a heightened interest in ameliorating SCD using RBCs pyruvate kinase (PKR) activators, which increase ATP and decrease 2,3 DPG, resulting in increased oxygen affinity and improved RBCs deformability [5]. Voxelotor is also an oxygen affinity-modifying drug, recently FDA-approved. Voxelotor delays deoxy-HbSS formation, preventing in vitro HbSS polymerization and RBC sickling, thus improving RBC deformability [6]. The in vitro impact of PKR activators and Voxelotor on blood clotting in clinical samples from people with SCD has not been examined. Here we use a microfluidic dielectric sensor, termed ClotChip ® [7,8], to investigate the effects of Voxelotor and a PKR activator on the clotting time and clot strength of samples from people with SCD. Methods: Venous blood samples were collected in sodium-citrate from subjects with homozygous HbSS and healthy volunteers (HbAA) under an IRB-approved protocol. ClotChip ® microsensors were fabricated as previously described [7]. Blood samples were centrifuged at 200 g for 10 min. Plasma and buffy coats were removed and stored at 4 °Cfor 6 hours. Isolated, washed RBCs were then re-suspended in PBS at 20% hematocrit and then mixed with 67 mg/mL of Voxelotor (GBT440; Selleckchem) to a final concentration of 600 µM (in DMSO) or a PKR activator (PKR activator 3; MedChem Express) at 10 mM (in DMSO) and incubated at 37 °Cfor 6 hours. For controls, HbSS- or HbAA-containing RBCs at 20% hematocrit were mixed with PBS containing 0.5% v/v DMSO and incubated at 37 °C for 6 hours. After incubation, HbSS+Vox, HbSS+PKR, and control samples were centrifuged at 500 g for 10 min to remove PBS. Each sample's plasma was used to reconstitute RBCs at 20% hematocrit. CaCl 2 was added to the samples to induce coagulation, and the samples were injected into the ClotChip ® microfluidic sensors. An Agilent 4294A impedance analyzer was used to obtain the ClotChip ® readout curve defined as the temporal variation of the normalized real part of blood dielectric permittivity at 1 MHz (see Figure 1A). Based on our previous studies [7,8], the time to reach a permittivity peak (T peak) parameter was taken to indicate the clotting time, whereas the maximum change in permittivity after the peak (ΔƐ r,max) parameter was taken to indicate the clot strength. Data are reported as mean ± standard deviation (SD). Results: We analyzed the ClotChip ® T peak and ΔƐ r,max readout parameters for HbSS (n=11), HbSS+Vox (n=11), HbSS+PKR (n=11), and HbAA control (n=8) samples ( Figure 1B). The clot strength was ~50% higher in HbAA than HbSS (HbAA vs. HbSS: p= 0.001, Mann-Whitney test). However, when the SCD samples were treated with Voxelotor, the clot strength was observed to increase by ~10% (HbSS vs. HbSS+Vox, p=0.01, Paired t-test). Treatment with a PKR activator increased the clot strength by ~30% (HbSS vs. HbSS+PKR, p=0.003, Figure 1B). A significant difference was observed in the clotting time between HbAA vs. HbSS (p=0.001) but treatment with Voxelotor or a PKR activator did not change the clotting time for HbSS (HbSS vs. HbSS+Vox, p=0.43; HbSS vs. HbSS+ PKR, p=0.29) ( Figure 1B). (p values were determined using a non-parametric Mann-Whitney test and paired t-test). Discussion : We found that treatment of HbS-containing RBCs with a PKR activator or voxelotor improves clot strength but not clotting time. PKR activators improved the strength of the clot significantly more than Voxelotor. Patients with SCD had a faster clotting time than healthy participants, which agrees with earlier researchers on hypercoagulability in SCD [4]. These data suggest that HbS polymerization and RBC health affect clot characteristics but not clot kinetics in SCD. Further investigations may be required to relate RBC deformability, which is well-known to impact SCD pathophysiology, to blood clotting and venous thromboembolism.

A Multichannel Portable Platform With Embedded Thermal Management for Miniaturized Dielectric Blood Coagulometry.

