Thermally Stimulated Depolarization Current Research Articles

Oxygen vacancy migration and impact on high voltage DC polarization in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3

AbstractElectrical polarization and defect transport are examined in 0.8BaTiO3–0.2BiZn0.5Ti0.5O3, an attractive capacitor material for high power electronics. Oxygen vacancies are suggested to be the majority charge carrier at or below 250°C with a grain conduction hopping activation energy of 0.97 eV and 0.92 eV for thermally stimulated depolarization current (TSDC) and impedance spectroscopy measurements, respectively. At higher temperature, thermally generated electronic conduction with an activation energy of 1.6 eV is dominant. Significant oxygen vacancy concentration is indicated (up to ∼1%) due to cation vacancy formation (i.e., acceptor defects) from observed Bi (and likely Zn) volatility. Oxygen vacancy diffusivity is estimated to be 10−12.8 cm2/s at 250°C. Low diffusivity and high activation energies are indicative of significant defect interactions. Dipolar oxygen vacancy defects are also indicated, with an activation energy of 0.59 eV from TSDC measurements. The large oxygen vacancy content leads to a short lifetime during high voltage (30 kV/cm), high temperature (250°C) direct current (DC) electrical measurements.

Effect of A/B ratio on the dielectric properties and insulation resistance of barium titanate sintered in a reducing atmosphere

The effect of the A/B ratio on the dielectric properties and insulation resistance of barium titanate (BaTiO3) sintered in a reducing atmosphere was investigated in this study. The increased demand for high capacitance, miniaturized, and reliable base metal electrode multilayer ceramic capacitors (BME MLCCs) has emphasized improving insulation properties. This study added Y2O3, MgO, Mn2O3, and SiO2 to tailor the barium titanate properties. We investigated how changes in the A/B ratio affect the microstructure, defect chemistry, and Y3+ ion occupation in BaTiO3, affecting dielectric properties and insulation resistance. It was observed that the activation energies for grain and grain boundary conductivity are dominated by oxygen vacancy and (VBa″−VO··) defect pair, respectively. The Ti3+ and oxygen vacancy concentrations were directly proportional to the room and high-temperature resistivities, respectively. The sample with an A/B ratio of 1.002 had the lowest oxygen vacancy and Ti3+ ratio, resulting in a higher resistance and lower thermally stimulated depolarization current (TSDC).

Role of Mixed Oxidant and Controlled Oxygen Partial Pressure Heat Treatment to Regulate the Dielectric Properties and Resistivity of SrTiO3-based CP Ceramics

Sr0.99La0.01TiO3 (SLT10) colossal permittivity (CP) ceramic materials were synthesized using solid phase method and secondary heat treated using mixed oxidant 35%Bi2O3-10%Al2O3-20%MgO-25%CuO-10%SiO2 oxidant. The heat treatment atmospheres were chosen as O2, air, and Ar to correspond to different oxygen partial pressures. The dielectric properties of the Sr0.99La0.01TiO3-Percolated (SLT10-P) ceramics were investigated, and the contribution of the oxidant to the resistivity enhancement was verified by complex impedance spectroscopy and DC resistivity tests. Excellent dielectric properties were obtained for SLT10-P Air ceramic sample (16543 for dielectric permittivity and 0.016 for loss tangent), and the resistivity was increased from 2.13×108 Ω·cm (SLT10) to 1.23×1011 Ω·cm (SLT10-P Air). The resistance degradation mechanism of SLT10-P ceramics and oxygen vacancy migration in the process of resistance degradation were studied by using resistance monitoring device and thermally stimulated depolarization currents (TSDC) test. The introduction of oxidant optimizes the temperature stability and resistivity of SLT10 ceramics, but it will lead to the decrease of dielectric permittivity. The atmosphere of heat treatment changed the concentration of oxygen vacancy in ceramics. When SLT10-P O2 was treated in O2 atmosphere, the concentration of oxygen vacancy in ceramics decreased, which led to the decrease of dielectric permittivity and the increase of grain boundary resistance. For SLT10-P Ar ceramic, more oxygen vacancies and free electrons are induced by low oxygen partial pressure heat treatment, which enhances the dipole effect of electron pinning defects and leads to colossal dielectric permittivity, but high concentration of oxygen vacancies will affect the resistance decline. In SLT10-P Air ceramic, the coexistence of colossal permittivity and low loss tangent and high resistance is realized.

