Enhancement Of Dielectric Constant Research Articles

Effects of Aluminium Contents and Consolidation Techniques on Chemical Composition, Microstructure and Dielectric Properties of Strontium Titanate

It has been accepted that compositions and microstructures significantly affected dielectric properties of materials. In general, chemical compositions were influenced by additive contents, while consolidation techniques controlled microstructure of the materials to have appropriate grain sizes. This study, therefore, aimed at examining effects of aluminium contents and consolidation techniques on chemical compositions and microstructures of the strontium titanate. Experimental results revealed that at higher aluminium contents, only small quantities of TiO 2 secondary phase were present, while grain sizes generally decreased. The results also indicated that the cold isostatic pressing technique led to high sintered density. The greatest dielectric constant (281.5 at 1 MHz) obtained in this study was achieved in strontium titanate sample with 30 at% of Al addition, pressed by cold isostatic pressing. Enhancement of dielectric constant of the sample was attributed to low secondary phase, fine grain sizes and high sintered density.

Enhanced Thermal Conductivity and Dielectric Properties of Iron Oxide/Polyethylene Nanocomposites Induced by a Magnetic Field

Iron Oxide (Fe3O4) nanoparticles were deposited on the surface of low density polyethylene (LDPE) particles by solvothermal method. A magnetic field was introduced to the preparation of Fe3O4/LDPE composites, and the influences of the magnetic field on thermal conductivity and dielectric properties of composites were investigated systematically. The Fe3O4/LDPE composites treated by a vertical direction magnetic field exhibited a high thermal conductivity and a large dielectric constant at low filler loading. The enhancement of thermal conductivity and dielectric constant is attributed to the formation of the conductive chains of Fe3O4 in LDPE matrix under the action of the magnetic field, which can effectively enhance the heat flux and interfacial polarization of the Fe3O4/LDPE composites. Moreover, the relatively low dielectric loss and low conductivity achieved are attributed to the low volume fraction of fillers and excellent compatibility between Fe3O4 and LDPE. Of particular note is the dielectric properties of Fe3O4/LDPE composites induced by the magnetic field also retain good stability across a wide temperature range, and this contributes to the stability and lifespan of polymer capacitors. All the above-mentioned properties along with the simplicity and scalability of the preparation for the polymer nanocomposites make them promising for the electronics industry.

Enhancement of dielectric and electrical properties in BFN/Ni/PVDF three-phase composites

To develop dielectric materials with high dielectric constant and low dielectric loss, a novel three-phase composite was prepared by embedding the nano-sized Ba(Fe0.5Nb0.5)O3 (BFN) crystallites and Ni crystallites into poly(vinylidene fluoride) (PVDF) matrix. The structure, dielectric and electrical properties of the composites were investigated. The superiority of this method is that, when compared with the two-phase Ni/PVDF composites, three-phase composites not only show significantly increased dielectric constants but also have lower dielectric loss. Our results show that a high dielectric constant of 475 and a relatively low loss of 0.61 were achieved at 100 Hz with 25 vol.% Ni and 50 vol.% BFN, respectively. The enhancement of dielectric constant of polymer based composites can be interpreted by the mini-capacitor principle and the interfacial polarization. The relatively low dielectric loss could be attributed to the isolation effect of BFN fillers. These composites with high dielectric constant and low dielectric loss are found to be potentially useful for embedded capacitor applications.

Enhanced dielectric properties in (In, Nb) co-doped BaTiO3 ceramics

BaTi1-x(In0.5Nb0.5)xO3 (x=0, 0.01, and 0.03) ceramic samples were prepared using the conventional solid-state reaction method. The dielectric properties of these samples were investigated as a function of temperature (300K≤T≤700K) and frequency (102Hz≤f≤106Hz). Great enhancement of dielectric constant in the dual doped samples was found. Defect diploles of [NbTi5+-Ti3+] and [NbTi5+-InTi3+] were suggest to account for the enhancement of dielectric constant.