This article presents a standalone, multichannel, miniaturized impedance analyzer (MIA) system for dielectric blood coagulometry measurements with a microfluidic sensor termed ClotChip. The system incorporates a front-end interface board for 4-channel impedance measurements at an excitation frequency of 1 MHz, an integrated resistive heater formed by a pair of printed-circuit board (PCB) traces to keep the blood sample near a physiologic temperature of 37 °C, a software-defined instrument module for signal generation and data acquisition, and a Raspberry Pi-based embedded computer with 7-inch touchscreen display for signal processing and user interface. When measuring fixed test impedances across all four channels, the MIA system exhibits an excellent agreement with a benchtop impedance analyzer, with rms errors of ≤0.30% over a capacitance range of 47-330 pF and ≤0.35% over a conductance range of 2.13-10 mS. Using in vitro-modified human whole blood samples, the two ClotChip output parameters, namely, the time to reach a permittivity peak (Tpeak) and maximum change in permittivity after the peak (Δϵr,max) are assessed by the MIA system and benchmarked against the corresponding parameters of a rotational thromboelastometry (ROTEM) assay. Tpeak exhibits a very strong positive correlation (r = 0.98, p < 10-6, n = 20) with the ROTEM clotting time (CT) parameter, while Δϵr,max exhibits a very strong positive correlation (r = 0.92, p < 10-6, n = 20) with the ROTEM maximum clot firmness (MCF) parameter. This work shows the potential of the MIA system as a standalone, multichannel, portable platform for comprehensive assessment of hemostasis at the point-of-care/point-of-injury (POC/POI).

Microwave dielectric properties and relaxation characteristics of Ba0.5Sr0.5TiO3 –Bi2MoO6 composite ceramics

The (1-x) Ba0.5Sr0.5TiO3-xBi2MoO6 (x = 10, 20, 30, and 40 wt%) composite ceramics were successfully synthesized through a conventional solid-phase reaction method, and the influence of A- and B- site co-doping on the dielectric properties of the BST composite ceramics was comprehensively investigated. Bi3+ ions acted as donors to replace Ba2+ and Mo6+ replaced Ti4+, producing a (BiBa∙ + MoTi∙∙)-VBa″ dipole to achieve electrovalent equilibrium. In addition, the liquid phase inhibited the growth of grains and promoted densification of the composite ceramics. The degree of B-site order was analyzed using Raman spectroscopy. With an increase in the amount of Bi2MoO6 composite, the dielectric permittivity peak broadened, the Curie temperature gradually decreased, and the tunability of the composite ceramics declined gradually. The dielectric properties of the composite ceramics benefitted from the inclusion of Bi2MoO6 and its composite effects. At the composition of x = 30 wt%, the composite ceramics exhibited excellent comprehensive properties with ε = 457 (RT), T = 14% (at 30 kV/cm), and Q = 780 (at 1148 MHz).

Stabilizing the anti-ferroelectric phase in NaO–Nb2O5–CaO–B2O3–SiO2–ZrO2 glass-ceramics using the modification of K+ ion

NaNbO3 anti-ferroelectric (AFE) material exhibits a unique and irreversible phase transition, which makes it change into ferroelectric phase and prevents its implementation in high energy storage material. In this work, we use an approach to stabilize the anti-ferroelectric phase at room temperature by the modification of K+ in NaO–Nb2O5–CaO–B2O3–SiO2–ZrO2-xK + glass-ceramics. The correlation between K+ content and anti-ferroelectric stability is studied through the X-ray diffraction, microstructure, and dielectric properties. It is found that ferroelectric phase gradually transforms to anti-ferroelectric phase first and then anti-ferroelectric phase disappears with K+ doping in glass-ceramic due to two mechanisms that the un-crystallized modifier K+ into glass network reduce the connectivity of the glass network, the activation energy needed for crystallization and the tolerance factor (t), besides overmuch K+ into NaNbO3 crystalline phase leads to the increase of tolerance factor and the production of impurity phase. The phase transition has been confirmed through the double polarization loops, AFE phase and permittivity peak. The results show that the K+ doped into NaO–Nb2O5–CaO–B2O3–SiO2–ZrO2-xK + glass system can effectively stabilize AFE phase, when x＞4%, the stability of NaNbO3 anti-ferroelectric phase will decrease and impurity phases will precipitate in glass-ceramic.