Modulated electrical performance of cross-linked polyethylene by grafted charge-attracting molecules for high voltage direct current cable insulation

In order to figure out the effects of charge-attracting molecules on the direct current electrical performance of crosslinked polyethylene (XLPE), the molecules with different structures and functional groups were grafted onto XLPE, and their space charge, volume resistivity and thermal stimulated depolarization current were investigated. Based on density function theory, the trap distribution and charge-attracting properties of the grafted XLPE were calculated. For the charge-attracting groups, the results indicate that with the grafted of trap molecules containing polar groups CO and N-H, the electron and hole traps are introduced and the ability of attracting negative charges and positive charges are extremely improved, respectively, resulting in the enhanced space charge hindering and suppressed resistivity. The benzene ring can form both electron and hole traps with relatively shallower energy level, and results in an improved space charge dissipation and decreased resistivity. For the combination of charge-attracting groups, the continuous arrangement of homogeneous charge-attracting groups can achieve an enhanced modification effect, and heterogeneous charge-attracting groups will attenuate the modification ability. For the molecule structure, the grafting of compact cyclic molecular can affect the electrostatic potential distribution on XLPE’s chain, and exhibits a stronger modification effect.

Synthesis, X-ray diffraction and dielectric studies of the ceramic samples (1−x)BaTiO3⋅xPbFe2/3W1/3O3 (0≤x≤1) system

Ceramic samples of the ([Formula: see text])BaTiO3⋅xPbFe[Formula: see text]W[Formula: see text]O3, [Formula: see text] (([Formula: see text])BT⋅xPFW) system were synthesized by solid-state reactions method. The samples were characterized by X-ray diffraction (XRD) and dielectric studies, as well as by the measurements of the thermally stimulated depolarization currents (TSDC). It was found that the predominant phase in the samples is presented by the (Ba[Formula: see text]Pbx)(Ti[Formula: see text]Fe[Formula: see text]W[Formula: see text])O3 solid solutions with a perovskite structure, herewith the samples with [Formula: see text] are practically single-phase, and with [Formula: see text] contain the impurity phase BaWO4 (up to 15 mass.% at [Formula: see text]–0.90). Information has been obtained about the changes in the structural and dielectric characteristics of the solid solutions with the change of their composition. It is established that the solid solutions crystal lattice symmetry at 296 K changes from tetragonal at [Formula: see text] to cubic at [Formula: see text]. An increase in the PFW content in solid solutions causes a gradual change in their properties from ferroelectric at [Formula: see text] to relaxor ferroelectric at [Formula: see text], and then to properties similar to those of the dipole glass with weak or zero correlation between dipoles at [Formula: see text]. The addition of BT to PFW leads to rather quick degradation of the relaxor ferroelectric properties of PFW in the region [Formula: see text]–1.0.

