Large Dielectric Constant Research Articles

Enhanced dielectric performance of BaxSr(1-x)TiO3 films prepared by the direct current micro-arc oxidation in the presence of ethylenediamine tetraacetic acid

BaxSr(1-x)TiO3 (BST) thin-films are fabricated on a Ti-substrate by micro-arc oxidation method in the presence of an aqueous solution of ethylenediamine tetraacetic acid (EDTA) and effects of EDTA, as additive, are investigated on the micro-structure and dielectric properties of BST thin-films. The obtained results show that EDTA delays the micro-arc oxidation reaction and results in a controllable slow-growth of the thin-film. Although, a remarkable thin film is obtained, however, capacitance of the prepared film is prominently increased. When concentration of EDTA is 0.05 M, the best compactness and smoothness for the film are observed. Moreover, the largest dielectric constant and smallest dielectric-loss are attained. In addition, the largest residual polarization strength (2Pr) of 3.4 μC/cm2 is also attained under this condition.

Structural and dielectric properties of B2O3/Li2O-added Ba0.6Sr0.4TiO3 multilayer ceramics for tunable devices

B2O3 and Li2O (B/L)-added Ba0.6Sr0.4TiO3 (BST) ceramics sintered at 940 °C exhibited a dense microstructure with large grains. The amount of B/L additive was 4.5 wt% with a B/L ratio of 1.5:1. The B/L-related liquid phase assisted the densification of the BST ceramics. This BST ceramic displayed a large dielectric constant (εr) of 2834 with a low dielectric loss (tan δ) of 0.21% at 1.0 MHz. It also displayed a large tunability (28.2% at 10 kV/cm) and a high figure of merit (FOM) of 134. BST thick-films were synthesized using the tape casting method. The thick-film densified at 940 °C exhibited a large tunability of 18.7% at 10.0 kV/cm and an FOM of 208; these are higher than the values reported in the literature. Multilayer ceramics (MLCs) consisting of five layers of 40-μm-thick BST thick-films and Ag electrodes were also fabricated at 940 °C. No diffusion occurred between the Ag electrode and BST thick-film. A large tunability of 67.6% at 52 kV/cm with a high FOM of 294 was obtained from this MLC. This verified that the B/L-added BST ceramic is effective for application in tunable multilayer devices.

Physical properties in nano-crystalline Ho2CoMnO6

3d based double perovskite materials have received much attention in recent years due to their exotic magnetic structure and magneto-electric coupling. In this work we have prepared and studied the nano-crystalline sample of Ho2CoMnO6. Structural, magnetic, Raman and dielectric properties have been studied in detail. The structural analysis shows that the sample crystallize in monoclanic crystal structure with P21/n phase group. The X-ray photoelectron spectroscopy have been employed to confirms the charge state of cations presents in the material. Magnetic study shows that the sample undergoes a paramagnetic to ferromagnetic phase transition around Tc ~85 K. The isothermal magnetization measurements shows hysteresis curve hence confirm ferromagnetic behavior at low temperature. Temperature dependent Raman study reveals that there is spin phonon coupling in the sample marked by deviation in phonon mode from anharmonic behavior. Dielectric response of Ho2CoMnO6 shows the large dispersion and large dielectric constant. Impedance spectroscopy and electrical modulus study reveal that system shows deviation from ideal Debye model. AC conductivity have been studied as a function of both temperature and frequency. We found that the conduction mechanism is obeyed by Jonscher's model. The exponent factor n is suggest that the material deviates from ideal Debye model.

Dielectric properties of epoxy resin impregnated paper insulation in different stages of partial discharge development