Phase transitions and microwave dielectric behaviors of the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4 ceramics

AbstractMicrowave dielectric ceramics with intrinsic low sintering temperatures are potential candidates for low temperature co‐fired ceramics technology. In the present work, the (Li0.5Y0.5)MoO4 ceramic with tetragonal scheelite structures was selected to improve microwave dielectric properties of BiVO4 ceramics. As proved by X‐ray diffraction (XRD) results, scheelite structured solid‐solution ceramics were formed with x value ≤0.1 in the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4. In situ XRD results further confirmed that the addition of (Li0.5Y0.5)MoO4 also lowered transition temperature from distorted monoclinic to tetragonal scheelite structure. When x value increased further, zircon phase was detected by XRD. Room and high‐temperature Raman spectra also supported the XRD results. Differences of thermal expansion coefficients of both monoclinic and tetragonal scheelite phases lead to an abnormality at phase transition temperature. Good microwave dielectric properties with permittivity above 70 and Qf (Q = quality factor = 1/dielectric loss and f = frequency) value above 8000 GHz were obtained in the (Bi1−xLi0.5xY0.5x)(V1−xMox)O4 solid‐solution ceramics with x value ≤0.1 sintered below 800°C. However, permittivity peak values at phase transition temperatures lead to large positive or negative temperature coefficient of resonant frequency, and this needs to be modified via composite technologies in the future.

Anhydrous copper tellurite disulfate Cu3TeO3(SO4)2 featuring the coexistence of spin singlets and a long-range antiferromagnetic order.

Anhydrous copper tellurite sulfate, Cu3TeO3(SO4)2, has been synthesized via vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization M, magnetic susceptibility χ, specific heat Cp and X-band electron spin resonance, a long-range antiferromagnetic order at TN = 13 K and an H-T magnetic phase diagram have been established. One-third of Cu2+ ions were found to form magnetically silent dimers. A peak in dielectric permittivity ε, which accompanies the Néel order, allows considering Cu3TeO3(SO4)2 as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters.

Defects minimisation promoted by lead-volatility in (Pb,La)(Zr,Ti)O3 ferroelectric ceramics

La-modified PbZrTiO3 ferroelectric ceramics with Pb0.92La0.08(Zr0.686Ti0.294)O3 nominal composition were obtained via the conventional solid-state reaction method, by considering different PbO excess (5, 10 and 15 mol %). The structural properties, were investigated from X-ray diffraction (XRD) and Raman Spectroscopy techniques, both at room temperature. Results confirmed the formation of the perovskite structure with rhombohedral symmetry (R3m space-group) for all the samples. The dielectric properties were also investigated, from the temperature dependence of the dielectric response, and results revealed the characteristic response of ferroelectric materials for all the compositions. The obtained very broad peak in the maximum dielectric permittivity, around Tm (~107°C), suggests the diffuse character of the ferroelectric-paraelectric phase transition.

Sub-switching domain effect for analysis the non-linear dielectric behavior of (K0.49 Na0.49Li0.02) (Nb0.98Sb0.02)O3 ceramic based on Rayleigh model

The solid-state sintering technique has been implemented to synthesize (K0.5Na0.5NbO3)-0.02(LiSbO3) (KNN-LS) Pb-free ceramic. The crystal structure, dielectric and ferroelectric properties of the prepared material were investigated. Pure orthorhombic perovskite phase [I(220)/I(002) = 1.68] with Amm2 space group has been detected at room temperature for sintered ceramic. Two anomalous permittivity peaks corresponding to orthorhombic–tetragonal (O–T) phase transition at T = 175 °C and tetragonal–cubic (T–C) phase transition at T = 355 °C have been observed. At polymorphic phase transition, the Rayleigh model shown the extrinsic contributions caused by domain wall motion is about 80%, while the intrinsic contribution attributed to the lattice distortion is about 20%. Ferroelectric properties were investigated in a wide range of temperatures (RT-225)°C. The results shown a conductive material at high temperature due to the higher cation disorder and leakage current above PPT. The present results are interested for understanding the mechanism of t permittivity–temperature behavior of KNN-doped LS ions based on Rayleigh model. The large remnant polarization and low coercive field below PPT make the material a suitable candidate for energy storage application.