ВЛИЯНИЕ ТОЛЩИНЫ ПЛЕНОК ПОЛИДИФЕНИЛЕНФТАЛИДА НА СПЕКТР ТОКОВ ДЕПОЛЯРИЗАЦИИ МНОГОСЛОЙНЫХ СТРУКТУР

The depolarization currents of multilayer polymer films of polydiphenylene phthalide were measured using the thermally stimulated depolarization (TSD) method in the range from 170 to 400 K. The solution concentration was 2.5 and 5 wt.%. Each layer of polymer film was pre-dried at room temperature, then annealed in an oven. The number of layers of polymer film was 1, 2, 3 and 7 layers for 2.5 wt.%. and 1, 2, 3, 5 and 7 layers for 5 wt.%. The polarizing electric field strength was 2.5 × 105 V/cm. The rate of temperature change was 5 K/min. Based on experimental data, the dependence of the temperature of the position of the maximum peak of the depolarization current, the maximum values of the peaks of the depolarization currents, the values of the released charge and the activation energy of relaxation processes on the number of layers of the polymer film is shown. The temperature dependences of depolarization currents revealed two regions for a solution concentration of 2.5 wt.%. and one area for 5 wt.%. The first region is interpreted in the dipole charge approximation. The second region is explained by the presence of a wide distribution of traps occupied by injected charges. Interlayer polarization is observed in inhomogeneous dielectrics and is caused by differences in the electrical conductivity and dielectric constant of individual particles (or microparticles) of the dielectric. In such dielectrics, when an electric field is applied at the interface between its various components, charge will accumulate, which is equivalent to the creation of polarization. The results for the temperature dependences of the TSD currents of the samples showed that the total accumulated charge in the volume increases as the number of polymer layers increases. The reason for such a high concentration of trapped charges is most likely due to the presence of a wide distribution of traps occupied by injected charges. Moreover, the magnitude of the released charge is greater for samples prepared from a polymer solution with 2.5 wt. % This effect depends on the thickness of the polymer films. Namely, the thinner the films, the more charged particles penetrate the interface between the films.

Effects of Zr4+ and Hf4+ substitution on the structure and dielectric response of Ba4Sm9.33Ti18O54 ceramics

Microwave dielectric ceramics with high relative permittivity (εr) are commonly used for the miniaturation of microwave devices. The dielectric loss mechanism of microwave dielectric ceramics, as well as the property modification, has been a concerned topic among scholars. Herein, the lattice structure, defects, and broadband dielectric response of Zr4+ and Hf4+ substituted Ba4Sm9.33Ti18O54 (BST) ceramics are systematically examined. The negative temperature coefficient of resonant frequency (τf) of BST ceramics can be tuned to near zero via ion substitution, owing to the Sm2Ti2O7 second phase with a large positive τf. Optimal microwave dielectric properties of εr = 81.3, Q × f = 10,800 GHz, and τf = −4.6 ppm/°C are achieved. The lattice vibration behavior and defect concentration are analyzed by Raman spectra and thermally stimulated depolarization currents (TSDC), respectively. The increasing volume of the unit cell and TiO6 octahedra, which is because of the large-radius substitution ions, leads to an increase in lattice vibration damping factor and the generation of more oxygen vacancies (VO∙∙). Therefore, the dielectric losses in the microwave and terahertz (THz) bands increase after substitution. Meanwhile, the low-frequency dielectric losses at high temperatures also increase due to the weak restraint of carriers by the lattice. The broadband loss mechanism of Zr4+ and Hf4+ substituted BST ceramics related to lattice vibration and defects might be referenced for developing low-loss dielectric ceramics.

Effect of Li1.3Al0.3Ti1.7(PO4)3 on semiconductive composites: Positive temperature coefficient (PTC) performance and inhibition of space charge injection

The semiconductive layer located between the core and insulation layer of a high-voltage DC (HVDC) cable can inhibit the accumulation of space charge in the insulation layer. This helps increasing the electric field inside the cable, thus improving the stress distribution of the electric field on the inner and outer surfaces of the insulation layer and the electrical strength of the cable. An inevitable positive temperature coefficient effect (PTC) in the semiconductor layer leads to aging failure of the insulation layer. To improve this phenomenon, the semiconductive shielding layer was modified for suppressing its PTC effect and reducing the space charge injection into the insulation layer. Li1.3Al0.3Ti1.7(PO4)3(LATP) was prepared via a solid-phase reaction and added to a composite consisting of carbon black (CB), ethylene vinyl acetate copolymer (EVA), and low-density polyethylene (LDPE). Resistivity, thermally stimulated depolarization current (TSDC), and pulsed electroacoustic (PEA) measurements were performed on the modified sample. The results showed that when the LATP content was 4 wt%, the modification effect of the semiconductive shielding layer was most effective, the PTC effect was reduced by 11%, and the space charge injection into the insulating layer was improved significantly.