AbstractTo investigate the variation of dielectric properties of epoxy resin impregnated paper insulation in different stages of partial discharge (PD) development, a PD experimental platform was established and epoxy resin impregnated paper insulation samples were prepared. According to the discharge amount, the number of discharges and discharge phenomena during the PD process, the PD process is divided into an initial stage, development stage, burst stage, and near‐breakdown stage. The variations of dielectric constant and dielectric loss factor of the sample during different PD development stages were measured by frequency domain dielectric spectrum tester. Scanning electron microscopy was used to observe the microscopic morphological changes of the samples at different stages of PD development. The surface characteristic functional groups at different stages of PD development of the sample were determined by Fourier transform infrared spectroscopy. The results show that: as the PD progresses, the insulation performance deteriorates; under continuous bombardment by high‐speed electrons, the network structure of the fiber surface and the epoxy molecular chain are destroyed, causing the weakening of the binding force between the molecular chains, and the short‐chain structure formed by cracking has a stronger steering ability. Under the continuous action of PD, the inside of the long‐chain molecule breaks and oxidizes, and a large number of small molecules, such as free radicals and monoglucose, are formed. The decrease in the molecular weight of the polymer leads to the weakening of the interaction between the molecules, resulting in an increase in polarization, a large dielectric constant, and an increase in the dielectric loss factor.

Bicomponent poly(ethylene)/poly(propylene) fiber bonding using dielectric inks

A dielectric ink thermal processing method has been developed to bond bicomponent poly(ethylene)/poly(propylene) (bico-PE/PP) fibers that are commonly used to make nonwoven fabrics for a variety of applications including medical, hygiene, and filtration needs. Dielectric inks applied to the fibers offer a number of potential advantages over conventional calendar bonding including more efficient energy conversion, faster heating rates, heating directed to desired bond sites, facile patterning, the ability to function on materials with substantial amounts of loft, and avoidance of fiber damage induced by calendar roller contact. Poly(ethylene) and poly(propylene) do not efficiently convert microwave energy to heat on their own; therefore, propylene carbonate (PC) and glycerine carbonate (GC) were selected as ink candidates due to their large dipole moments and dielectric constants. The temperature-dependent dielectric constant and dielectric loss values of both carbonates were measured as well as their thermal responses to microwave energy at 2.45 GHz. The dispersion of each carbonate on bico-PE/PP fibers, including the application to nonwoven fabrics, was characterized by optical microscopy. The thermal response for ink loading as a function of microwave radiation exposure time was investigated. Tensile test results showed that the bonding strength of dielectric ink bonded samples was comparable with the bonding obtained using conventional calendar bonding. The results presented herein demonstrate that dielectric inks provide fast heating rates, excellent fiber bonding, and the ability for facile nonwoven patterning.

Structural, Electrical and Dielectric Properties of Dodecylbenzene Sulphonic Acid Doped Polypyrrole/Nano-Y2O3 Composites

We report a facile strategy to synthesized the PPy-DBSA-Y2O3 composites with increasing amount of Y2O3 (2%, 4% and 8%) by in situ polymerization method. The samples were characterized by XRD, FTIR, SEM and dielectric spectroscopy. Structural and morphological analysis reveals the conformation of composite formation, increase in crystallinity and particle size also increased by doping Y2O3 into PPy-DBSA matrix. The frequency dependent AC conductivity (σac), dielectric constant (ε′) and loss factor (ε″) were measured in the frequency range from 20 Hz to 1 MHz. All measured quantities; σac, ε′ and ε″ are enhanced with increase in Y2O3 content in the composites at all frequencies. Dielectric constant value for all samples is very high at low frequency however decreases with increase in frequency. Synthesis of PPy-DBSA-Y2O3 composite materials with a large dielectric constant is very important for the improvement of electronic devices applications.

Orientation and electrode configuration dependence on ferroelectric, dielectric properties of BaTiO3 thin films

BaTiO3 (BTO) thin films with an SrRuO3 buffer layer have been deposited on a range of lattice mismatched substrates, including single crystalline (111)-oriented LaAlO3 and (100)-, (110)-, and (111)- oriented SrTiO3 substrates by pulse laser deposition. The results show that the crystal structure of BTO film is affected by the type and orientation of the substrates. The BTO films exhibits strong ferroelectric and dielectric anisotropy. Different electrode configurations affect the voltage required for polarization, but do not affect the final polarization state. The (111)-oriented film exhibits a large polarization Ps=92.43μC/cm2, Pr=51.74μC/cm2, the (100) orientation has a smaller coercive field EC=19.52 kV/cm and a leakage current, and the (110) orientation has a larger dielectric constant.