Enhancement of Nonlinear Dielectric Properties in BiFeO3-BaTiO3 Ceramics by Nb-Doping.

BiFeO3–BaTiO3 (BF–BT) ceramics exhibit great potential for diverse applications in high temperature piezoelectric transducers, temperature-stable dielectrics and pulsed-power capacitors. Further optimization of functional properties for different types of applications can be achieved by modification of processing parameters or chemical composition. In the present work, the influence of pentavalent niobium substitution for trivalent ferric ions on the structure, microstructure and dielectric properties of 0.7BF–0.3BT ceramics was investigated systematically. Doping with niobium led to incremental reductions in grain size (from 7.0 to 1.3 µm) and suppression of long-range ferroelectric ordering. It was found that core-shell type microstructural features became more prominent as the Nb concentration increased, which were correlated with the formation of distinct peaks in the dielectric permittivity–temperature relationship, at ~470 and 600 °C, which were attributed to the BT-rich shell and BF-rich core regions, respectively. Nb-doping of BF–BT ceramics yielded reduced electronic conductivity and dielectric loss, improved electrical breakdown strength and enhanced dielectric energy storage characteristics. These effects are attributed to the charge compensation of pentavalent Nb donor defects by bismuth vacancies, which suppresses the formation of oxygen vacancies and the associated electron hole conduction mechanism. The relatively high recoverable energy density (Wrec = 2.01 J cm−3) and energy storage efficiency (η = 68%) of the 0.7BiFeO3–0.3BaTiO3 binary system were achieved at 75 °C under an electric field of 15 kV mm−1. This material demonstrates the greatest potential for applications in energy storage capacitors and temperature-stable dielectrics.

Exploring the energy storage density in 60Bi2O3–10SrO-30Fe2O3 lead-free relaxor glass for designing energy storage devices

Strontium doped glass was synthesized by the conventional melt-quenching technique. Systematically measured dielectric properties revealed relaxor ferroelectric-like behavior in a broad range of frequency and temperature. The glassy nature of the present sample was investigated by X-ray diffraction (XRD) measurements. glass transition temperature, crystallization temperatures and melting temperature are determined by differential thermal analysis (DTA). The low frequency Raman spectra displays a Boson peak at 72 cm−1, which confirms polar clusters (PCs) formation. The present sample depicts a wide as well as diffuse peak of dielectric permittivity ε'(ω) and tangent loss tan δ. wide as well as diffuse peak shifted to the higher temperatures (from 538 K to 553 K), a typical relaxor behavior is indicated by this type of diffuse transition. The presence of polar clusters (PCs) imbedded in the glass matrix indicates the presence of relaxor ferroelectric (RFE) behavior in this glass. The measured energy storage density of the strontium doped glass was 4 mJ.cm−3 with efficiency of 70% under an applied electric field of 17 kV.cm−1 at room temperature. Magnetic properties via vibrating-sample magnetometer (VSM) show a typical anti-ferromagnetic behavior. These results depict that the present glass can be regarded a promising candidate for designing energy storage devices.

Superior thermal stability and energy storage properties of (1-x)Na0.3Bi0.3Ba0.04Sr0.36TiO3-xZnTa2O6 lead-free ceramic

It is challengeable to winden the operating temperature and optimize the energy storage properties of ceramic capacitors in power system applications. Here, the lead-free (1-x) Na0.3Bi0.3Ba0.04Sr0.36TiO3-xZnTa2O6 (BNBST-xZT) ceramics were designed. The introduction of ZT into BNBST reduced the temperature of permittivity peak of BNBST ceramic, which guaranteed the superior thermal stability following X7R specification. Due to the compositional disorder and structural distortion, the ferroelectric order of BNBST was broken, mitigating polarization saturation. The high recoverable energy density (Wrec = 3.06 J/cm3) with high efficiency (η = 92.91%) was achieved under 270 kV/cm. The fast discharge speed (t0.9 ~ 170 ns), large power density (PD = 60.46 MW/cm3), thermal stability, and superior cycle stability were evaluated to illustrate its promising practical prospect using in pulsed power capacitor devices.