Electrical-Tree Resistant Characteristics of SEBS and Nano-SiO2 Modified Polypropylene Composites

Polypropylene (PP) composite materials with both high mechanical toughness and electrical insulation performance are prepared by incorporating styrene-ethylene/butylene-styrene (SEBS) block copolymer as a toughening agent and nanoscale silica (SiO2) as a inorganic modifier to enhance electrical-tree and breakdown resistances. The effects and mechanisms of SEBS toughening agent and SiO2 nanofiller on the thermal-mechanical properties and electrical insulation performances of PP material are investigated through the mechanical tests as well as the accelerated electrical-tree aging and alternative current (AC) breakdown experiments. The elastic modulus of SiO2/SEBS/PP composite is slightly lower than that of pure PP material, while the thermal elongation rate remains superior to cross-linked polyethylene (XLPE), which is competent in mechanical performances for main insulation materials in high-voltage cables. The addition of styrene-ethylene/butylene-styrene (SEBS) facilitates electrical-tree growth in PP matrix and thus leads to the reduction in dielectric breakdown strength of PP material. In contrast, the incorporation of nano-SiO2 can effectively improve the electrical-tree resistance and dielectric breakdown strength of PP material, making the SiO2/SEBS/PP composite a promising candidate for high-voltage cable insulation. The tests and analyses of thermal stimulated depolarization current (TSDC) reveal that the SEBS toughing additive introduces the shallow charge traps in PP matrix, making it easier for the trapped charges to transition into charge carriers, thus leading to a considerable decrease in electrical-tree resistance and insulation strength of PP material. Meanwhile, the SiO2 nanofiller can introduce deeper charge traps into PP matrix than the structural-defect intrinsic charge traps, resulting in a significant amelioration in the electrical-tree resistant and insulation performances for SEBS/PP composite. The present study demonstrates that SiO2/SEBS/PP composite possesses sufficiently high electrical-tree resistance and dielectric breakdown strength as well as suitable thermal-mechanical properties, offering a potential application in main insulation of high-voltage cables and providing an effective pathway for developing novel recyclable AC high-voltage cables.

Efficient single-crystal 4-N,N-dimethylamino-4-N-methyl-stilbazolium tosylate (DAST) on the optical, piezoelectric coefficient and structure of P(VDF-HFP) copolymer for energy conversion systems

Poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) doped with 4-N,N-dimethylamino-4-N-methyl-stilbazolium tosylate (DAST) composites with various concentrations of DAST dye is prepared using the casting method. The crystal structure and optical properties of the pure and P(VDF-HFP)/DAST composites with various contents of DAST dye are investigated using various techniques such as UV–Vis spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and polarized optical microscopy (POM). The analysis of XRD data and FTIR spectra revealed that the β-fraction has been improved in the composite samples with increasing the content of DAST dye. Analysis of UV spectra displayed that the optical band gap of P(VDF-HFP) pure copolymer is 5.41 eV and has been reduced to be 3.75 eV for P(VDF-HFP)/10 wt% DAST that will be suitable for efficient systems of energy conversion and multijunction-based layer solar cells. Also, it is found that the nonlinear and linear optical parameters of the composite samples are DAST dye-dependent. Thermally stimulated depolarization current (TSDC) technique has been applied to investigate the dipolar and space charge relaxations of the composites. Moreover, it is observed that the pyroelectricity and piezoelectricity are enhanced with increasing the content of DAST dye. The highest content of the DAST dye showed maximum values of the pyroelectric and the piezoelectric coefficients of ~ 4 × 10–5 C/m2 K and ~ 34 pC/N at stress of 6.27 × 105 Pa, respectively. Our results of the polymer/dye composites give an opportunity of a promising material for flexible piezoelectricity devices used in many potential applications and energy harvesting systems.

