Depolarization Current Technique Research Articles

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.

Relaxation behaviour of pristine and ZnO impregnated PS nanocomposite films using thermally stimulated depolarization current technique

Thermally stimulated depolarization current studies of pristine and ZnO doped nanocomposite films (at 5, 10, 15 & 20 wt% of ZnO) have been investigated at different poling temperatures and polarizing fields. Peaks corresponding to glass transition temperature (α1 and α2-peaks) relaxation, space-charge relaxation (ρ-peaks) and γ-relaxation were observed in thermograms of pristine and doped films. The change in peak height and peak positions with increase in doping concentration and poling parameters i.e., EP & TP results to the trapping or detrapping of the charge carriers. The anomalous behaviour of PS/ZnO nanocomposite films towards TSD current spectra observed near the glass transition temperature indicates the phase transitions. Changes in different relaxations may be attributed to the structural deformation of the samples due to doping and supported by FTIR and SEM results. Moreover, some molecular parameters like activation energy (Ea) and relaxation times (τ) were estimated.

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.

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

Ion migration study in acid‐leached soda–lime–silica glass by thermally stimulated depolarization current analysis

AbstractIonic conductivity in silicate glasses is a major issue in the energy sector due to its detrimental effect on electric energy generation and storage and has received increasing attention over the past years. In this study, surface modification of soda–lime–silica (SLS) float glass via acid‐leaching treatment (pH 1) was implemented to understand the impact on ionic transport. The acid‐leaching treatment created a sodium‐depleted “silica‐like” structure in the near‐surface region with depths of 110 ± 20 nm for the air‐side and 93 ± 2 nm for the tin‐side of the SLS glass. Using the thermally stimulated depolarization current technique, two thermally activated relaxation peaks were found to be associated with different ion migration mechanisms. The first peak (P1) with activation energy of ∼0.85 eV was attributed to dc conduction of Na+ ions through the glass bulk. A second overlapping peak (P2) at a higher temperature was found to be related to a more limited Na+ ion migration through the acid‐leached structure, due to H+ conduction, or a coupled contribution of both mechanisms.

Comparison of pulsed electroacoustic and thermally stimulated depolarization current measurements of thermally poled PET electrets

We have compared measurements of a set of polyethylene terephthalate (PET) electret samples by means of pulsed electroacoustic method (PEA) and thermally stimulated depolarization current (TSDC) techniques. Samples where the α or the ρ relaxation is activated show uniform polarization and image charge at the electrodes. Different electrode configurations have been tested when external charge carriers are injected into the sample. In these experiments, differences in TSDC spectra are explained by the different blocking behavior of the electrodes. All in all, PEA in combination with TSDC turns out to be a useful technique in the study of thermally poled electrets.

Structure, defects, and microwave dielectric properties of Al-doped and Al/Nd co-doped Ba4Nd9.33Ti18O54 ceramics

Low-loss tungsten-bronze microwave dielectric ceramics are dielectric materials with potential application value for miniaturized dielectric filters and antennas in the fifth-generation (5G) communication technology. In this work, a novel Al/Nd co-doping method of Ba4Nd9.33Ti18O54 (BNT) ceramics with a chemical formula of Ba4Nd9.33+z/3Ti18−zAlzO54 (BNT-AN, 0 ⩽ z ⩽ 2) was proposed to improve the dielectric properties through structural and defect modulation. Together with Al-doped ceramics (Ba4Nd9.33Ti18−zAl4z/3O54, BNT-A, 0 ⩽ z ⩽ 2) for comparison, the ceramics were prepared by a solid state method. It is found that Al/Nd co-doping method has a significant effect on improving the dielectric properties compared with Al doping. As the doping amount z increased, the relative dielectric constant (εr) and the temperature coefficient of resonant frequency (τf) of the ceramics decreased, and the Q×f values of the ceramics obviously increased when z ⩽ 1.5. Excellent microwave dielectric properties of εr = 72.2, Q×f = 16,480 GHz, and τf = +14.3 ppm/°C were achieved in BNT-AN ceramics with z = 1.25. Raman spectroscopy and thermally stimulated depolarization current (TSDC) technique were firstly combined to analyze the structures and defects in microwave dielectric ceramics. It is shown that the improvement on Q×f values was originated from the decrease in the strength of the A-site cation vibration and the concentration of oxygen vacancies ({rm{V}}_{rm{O}}^{ cdot cdot }), demonstrating the effect and mechanism underlying for structural and defect modulation on the performance improvement of microwave dielectric ceramics.