Excellent thermal stability and energy storage properties of lead‐free Bi0.5Na0.5TiO3‐based ceramic

AbstractThe ceramic capacitors with excellent energy storage properties and wide operating temperature are the main challenges in power system applications. Here, the lead‐free (1‐x)Bi0.5Na0.5TiO3‐xCaTiO3 (abbreviated as BNT‐xCT) ceramics were synthesized through solid‐state reaction method. The introduction of CT reduced the temperature of permittivity peak of BNT ceramic, guaranteeing excellent thermal stability over a wide temperature range of −100 ∼ 136°C. Meanwhile, the long‐range order structure of BNT was destructed by structural distortion, and the relaxor behavior was enhanced after doping CT. Moreover, the direct current breakdown strength was improved from 203 to 455 kV/cm, and the high recoverable energy density (Wrec ∼ 2.74 J/cm3) with high efficiency (η ∼ 91%) was achieved for BNT‐0.25CT ceramic, along with a fast discharge speed (t0.9 ∼ 110 ns) superior cycle stability and thermal stability. Those properties enabled a promising practical prospect of BNT‐CT ceramics.

Enhancement of energy storage performance in lead-free barium titanate-based relaxor ferroelectrics through a synergistic two-step strategy design

Dielectric capacitors are widely used because of their advanced performance, including superior power density and high charge–discharge speed. Nevertheless, limitations in energy-storage density (Wrec), efficiency (η) and thermal stability hinder their practical application. Herein, these concerns are addressed using a synergistic two-step strategy of designing the composition of Bi(Zn2/3Nb1/3)O3 and optimizing the preparation for viscous polymer processing (VPP), thus achieving domain engineering, enhanced relaxor behavior, and improved breakdown strength (Eb) in (Ba0.8Sr0.2)TiO3-based ceramics. The broadening of the permittivity peak and highly dynamic polar nanoregions (PNRs) are correlated to expected relaxation characteristics, as indicated by the brightness of atomic position and calculated spontaneous polarization vectors determined through transmission electron microscopy. The relatively small grain size and increased band gap, verified through scanning electron microscopy and ultraviolet − visible spectrophotometry, contribute to the Eb. A prominent Wrec of 5.16 J/cm3 under 540 kV/cm and excellent temperature stability (Wrec = 3.6 J/cm3, η = 92.8%, 20–120 °C) are achieved in 0.91(Ba0.8Sr0.2)TiO3 − 0.09Bi(Zn2/3Nb1/3)O3 ceramics formed by VPP (BZN9VPP). The material possesses an exceptional current density of 647.56 A/cm2, a power density of 113.32 MW/cm3, and a rapid discharge speed of < 60 ns. The comprehensive outstanding performance supports the great potential of this sample for application in pulsed power capacitors.

Prepreg age monitoring and qualitative prediction of mechanical performance of composite using dielectric state variables

The aviation and automobile industries have recently depended on thermoset epoxy-based prepreg as a raw material for manufacturing composites. Since prepregs have a limited out-life (i.e., the maximum storing time allowed at room temperature), they must be stored in refrigerators at low temperatures. If not maintained, they can often adversely affect the desired quality of the final product. Prepregs are often discarded once the prepreg out-life ends, leading to a loss of millions of dollars and a detrimental impact on the environment. Therefore, it is necessary to develop a simple method to monitor prepreg aging/degradation in order to ensure its usability or repurpose prepreg usage. In this study, we used broadband dielectric spectroscopy to monitor the degradation state of the glass fiber/epoxy prepreg sample stored at room temperature, and the data has been used to predict the mechanical performance of the final manufactured composite part. The frequency-based nondestructive dielectric measuring technique was used to calculate the dielectric strength and relaxation time of the prepregs. The dielectric strength decreased and relaxation time increased with aging, allowing the aging progression to be captured. Furthermore, with aging, the real permittivity value changes to a lower value and the relaxation peak in imaginary permittivity with respect to frequency shifts to a lower frequency. The physics behind this dielectric measurement method has been understood in the context of analyzing the prepreg’s cure kinetics parameters, which has been investigated using differential scanning calorimetry. Overall, this simple dielectric-based monitoring technology will provide confidence in the future use of degraded or out-of-life raw material systems for manufacturing.