Optimizing dielectric strength and viscosity of synthetic ester with wide bandgap nano-additives

This study explores the potential of insulating oil-based nanofluids as a promising alternative to traditional insulating oils. Specifically, we employ a thermally stimulated depolarization current (TSDC) approach to characterize the effect of trapped charges on the dielectric strength of synthetic ester (SE) based oils (bare SE, SE/Co3O4, and SE/Al2O3). The TSDC findings indicate that nanofluids exhibit higher current density peaks and trap energy levels than bare oil. Nonetheless, the AC breakdown voltage (BDV) of SE oils is significantly enhanced when nanoparticles are well-dispersed. The wide bandgap of Co3O4 and Al2O3 nanoparticles might be responsible for the increase in trap levels, enabling nanofluids to withstand higher AC electric field than pure oils. Additionally, we conduct statistical analyses of the AC BDV values of SE-based oils. Lastly, we find that nanofluids have a lower kinematic viscosity than bare oil.

Dipole behavior in thin film heterostructure composed of Er-doped SnO2 and GaAs: Influence of polarization bias, temperature and stray light

The heterostructure system GaAs/SnO2 is built by resistive evaporation of Er-doped SnO2 powder on the top of GaAs semi-insulating substrate. The SnO2 powder comes from the drying of SnO2 sol-gel solution. The possible formation of dipoles in this heterostructure is investigated by the thermally stimulated depolarization current (TSDC) technique, and the possibilities for dipole formation are explored, such as the EL2 defect in the GaAs side, oxygen vacancies and Er ions in the SnO2 layer. The dipole relaxation activation energies are found in the range 0.2 eV to 0.3 eV, in good agreement with the ionization energies of these defects. The main TSDC bands: 213 meV with peak of −298 pA, for positive bias, and 218 meV with peak of 128 pA for negative bias, are modified by stray (room) light, which may correspond to the second ionization level of oxygen vacancies in SnO2, which are excited by the room lights and do not return to the original orientation.

Defect-related broadband dielectric loss mechanisms of Na1/2Sm1/2Ti1–z(Al1/2Nb1/2)zO3 ceramics

Dielectric ceramics with low dielectric loss in the microwave bands are key materials used in fifth/sixth-generation (5G/6G) telecommunication. Exploring the defect behavior and the broadband dielectric response of ceramics is helpful to understand the loss mechanism and develop novel low-loss microwave dielectric ceramics. In this work, Al/Nb was co-substituted for Ti4+ in Na1/2Sm1/2TiO3 (NST) ceramics with a perovskite structure, and the low frequency, microwave and terahertz (THz) dielectric responses were investigated. In different frequency bands, the variations of dielectric loss with substitution amount are inconsistent. The Al/Nb-substitution increases the dielectric loss in the low frequency and microwave bands, while the dielectric loss in the THz band decreases. The changes in dielectric loss are closely related to the lattice defects in Na1/2Sm1/2Ti1–z(Al1/2Nb1/2)zO3 (NST-zAN, 0 ≤ z ≤ 0.1) ceramics, which are studied by thermally stimulated depolarization current (TSDC) technique. The dielectric relaxation of the defects including oxygen vacancies (VO··) and defect dipoles leads to the dielectric loss in the low-frequency and microwave bands. The dielectric loss in the THz band is mainly affected by the damping of lattice vibration, which is associate with the defect concentration. This work might provide a considerable reference for the development of low-loss dielectric materials.

Molecular Layer Deposition of Polyurea on Silica Nanoparticles and Its Application in Dielectric Nanocomposites.