Optical Properties, Antibacterial Activity, and Relaxation Behavior Investigation of Chitosan/Green Synthesized Silver Nanoparticles by Thermally Stimulated Depolarization Current Technique

Optical Properties, Antibacterial Activity, and Relaxation Behavior Investigation of Chitosan/Green Synthesized Silver Nanoparticles by Thermally Stimulated Depolarization Current Technique

Solid solutions of the (1-x)Ba(Ti0.50Sn0.50)O3∙xPbTiO3 system: Preparation, structural and dielectric characterization

Ceramic samples of the (1-x)BaTi0.5Sn0.5O3∙xPbTiO3 system with 0 ≤ x ≤ 1 were synthesized by solid-state reaction method. The samples were characterized by X-ray diffraction, dielectric measurements, and thermally stimulated depolarization currents (TSDCs) technique. It was established that the solid solutions with the perovskite structure were formed in the entire range of the compositions. The structure symmetry of the solid solutions changes from cubic (x ≤ 0.30) to tetragonal (x > 0.47) with increasing PbTiO3 content. The samples with 0.30 < x ≤ 0.47 contained mixtures of the tetragonal and cubic phases. The solid solutions exhibit a pronounced aging effect. This effect manifests itself as non-reproducible maxima in the temperature-dependent spectra of the dielectric permittivity ε(T,f) and losses tangent tanδ(T,f) measured around room temperature. The increase of the amount of PbTiO3 in the ceramic samples causes sequential changes of their dielectric response from that typical for relaxor ferroelectric for x = 0 – 0.3 to ferroelectric-like with a diffuse phase transition for x = 0.4 - ~0.8 and, finally, to usual ferroelectric response for x = ~0.8 – 1. The compositions with 0.20 < x < 0.40 show coexistence of both ferroelectric and relaxor properties. The temperature dependences of the TSDCs show pronounced maxima at temperatures T ≈ TC, T ∼ 100 K and T ∼ 300 K; the phenomena that are at the origin of the effects are discussed.

Hyaluronic acid — gelatin hydrogels as bioelectrets: Charge transport and dielectric polarization effects

In this work, we study the role of water molecules on the polarization processes activated on hyaluronic acid (HA), and gelatin (Gel) hydrogels at rather low hydration levels, by employing mainly broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC) technique. Our results suggest that the polarization capability of the hydrogels depends strongly on the water fraction, already at temperatures as low as −90 °C, and that charge (protons) long-range mobility is inevitably related with polarization processes in the biomaterials. The polarizabilty enhances strongly at temperatures above the onset temperature for structural rearrangements and conformational fluctuations in the hydrogels. At temperatures below this critical temperature, the polarizability is related to water secondary relaxation process (ν-process) and to polarization process within ice-like structures of hydration water. These findings imply that polarization effects in biomaterials are strongly affected by contributions due to hydration water (even for traces of water).

ANN based temperature compensation for variations in polarization and depolarization current measurements in transformer

Nowadays, more than a quarter of the faults that occur in oil-filled transformers are due to the aging and deterioration of their oil-paper insulation. Therefore, condition assessment of the oil-paper insulation of oil-filled transformers, which are installed in the power grids, is very important. One of the non-destructive methods, which are currently used to distinguish the insulation condition, is polarization and depolarization current (PDC) technique. Factors such as oil conductivity, paper conductivity, moisture content, temperature and insulation aging alter PDC test results. This paper proposes a method based on artificial neural network (ANN) integrated genetic algorithm to modify the effect of temperature variation in the results of PDC tests. For this purpose, PDC tests are performed on two different transformers at temperatures of 22 °C, 30 °C, 40 °C, 50 °C, 60 °C and 70 °C with the help of Megger-IDAX 300 device, which is capable of performing PDC tests up to 70 °C. To achieve the desired temperatures, the transformers are placed in the thermal furnace and with special thermal cables; the terminals of the devices are connected to the transformers inside the furnace. According to the results of depolarization current, which are measured at different temperatures, the parameters of the insulation model have been estimated by using genetic algorithm (GA). The insulation model parameters corresponding to 22 °C temperature in each transformer are selected as target parameters. Insulation model parameters related to higher temperatures are applied as inputs to the artificial neural network (ANN). This is done in order to train the ANN. The purpose of artificial neural network training is to transmit parameters related to higher temperatures on target parameters. Finally, with the help of the transferred model parameters, the polarization and depolarization current curves are drawn and transferred on the target curves (curves of 22 °C). The transfer error is calculated by the mean square error (MSE) index. Comparison of the proposed model results with the traditional method, which is based on the Arrhenius equation, in correcting the effect of temperature on the PDC test results, confirms the prediction accuracy of the proposed method.