Room temperature synthesis of wurtzite phase nanostructured ZnS and accompanied enhancement in dielectric constant

We report the room temperature synthesis of ZnS in the wurtzite phase by using ethylenediamine, which acts as a template as well as a capping agent. With the addition of ethylenediamine, structural transformation in ZnS from cubic to wurtzite phase is observed. This is accompanied by an increase in the real permittivity by an order of 2, and reduction in dielectric loss by a factor of 6 as compared to a sample without ethylenediamine. Thus, suggesting that ethylenediamine capped wurtzite ZnS is more suitable for miniaturied capactive devices.

Graphene oxide reinforced poly (4-styrenesulfonic acid)/polyvinyl alcohol blend composites with enhanced dielectric properties for portable and flexible electronics

In this work, Graphene Oxide (GO) reinforced novel polymer composites comprising of poly (4-styrenesulfonic acid) (PSSA) and polyvinyl alcohol (PVA) blend matrix have been developed using colloidal processing technique. The properties and the structure of prepared composites were investigated using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), UV–vis spectroscopy (UV), Thermogravimetric analysis (TGA), Polarized optical microscopy (POM), Scanning electron microscopy (SEM) and Atomic force microscopy (AFM). The FTIR and Raman spectroscopy analysis indicate the strong interfacial interaction between GO and PSSA/PVA blend matrix. The XRD and SEM analysis confirm that GO was fully exfoliated into individual graphene sheets and dispersed homogeneously within the polymer matrix. The effective reinforcement of GO into PSSA/PVA blend matrix has resulted in the enhancement of dielectric constant. The dielectric constant has increased from 82.67 (50 Hz, 150 °C) for PSSA/PVA (50/50) blend to 297.91 (50 Hz, 150 °C) for PSSA/PVA/GO composites with 3 wt % GO loading. The dielectric loss (tan δ) has increased from 1.56 (50 KHz, 140 °C) for PSSA/PVA (50/50) blend to 2.64 (50 KHz, 140 °C) for PSSA/PVA/GO composites with 3 wt % GO loading. These findings provide a new insight to fabricate flexible, high-k dielectric composite as a promising material for energy storage applications.

Effect of filler particle size on electric energy density of epoxy-aluminum nanocomposites

The size effect of filler particles on the dielectric properties and maximum electric energy density of epoxy-aluminum composites are evaluated. Aluminum particles encapsulated with aluminum oxide layers are used as the fillers to enhance the dielectric constant of the composite and also to maintain the breakdown strength. Experiments were conducted to evaluate the dielectric constant, dissipation factor, breakdown voltage and maximum electric energy density of the composites as a function of filler loading. Dielectric property measurements demonstrated that, for composites containing 70 nm (average particle size) aluminum the dielectric constant is increased by a factor of 7 at 18 wt% filler loading as compared with that of pure epoxy matrix. Even if there is a reduction in breakdown strength, the addition of nanoparticles resulted in potential gain in electric energy density. To analyze the size effect of filler particles on the performance of the composites, samples with a different filler size of 40 nm (APS) were prepared and dielectric properties were evaluated. It is observed that the enhancement in dielectric constant is 6 times that of pure epoxy at a lower filler concentration of 14 wt% for 40 nm (APS) filler samples. The improvement in maximum energy density is 4 times at 18 wt% filler loading and 3.5 times at 14 wt% filler loading for 70 nm (APS) and 40 nm (APS) composites respectively. Material characteristics were analyzed using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Thermogravimetric (TGA) techniques.