Polymer nanocomposites (NCs) offer outstanding potential for dielectric applications including insulation materials. The large interfacial area introduced by the nanoscale fillers plays a major role in improving the dielectric properties of NCs. Therefore, an effort to tailor the properties of these interfaces can lead to substantial improvement of the material's macroscopic dielectric response. Grafting electrically active functional groups to the surface of nanoparticles (NPs) in a controlled manner can yield reproducible alterations in charge trapping and transport as well as space charge phenomena in nanodielectrics. In the present study, fumed silica NPs are surface modified with polyurea from phenyl diisocyanate (PDIC) and ethylenediamine (ED) via molecular layer deposition (MLD) in a fluidized bed. The modified NPs are then incorporated into a polymer blend based on polypropylene (PP)/ethylene-octene-copolymer (EOC), and their morphological and dielectric properties are investigated. We demonstrate the alterations in the electronic structure of silica upon depositing urea units using density functional theory (DFT) calculations. Subsequently, the effect of urea functionalization on the dielectric properties of NCs is studied using thermally stimulated depolarization current (TSDC) and broadband dielectric spectroscopy (BDS) methods. The DFT calculations reveal the contribution of both shallow and deep traps upon deposition of urea units onto the NPs. It could be concluded that the deposition of polyurea on NPs results in a bi-modal distribution of trap depths that are related to each monomer in the urea units and can lead to a reduction of space charge formation at filler-polymer interfaces. MLD offers a promising tool for tailoring the interfacial interactions in dielectric NCs.

Defect evolution and effect on structure and electric properties of A/B site Sm doped BaTiO3 sintered in different atmospheres

BaTiO3 ceramics doped with different contents of Sm (0.5-7 mol%) are prepared by a homogeneous precipitation method and sintered in air (A-xSm) and reducing (R-xSm) atmosphere respectively. With the increase of doping amount, the phase structure of Sm-doped BaTiO3 ceramics gradually changes from tetragonal phase to cubic phase, and the cubic phase is stronger in R-xSm. In the air atmosphere, Sm ions preferentially replace Ba sites as donors at low doping concentration, which is easy to convert Ti4+ ions into Ti3+ ions, resulting high dielectric constant (>104) and semiconductor like properties. As the doping amount increases, Sm ions start to replace Ti sites as acceptors to generate oxygen vacancies, which capture the electrons generated by donor doping, thus decreasing the percentage of Ti3+ ions. As a result, the dielectric loss and permittivity are decreased, and the electrical insulation properties of A-xSm ceramics are gradually improved. However, in the reducing atmosphere, oxygen atoms in the lattice are easy to escape, resulting in many oxygen vacancies and free electrons. The increase of oxygen vacancy inhibits the substitution of Sm ion to Ti site, and the free electron leads to the increase the percentage of Ti3+ ions and R-xSm ceramics exhibit semiconductor like properties. Thermally stimulated depolarization currents (TSDC) testing verified that oxygen vacancies of A-xSm ceramics mainly capture space charges, and a small part of oxygen vacancies form defective dipoles [2SmTi′−VO..]. The complex impedance test shows that the change of resistivity of A-xSm ceramics is mainly closed to the influence of Sm doping on the grain not grain boundary of BaTiO3 ceramic.

Dielectric and anti-reduction properties of BaTiO3-based ceramics for MLCC application

BaTiO3 ceramics doped with different contents of Co2O3(abbreviated as (1-x) BT-xCo2O3) and (1-x) BaTiO3-xBiCoO3(abbreviated as (1-x) BT-xBC) ceramics were prepared via conventional solid-state process and sintered in reducing atmosphere. The main crystal phase of both ceramic samples was characterized by X-ray diffraction (XRD), which was perovskite structure. Compared with (1-x) BT-xCo2O3, (1-x) BT-xBC ceramic samples were dense with uniform microstructure confirmed by scanning electron microscopy (SEM). The 0.95BT-0.05BC ceramics had good dielectric properties, with ε25°C = 2670, tanδ = 0.012, and resistivity was 1.71 × 1011 Ω cm at 25°C, meeting the X7S standard for multilayer ceramic capacitor (MLCC) applications. The mechanism of improved anti-reduction property of (1-x) BT-xBC ceramics was studied by X-ray photoelectron spectroscopy (XPS) and thermally stimulated depolarization current (TSDC) techniques. The XPS results showed that there were two valence states of Co in 0.95BT-0.05BC and 0.95BT-0.05Co2O3 ceramics, indicating that the introduction of Co can improve anti-reduction property of BT-based ceramics. The TSDC revealed the formation of defect dipoles [2CoTi’−Vo▪▪], which was considered to be the cause for the improvement in anti-reduction property.