Experimental and numerical simulation analyses of selective fragmentation of coal samples by plasma

To reveal the principles of fracture extension within coal under the impact of plasma, the fracture and mineral phase of Hongliu bituminous coal were experimentally extracted through 3D visual software Dragonfly. Besides, the principles of fracture extension within coal in different directions were further analyzed under the impact of plasma. The results show that fractures on axial and horizontal surfaces both extend along minerals, which indicates that the distortion of electrical field on the boundaries between minerals and coal leads to the concentration of stress. The distribution of minerals serves to lead fracture extension, and plasma forms a spatial network fracture structure within the coal. The results indicate that electrical field intensity can be distorted among dielectrics with various dielectric constants. The intensity of electric filed is low when passing through the dielectric with a large dielectric constant, whereas it is high when passing through the dielectric with a small dielectric constant. Furthermore, aiming at investigating selective fragmentation of coal sample by plasma path, an experiment was performed by drilling boreholes and infusing iron powder in coal samples before electric breakdown. The results show that fractures extend along the drilling boreholes and run through some drilling boreholes, suggesting that the iron powder that has infused in the boreholes disturbs the plasma path. Besides, plasma paths are also influenced by the location and amount of drilling boreholes, as well as their distances to the electrode center. The results of experiment and numerical simulation are mutually validated.

Ternary nitride semiconductors in the rocksalt crystal structure

Inorganic nitrides with wurtzite crystal structures are well-known semiconductors used in optical and electronic devices. In contrast, rocksalt-structured nitrides are known for their superconducting and refractory properties. Breaking this dichotomy, here we report ternary nitride semiconductors with rocksalt crystal structures, remarkable electronic properties, and the general chemical formula Mgx TM 1-xN (TM = Ti, Zr, Hf, Nb). Our experiments show that these materials form over a broad metal composition range, and that Mg-rich compositions are nondegenerate semiconductors with visible-range optical absorption onsets (1.8 to 2.1 eV) and up to 100 cm2 V-1⋅s-1 electron mobility for MgZrN2 grown on MgO substrates. Complementary ab initio calculations reveal that these materials have disorder-tunable optical absorption, large dielectric constants, and electronic bandgaps that are relatively insensitive to disorder. These ternary Mgx TM 1-xN semiconductors are also structurally compatible both with binary TMN superconductors and main-group nitride semiconductors along certain crystallographic orientations. Overall, these results highlight Mgx TM 1-xN as a class of materials combining the semiconducting properties of main-group wurtzite nitrides and rocksalt structure of superconducting transition-metal nitrides.

Investigation of giant dielectric and room temperature ferromagnetic response of facile CZTO nanostructure

Cubic CoZnTiO4 (CZTO) nanocomposite structure has been synthesized via a modest chemical method at a much lower calcination temperature. The possible phase formations and crystalline nature of the as synthesized structure has been studied by X-ray diffraction technique. FESEM micrographs depict the grain growth within the nanocomposite. Thermal analysis shows endothermic as well as exothermic peaks which points out the thermal stability over the observed temperature range. The synthesized CZTO nanocomposite structure shows nearly frequency independent giant dielectric response on application of external electric field. The nanostructure shows e′ ~ 21,000 at 40 Hz frequency. With the help of internal barrier layer capacitor model, the origin of this large dielectric constant is well explained. The impedance spectroscopy analysis and equivalent circuit response also supports the obtained result. On application of external magnetic field, the synthesized CZTO sample also shows room temperature ferromagnetic response. This magneto-dielectric response of CZTO nanostructure enables it to be a superior material for forthcoming device application.

Dielectric and magnetocaloric study of TmCrO3

Dielectric and magnetocaloric measurements are carried out for the chromite TmCrO3. This oxide was reported to be multiferroic below the Néel temperature (TN) of ∼125 K, likely due to a structural transformation. The dielectric response shows large dielectric constants below 300 K. However, from the analyses of loss tangent, AC conductivity and dielectric modulus, this behavior is rooted in hopping of charge carriers rather than electric dipoles, as proposed for some other chromites. No dielectric anomaly is found at TN. The magnetocaloric effect shows that the magnetic transitions at TN as well as the spin reorientation temperature are of a second order. This result strongly suggests the absence of magnetostructural transition at TN in accord with no observation of ferroelectric transition at this temperature.