A study of material stoichiometry on charging properties of SiNx films for potential application in RF MEMS capacitive switches

This work presents an in depth investigation regarding the effect of PECVD silicon nitride (SiNx) stoichiometry on its charging mechanisms. The investigation took place in SiNx dielectric films with different Si-content (x = 0.47–1.04) with the aid of Metal-Insulator-Metal capacitors. The experimental assessment involved a single-point Kelvin probe System, the monitoring of Current – Voltage characteristics and the employment of Thermally Stimulated Depolarization Currents technique. The results indicate that when Si-content increases the injected charge distribution is expected to extend deeper in the dielectric films and charges are displaced faster through the bulk material and towards the bottom electrode. The effective temperature is used in order to investigate hopping conduction that dominates charge transport in the bulk material and thus a more realistic approach of the discharging process is presented. Finally, the increase of Si-content seems to introduce defect states in SiNx, which are probably associated to Si-dangling bonds, and the presence of discrete depolarization mechanisms are investigated, the characteristics of which are analytically described taking into consideration the effect of stoichiometry. These results that can be useful in material engineering in order to improve the lifetime of RF MEMS capacitive switches.

Relaxation Behavior of Thermoplastic Polyimide R-BAPB in the Amorphous State

The molecular mobility of poly(4,4'-bis(4-aminophenoxy)biphenyl)imido-1,3-bis(3,3'-4,4'-dicarboxyphenoxy)benzene) films is studied by the thermally stimulated depolarization current (TSDC) technique and dielectric spectroscopy. The existence of two dipolar polarization relaxation regions (β and α) related to the local mobility in the glassy state and the cooperative segmental mobility in the rubbery state, respectively, is revealed. The temperature dependences of the relaxation time for the β-process obey the Arrhenius equation; for the α-process, they obey the Vogel–Tammann–Hesse equation. Emergence of the third peak βI is related to relaxation of the space homocharge. The molecular mechanisms of all the observed processes are revealed.

Electret mechanisms and kinetics of electrospun nanofiber membranes and lifetime in filtration applications in comparison with corona-charged membranes

Due to recent serious air pollution especially in Asian countries, electret air filters with ultra-high efficiency have attracted much attention. However, the crucial issue of restraining charge dissipation to maintain stable electrostatic capture efficiency is still challenging. Herein, electret mechanisms, charge degradation kinetics and lifetime in filtration applications of electrospun membranes and corona-charged membranes exposed to isopropanol vapor and high humidity were studied. The surface potential degradation was measured in an in-situ discharging and monitoring setup. Electrospun membranes have longer charge retention time compared to corona-charged membranes. A dual-level trap model based on shallow and deep traps was proposed to quantitatively describe charge aging characteristics. It revealed that besides surface charges, volume charges in traps with deep energy levels were also formed during electrospinning. Furthermore, the charge storage mechanism of electrospun membranes was investigated by thermally stimulated depolarization current technique, which demonstrated that volume charges were trapped in the membrane and dipole charges were generated during electrospinning. Direct charge mapping on individual electrospun nanofiber was also achieved by scanning Kelvin probe microscopy. With the benefit of volume charges in deep traps, the filtration efficiency of electrospun membranes only decreased by 3.67% after 40 h at 95% humidity. With abundant volume charges and reinforced charge stability, electrospun membranes consisting of polymers with inherent dielectric characteristics exhibit robust filtration performance and become a promising material for air pollution control.

Enhancement of dielectric properties and energy storage performance in 3Y‐TZP ceramics with BaTiO3 additives

AbstractWith the fast charge‐discharge speed and ultrahigh power density, electrostatic energy storage materials offer great potential in the applications for pulsed power systems. As a very important member of structural ceramics, 3Y‐TZP (3 mol% Y2O3 doped tetragonal zirconia polycrystals) has shown extraordinary mechanical properties. However, the research on their energy storage performance is still lacking. Herein, a ferroelectric phase, BaTiO3 (BT), was introduced and demonstrated to improve the dielectric properties and energy storage performance of 3Y‐TZP ceramic matrix via the conventional solid‐state reaction method. With increasing the BT content from 0 to 15 mol%, the permittivity of the composite ceramics could be effectively increased from 40.2 to 64.1 measured at 1 kHz. Simultaneously, the dielectric loss could be effectively decreased by depressing the response of charged defects, which was further interpreted by the thermally stimulated depolarization current technique. Meanwhile, the breakdown strength showed a typical increase‐then‐decrease trend with increasing BT content, and reached their maximum values when doped with 7 mol% BT. Together with the enhancement of dielectric properties, the 7 mol% BT‐doped 3Y‐TZP ceramics exhibited a maximum energy storage density of 0.42 J/cm3, which was approximately 150% larger than that of the pure 3Y‐TZP ceramics.