Dielectric relaxation induced by oxygen vacancies in Na0.5Bi0.5TiO3 ceramics

Dielectric permittivity was studied in ceramics of relaxor ferroelectric bismuth-sodium titanate Na0.5Bi0.5TiO3. The measurements were performed on as sintered and heat treated in vacuum samples. The diffuse dielectric anomalies associated with the structural phase transitions were observed in as sintered samples. The intense peak of permittivity (εmax ∼ 104) appeared after heat treating in vacuum. The anomaly of ε(T) was contributed by slow polarization processes (f &lt; 10 kHz) and was non-stable, vanishing on heating in air up to ∼ 800 K. Temperature and frequency dependencies of ε were described by using Cole-Cole model with accounting thermally stimulated decay of the non-stable polarization. It is supposed that the dielectric anomaly is determined by space charge polarization mechanism. Oxygen vacancies VO•• and electrons localized on titanium ions Ti'Ti are assumed to be responsible for the phenomenon observed.

Doping level effects in Gd/Cr co-doped Bi3TiNbO9 Aurivillius-type ceramics with improved electrical properties

In this work, different amount of Cr2O3 (x = 0–0.3 wt%) as dopant were doped into the Aurivillius-type compound Bi2.8Gd0.2TiNbO9 (BGTN), such a kind of Gd/Cr co-doped Bi3TiNbO9 ceramics with improved electrical properties were synthesized by the convenient solid-state reaction route. The substitution of Cr3+ for Ti4+ at B-site induced the lattice distortion of pseduo-perovskite layer. Fewer Cr2O3 dopant (x<0.2) resulted in the grain refinement of ceramics. After Cr2O3 was added into BGTN, TC decreased to the vicinity of 908 °C. Below TC, the relaxed dielectric response resulted from charge carriers hopping induced another board dielectric permittivity peak, whose starting temperature shifts toward lower side gradually with increase of x. The values of Eacon calculated from the Arrhenius relationship between conductivity and temperature indicated the intrinsic conduction at high temperature is dominated by the long-range migration of doubly ionized oxygen vacancies. Moderate Cr2O3 dopant (x = 0.1–0.25) are conducive to the enhancement of piezoelectric property and thermal stability. The sample with x = 0.2 achieved both a high TC∼903 °C and a high d33∼18 pC/N at the same time. Also, its d33 can retain 80% of the initial value after the sample was annealed at 800 °C for 4 h.

Structure and local structure investigation of (0.85-x)BaTiO3-0.15BiFeO3-xKVO3 system linked to electrical properties

In this work, the composition of (0.85-x)BaTiO3–0.15BiFeO3–xKVO3 (TFVx) was investigated. The sintered sample behaves tetragonal perovskite ABO3 structure, defects, and a trace secondary phase of Ba3(VO4). The X-ray Absorption Near Edge Spectroscopy (XANES) analysis on the Fe K-edge TFVx sample determined the oxidation state of Fe, it is a mixture of 3+ and 4+, while the Extended X-Ray Absorption Fine Structure (EXAFS) revealed a local distortion of octahedron BO6. The Arrhenius plot of the ln σ vs. 1/T showing n-type semiconductor, the conductivity behavior indicates it presents the small polaron hopping, Schottky defect, and oxygen vacancy VO••that contribute to the conductivity. The relative permittivity (εr) displays two maxima related to Curie temperature of the matrix BaTiO3 and the defective lattice producing diffuse transition that intervene permittivity. Increasing the frequency causes the peak permittivity and the dielectric loss (tanδ) shift towards higher temperatures. These findings suggest the sample delivering relaxor behavior.