Effect of Ca doping on the properties of Sr2Bi4Ti5O18 ferroelectric thin films

This study examined the effect of Ca doping on the properties of Sr2Bi4Ti5O18 (SBTi) ferroelectric thin films. According to the results of the study, the performance of SBTi thin films are improved by suitable Ca doping. It can be seen from XRD analysis, all of the thin films formed a bismuth layered perovskite structure without other impure phases. SEM shows that the sample with a doping content of 10 mol% has good crystallization, uniform grain size and good film density. Compared with the characteristics of other films, the thin film sample with 10 mol% Ca shows high crystallinity, the lowest Ti3+ content, the lowest oxygen vacancy concentration, and with the large remanent polarization 2Pr = 33.5 μC/cm2, the double coercive field 2Ec = 182.8 kV/cm; furthermore, the leakage current density is 1.67 × 10−7 A/cm2. The film sample doped with 10 mol% Ca also displays better dielectric properties, with a larger dielectric constant (er = 795) and lower dielectric loss (tanδ = 0.03) when the test frequency is 105 Hz. The dielectric tunability T = 18.6% at 200 kV/cm and 500 kHz.

Enhanced dielectric properties of barium strontium titanate thin films by doping modification

Barium strontium titanate (BaxSr1–xTiO3, BST) thin films have large dielectric constant, low dielectric loss, especially the high dielectric tunability, which make them prospective candidates for microwave tunable applications. Resent developments in BST thin films by doping modification are reviewed. The A-site doping, B-site doping, and both sites codoping modifications are summarized and analyzed, respectively. The comparison of dielectric properties and microstructure of the BST thin films with different sites doping modifications is critically analyzed. The single A-site or B-site doping modification cannot obtain the BST thin films with balanced enhancement of the dielectric properties. However, the different elements codoping in both A-site and B-site of BST thin films is demonstrated to be an effective method to achieve balanced dielectric property optimization.

Enhanced energy storage density in Sc3+ substituted Pb(Zr0.53Ti0.47)O3 nanoscale films by pulse laser deposition technique

Highly oriented Pb(Zr0.53Ti0.47)0.90Sc0.10O3 (PZTS) thin films were deposited on La0.67Sr0.33MnO3 (LSMO) buffer layer coated on MgO (100) substrates by following two subsequent laser ablation processes in oxygen atmosphere employing pulse laser deposition technique. The PZTS films were found to grow in tetragonal phase with orientation along (100) plane as inferred from x-ray diffractometry analysis. The structural sensitive symmetric E (LO2) Raman band softened at elevated temperature along with its intensity continuously decreased until it disappeared in the cubic phase above 350 K. The existence of broad Raman bands at high temperature (>350 K) is attributed to the symmetry forbidden Raman scattering in relaxor cubic phase due to symmetry breaking in nano length scale. The temperature dependent dielectric measurements were performed on metal-ferroelectric-metal capacitors in the frequencies range of 102–106 Hz was observed to be diffused over a wide range of temperature 300–650 K and exhibits high dielectric constant ~5700 at room temperature. An excellent high energy storage density (Ure) ~54 J/cm3 with efficiency ~70% was estimated at applied voltage 1.82 MV/cm. High DC breakdown strength, larger dielectric constant and high restored energy density values of our PZTS thin films indicate its usage in high energy storage applications.

Microstructure, dielectric and enhanced multiferroic properties of Fe3O4/PbZr0.52Ti0.48O3 composite ceramics