Review of the thermally stimulated depolarization current (TSDC) technique for characterizing dielectric materials

Review of the thermally stimulated depolarization current (TSDC) technique for characterizing dielectric materials

Piezoelectric properties and depolarization characteristics of BNKLT-0.15/0.075 ceramics doped with different ions

Ternary system Bi0.5(Na0.775K0.15Li0.075)0.5TiO3 (BNKLT-0.15/0.075) ceramics doped with Mn2+, Fe3+, Sm3+ ions have been successfully prepared using the high temperature sintering method. The phase structure, piezoelectric properties and depolarization characteristics of the ceramics have been investigated. It is found that Mn2+, Fe3+ ions replace Ti4+ ions and Sm3+ ions replace Bi3+ ions in the BNKLT-0.15/0.075 ceramics. 0.3 mol% Mn2+ doping has a ‘hard’ effect in BNKLT-0.15/0.075 ceramics like it plays the role in lead-contained Pb(Ti,Zr)O3 ferroelectric ceramics. Fe3+ can significantly improve the d33 and kp of the ceramics, while maintaining a slight increment of Qm. However, Sm3+ doping decreases the d33 and kp of the ceramics. The distinct difference of the doping effects on the electrical properties of the ceramics is tightly related to the depolarization process of the ceramics. It is found the thermally stimulated depolarization current (TSDC) of the prepared ceramics have two peaks: one is caused by the disintegration of long-range ferroelectric order into polar nanoregions at Td, and the other peak is induced by the phase transition from R3c to P4bm at Tc-d. The depolarization process of the ceramics has been discussed basing on the TSDC, dielectric characterization and in-situ XRD measurement of the ceramics.

Inter-Laboratory Study on Measuring the Surface Charge of Electrically Polarized Hydroxyapatite.

Surface charges on implants improve integration into bone and so require a clear protocol for achieving a surface charge and comparable results from different laboratories. This study sintered hydroxyapatite (HAp) at one laboratory to remove the influence of the microstructure on surface charge and then polarized/depolarized the pellets at two different laboratories (in Tokyo and Riga). Surface charges on HAp pellets induced by electric polarization at 400 °C in a 5 kV/cm DC electric field were measured by the thermally stimulated depolarization current (TSDC) method as 6-9 µC/cm2. The surface charge results were comparable between laboratories and also agreed with previously documented values. Recommendations describe conditions for polarization and depolarization to generate a surface charge and repeatedly achieve a comparable outcome. A visual display of the polarization mechanisms and the contribution to surface charge point to further aspects that need further development.

Depressing relaxation and conduction loss of polar polymer materials by inserting bulky charge traps for superior energy storage performance in high-pulse energy storage capacitor applications.

Polymer-based dielectrics are chiefly used in high-pulse energy storage capacitors for their high breakdown strength, prominent processability, and low cost. Nevertheless, state-of-the-art commercial polymer-based dielectrics such as biaxially oriented polypropylene (BOPP), cannot satisfy the high energy density requirement in many fields because of their low permittivity. Limited success has been achieved in developing polar polymeric dielectrics with high energy density because of the quickly increased energy loss from polarization relaxation and charge conduction under a high electric field and temperature. To achieve high energy density and low loss in polar polymer dielectrics simultaneously, electron-deficient vinyl quinoline (VQQ) units are pre-copolymerized with methyl methacrylate (MMA) followed by blending with a PMMA matrix. The bulky and electron-deficient VQQs have successfully depressed the relaxation of PMMA and significantly decreased charge conduction under an elevated electric field. As a result, a rather high energy discharging efficiency (over 90%) could be finely maintained up to 800 MV m-1, and an energy density of 16.1 J cm-3 could be obtained, which are much better than those of reported polymer dielectrics. The strong space charge trapping effect of the low content of VQQ is well addressed by thermally stimulated depolarization currents (TSDC) and density functional theory analysis (DFT) of increasing breakdown strength, energy density and discharging efficiency. This work offers a promising strategy for achieving high energy density and low loss in polar polymer dielectrics for their commercial application in energy storage capacitors.