Dielectric and anti-reduction properties of (1-x)BaTiO3-xBi(Zn0.5Y0.5)O2.75 ceramics for BME-MLCC application

In this work, nominal composition (1-x)BaTiO3-xBi(Zn0.5Y0.5)O2.75 [abbreviated as (1-x)BT-xBZY, (x = 0.05, 0.1, 0.15, 0.2, 0.25)] ceramics were prepared by solid-state reaction method, and sintered in reducing atmosphere. Effect of introducing BZY on the structure, dielectric and insulating properties of BT was investigated. XRD results demonstrated that the unit cell volume of (1-x)BT-xBZY ceramics expanded with the addition of BZY, accompanied with the transformation from tetragonal to pseudo-cubic phase when x ≥ 0.05. Electrical properties measurement showed that the dielectric-temperature stability and insulating properties of (1-x)BT-xBZY ceramics were effectively improved by BZY addition, where the optimum performances were achieved at x = 0.15, with the dielectric constant of 1362 and dielectric loss of 1.4%, and resistivity of 5.5 × 1012 Ω cm at room temperature, meeting the standard of X8R specification for MLCC application. The feasible mechanism of improved anti-reduction properties for (1-x)BT-xBZY ceramics was investigated by employing X-ray photoelectron spectra (XPS) and thermally stimulated depolarization current (TSDC) testing techniques, where the formation of defect dipoles [2YTiˈ-VO..] and the deoxidation of Bi ion were revealed and considered to be responsible for the anti-reduction behavior.

Microwave dielectric properties and thermally stimulated depolarization of Al‐doped Ba4(Sm,Nd)9.33Ti18O54 ceramics

AbstractBa4(Sm0.15Nd0.85)9.33Ti18‐zAl3z/4O54 (BSNT‐zAl, 0.0 ≤ z ≤ 2.5) ceramics were prepared via a solid‐state reaction, and the effects of Al doping on the microwave dielectric properties and defect behavior of the title compound were studied. X‐ray diffraction (XRD) analysis and scanning electron microscopy (SEM) photographs suggested that Al ions successfully entered the lattice to form tungsten‐bronze‐like solid solutions. With a small amount of Al substitution, the relative dielectric constant (εr), and the temperature coefficient of resonant frequency (τf) values decreased, whereas the quality factor (Q × f) substantially increased by approximately 50%. The defect‐related extrinsic dielectric loss was clarified via the thermally stimulated depolarization current (TSDC) technique. With Al doping, the TSDC relaxation of across‐grain‐boundary oxygen vacancies () vanished, whereas that of defect dipoles () appeared at relatively low temperatures. Therefore, in the BSNT‐zAl ceramics, oxygen vacancies were more inclined to interconnect with to form defect dipoles. This could reduce the activity of and account for the notable improvement in the Q × f values. In particular, the excellent characteristics of εr = 67.33, Q × f = 16 530 GHz, and τf = +0.87 ppm/°C were achieved in the specimens with z = 1.5 sintered at 1350°C for 4 hours.

Temperature stability, low loss and defect relaxation of MgO-TiO2 microwave dielectric ceramics modified by Ca0.8Sr0.2TiO3

Temperature-stable and low-loss microwave dielectrics based on the MgO-TiO2 system with nominal formation Mgn+1TinO3n+1 (n = 5, MT) were prepared via the conventional solid-state reaction method. Ca0.8Sr0.2TiO3 (CST) was chosen as a τf compensator for matrix MT to form the composite ceramics (1-x)Mg6Ti5O16-xCa0.8Sr0.2TiO3 (0.10 ≤ x ≤ 0.26, MT-CST). The effects of CST additions on the phase composition, defect relaxation behavior, and microwave dielectric properties of MT were investigated. It revealed that undoped MT was basically consisted of MgTiO3 as a major phase and Mg2TiO4 as a minor phase, and such two phases coexisted well with CST additions. Interestingly, τf could be tuned close to zero (−1.28ppm/°C) for the MT-CST ceramics at x = 0.22, accompanied with a high Q×f value ~ 74,200GHz and a proper εr ~ 20.25 (9.90GHz). These materials possessed a good potential for applications in microwave components and devices. Meanwhile, significant relaxation phenomena were observed in all the MT-CST samples using dielectric spectroscopy and thermally stimulated depolarization current (TSDC) techniques. The oxygen-vacancy-related defects, shown as (TiTi′)-(VO••) dipoles and VO••, were the main types of defects in MT-CST, which was responsible for the relaxation behavior; meanwhile, the defect concentrations increased with the increase of CST content, thus resulting in the increase of dielectric loss at low and high frequencies.