Magnetoelectric composite ceramics Fe3O4/PbZr0.52Ti0.48O3 with different molar ratios (Fe3O4/PbZr0.52Ti0.48O3 = 1:1, 1:2 and 1:8) were prepared by combining hydrothermal method and sol–gel method, effects of molar ratio on the structure, dielectric and multiferroic properties were investigated. The results indicate that the synthesized composites show bi-phase structure, ruling out the presence of any obvious impurity phases. The grains can be divided into two types, the larger grain is attributed to PbZr0.52Ti0.48O3 while the smaller one can be considered to be Fe3O4. With the molar ratio increasing, the grain shape of PbZr0.52Ti0.48O3 changes from stripe to bulk-like while the shape and size of Fe3O4 is near the same. Both the dielectric constant and loss decrease with frequency, the specimen with the molar ratio of 1:8 shows the largest dielectric constant, while the sample has the lowest dielectric loss when the molar ratio is 1:2. With the increase of molar ratio, the height of the relaxation peak decreases and the peak position shifts to higher temperature. When the molar ratio is 1:8, the relaxation peak disappears due to less interface polarization. The remnant polarization increases with increasing the molar ratio, the maximum value is 1.12 μC/cm2, obtained at 1 kHz when the molar ratio is 1:8. Anomalous magnetic properties are observed, in which the magnetization increases first and then decreases with molar ratio, the largest saturation magnetization is ~ 30 emu/g when the ratio is 1:2 due to the strong interface interaction. The sample with the ratio of 1:1 shows the largest magnetic loss because of the highest content of magnetic phase. The magnetization shows a monotonic variation behavior with the molar ratio, indicating the strong interface interaction between the two phases. The maximal ME coupling coefficient is about 5.12 mV/(cm.Oe) for the sample 1:2 due to the stronger magnetic and ferroelectric properties.

Thickness dependent dielectric properties of calcium copper titanate ceramics measured in a controlled atmosphere

Abstract Phase pure CaCu3Ti4O12 CCTO ceramics are prepared by solid-state synthesis route. The effect of measuring atmospheres (air and dry N2) on the stability and reproducibility of electrical properties of CCTO as a function of sample thickness (as-prepared to thinned down) is investigated. As-sintered CCTO prepared at 1080 °C for 5 h with an initial thickness of 2.31–2.32 mm is reduced subsequently by fine grinding to 1.835 mm and then to 1.65–1.5 mm. Large inconsistency in the impedance spectra is observed when the samples are measured in air despite the thickness variations. Stable and reproducible dielectric properties are obtained in dry N2. A relatively closer resistivity (∼2 × 108 Ωcm at 23 °C in N2) regardless of the sample thickness suggests the absence of any barrier layer at the sample surface. Increased space charge accumulation at grain boundaries (GBs) leading to much larger dielectric constant (e′) was observed in air at 23 °C. A temperature (from 23 °C to 225 °C) and frequency (from 1 Hz to 1 MHz) independent and stable e′ is observed when samples are tested in N2. Much lower tan δ values with large e′ are observed for both as prepared (0.010 ± 0.001 with e′ of 9,663 ± 4 at 1.4 kHz) and the thinned down (0.015 ± 0.000 with e′ of 9,352 ± 5 and 4.5 kHz) samples at 23 °C in N2.

Reflection image enhancement for photonic crystal devices by using dielectrics

We investigated the optical properties of photonic crystal devices (PCDs) using dielectrics. Different dielectrics were injected into a cell gap of the PCDs as a swelling solvent. It is evident that the PCDs reflected a deep blue color when two different materials, chiral ionic liquid (CIL) and photosensitive small molecules, were introduced. To compare the reflection images according to the different dielectrics, a well-known ionic liquid (IL) was used as a control sample. A thinner polymer layer induced a shorter wavelength, which created a strong blue shift phenomenon with a larger refraction index and a larger dielectric constant. In this paper, we obtained 12 nm of reflection enhancement with an applied voltage of 2V using an IL and a deep-blue color image by using the effects of the molecular structure of the CIL and photosensitive materials.

Effects of post-metallisation annealing on surface–interfacial and electrical properties of HfO2/Ge stacks modified in situ with SiO2 interfacial layer

The effects of post-metallisation annealing (PMA) at 400 °C for 30 min in an NH3 ambient on the interfacial and electrical properties of a structure consisting of a Ge substrate coated with HfO2 by atomic layer deposition with a 3-nm-thick SiO2 interfacial layer formed in situ by a sputtering technique were evaluated. X-ray diffraction and x-ray photoelectron spectroscopy analyses confirmed the crystallinity of HfO2 and chemical bonding of the HfO2/SiO2/Ge interface before and after the annealing. Clear stretch-free distinct capacitance–voltage curves were observed for the sample after the PMA. According to the electrical measurements, the sample after the PMA exhibited a large dielectric constant (k ̃ 17), low interface trap density (Dit = 1.8 × 1012 cm2 eV−1), and small oxide charge (Qeff = 2.54 × 1012 cm2 eV−1). The gate leakage current of the PMA device determined using the current–voltage curve was approximately 0.1 × 10−4 A cm−2 at Vg+ = +1 V. These results suggest that the SiO2 interfacial layer formed in situ and NH3−PMA significantly improved the structural, interfacial, and electrical characteristics of the HfO2/Ge stacks for future Ge-based complementary metal–oxide–semiconductor device applications.

Novel nitrile-butadiene rubber composites with enhanced thermal conductivity and high dielectric constant

Nitrile-butadiene rubber (NBR) composites filled with functionalized BN platelets were successfully prepared to yield materials with high thermal conductivities and dielectric constants. To enhance the interfacial interactions between BN platelets and NBR matrix, non-covalent functionalization of poly(dopamine) (PDA) followed by covalent functionalization of γ-(2,3-epoxypropoxy)propytrimethoxysilane (KH560) were employed for BN platelets surface modification to yield BN-PDA-KH560. This route led to good filler dispersion of BN-PDA-KH560 plateltes with decreased interfacial thermal resistances. Large thermal conductivity (0.409 W/mK) was achieved with 30 vol% BN-PDA-KH560/NBR composite. This value was 2.6 folds higher than that of pure NBR (0.157 W/mK). The 30 vol% BN-PDA-KH560/NBR composite not only exhibited relatively high dielectric constant (9 at 100 Hz) but also remained low dielectric loss tangent (0.12 at 100 Hz). Overall, these findings provide a simple and effective route for preparing high-performance NBR composites with large thermal conductivities and dielectric constants for potential application in electronic devices.

(Invited) Bi-Based Solar Absorbers for Thin-Film Photovoltaic and Solar Fuels

Extensive deployment of solar energy conversion systems requires the development of materials and technologies which go beyond utility-scale Si photovoltaics (PV) solar cells. For instance, thin-film technologies (currently dominated by CIGS and CdTe) are particularly suited to flexible and building integrated PV, a sector predicted to grow to global market revenues of over $5bn by 2025.1 In the lower TRL scale, monolithic integrated III-V tandem devices have pushed the efficiency of photo-electrochemical (PEC) water-splitting to levels which can compete with PV powered electrolysers.2-4 However, PEC systems are yet to show the levels of stability, performance and balance of costs required for technological deployment. As elegantly exposed by Rajeshwar and colleagues,5-6 both fields require exploring the vast space provided by solid-state chemistry in order to identify new families of compound semiconductors with: (i) appropriate band gap for solar energy conversion, (ii) optimal electronic properties featuring high carrier mobility and defect tolerance, (iii) processable by solution-based methods and (iv) composed of Earth abundant and low-cost materials. Defect tolerance is a key descriptor in the search of new solar absorbers, in which Bi3+ and Pb2+ are key cations exhibiting large spin-orbit coupling, dielectric constants and band dispersion.7,8 In a recent study, we have shown that high quality polycrystalline PbI2 thin films exhibit ideal photoelectrode properties towards hydrogen evolution, following the Gartner-limit down to the flat-band potential.9 In this contribution, we will present our recent studies on Bi based absorbers including BiFeO3 and BiI3. BiI3 is prepared by spontaneous gas-phase iodination of Bi2S3 films at 200˚C.10 The films exhibit a high degree of phase purity, p-type conductivity (acceptor density of the order of 1015 cm-3) and a band gap of 1.7 eV. Thin-film devices with the structure Glass/FTO/TiO2/BiI3/F8/Au, where F8 is Poly(9,9-di-n-octylfluorenyl-2,7-diyl), display open-circuit voltage above 600 mV and record power conversion efficiency of 1.2% under AM 1.5G illumination. We have implemented a similar approach to the preparation of high quality BiFeO3 thin films, in which thermolysis of the sulphide precursor is carried out in air. Our early work on devices with the structure graphite/BiFeO3/ZnO/ITO/SLG yielded conversion efficiencies close to 4%, which is among the highest for all-oxide PV systems.11 We shall also contrast the PEC hydrogen generation of BiFeO3 with other poorly understood materials such as BiOCl.12