Phase transition and tolerance factor relationship of lead-free (Bi0.5K0.5)TiO3-Bi(Mg0.5Ti0.5)O3 piezoelectric ceramics

A relation between phase transition region and the tolerance factor (t) in BKT-BMgT ceramics was established according to the reported literature for various BKT-based ceramics. In order to confirm the prediction, lead-free piezoelectric ceramics based on (1−x)(Bi0.5K0.50)TiO3-xBi(Mg0.50Ti0.50)O3 or (1−x)BKT-xBMgT (x=0.0–0.2) were synthesized by a solid-state reaction method. The compositional dependence of the crystal structure, electrical properties and strain behavior of all ceramics was examined. The crystal structure analysis indicated that the phase transition region was located over the compositional region 0.05<x<0.10 (t∼1.0170–1.0130), over which the crystal structure was seen to change from a tetragonal to a pseudo-cubic phase. The tolerance factor of these compositions were closely matched to expected values for the phase transition region in BKT-based ceramics (t∼1.0123–1.0192), as reported in the literatures. The ceramics in these transition region (0.05<x<0.10) showed a noticeable enhancement in dielectric constant (εr=1150–1510, Tm=323–347°C), ferroelectric properties (Pr=9.7–11.7μC/cm2) and piezoelectric properties (d33=205–225pC/N) properties, as compared to pure BKT ceramic. Furthermore, the BKT-0.10BMgT sample displayed a high Smax=0.22% and d*33=314pm/V which was ∼20–30% higher than that of unmodified-BKT ceramic. The obtained results suggested that a study of the tolerance factor may be employed in a search for the phase transition region with excellent piezoelectric properties in various ceramic systems.

Strain-induced phase variation and dielectric constant enhancement of epitaxial Gd2O3

One of the approaches for realizing advanced high k insulators for metal oxide semiconductor field effect transistors based devices is the use of rare earth oxides. When these oxides are deposited as epitaxial thin films, they demonstrate dielectric properties that differ greatly from those that are known for bulk oxides. Using structural and spectroscopic techniques, as well as first-principles calculations, Gd2O3 films deposited on Si (111) and Ge (111) were characterized. It was seen that the same 4 nm thick film, grown simultaneously on Ge and Si, presents an unstrained lattice on Ge while showing a metastable phase on Si. This change from the cubic lattice to the distorted metastable phase is characterized by an increase in the dielectric constant of more than 30% and a change in band gap. The case in study shows that extreme structural changes can occur in ultra-thin epitaxial rare earth oxide films and modify their dielectric properties when the underlying substrate is altered.

Enhancement of dielectric constant in a niobium doped titania system: an experimental and theoretical study

A very high dielectric constant of Nb doped titania is observed due to both the interfacial effect and formation of complex defect dipoles.

Electrical Properties of La-Doped Ba0.7Ca0.3TiO3 Lead-Free Ceramics

(Ba0.7Ca0.3)1-1.5xLaxTiO3 ceramics with x = 0 – 0.03 were prepared using a solid state sintering method. Upon La3+ increasing content, tetragonality of doped ceramics decreased. The intrinsic contribution affected piezoelectric coefficient decrement. The changes in dielectric loss, remanent polarization, coercive field, planar electromechanical coupling coefficient and mechanical quality factor seemed to be correlated with the extrinsic contribution from domain wall mobility. La3+ addition caused both grain size reduction and dielectric constant enhancement. The results here suggested that BCT electrical properties' dependence on La3+ substitution may be useful for ferroeletric devices.

Microstructure and electrical properties of (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free piezoelectric ceramics prepared by spark plasma sintering

The (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free piezoelectric ceramics was prepared by a spark plasma sintering technique, and the microstructure and electrical properties of (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 lead-free piezoelectric ceramics prepared by spark plasma sintering technique was investigated systematically. The result revealed that, compared with a conventional sintered (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics, a high relative densities of 99 % was achieved in (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics sintered at 1450 °C for 3 min, suggesting a very highly dense microstructure was developed by employing the spark plasma sintering technique. A relatively small grain size and the existence of internal stress was formed in (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics prepared by spark plasma sintering technique showed by the SEM and XRD, resulting in the degradation of piezoelectric and ferroelectric properties, while an enhancement in dielectric constant.

Composition-Microstructure-Property Relationships in BaTiO&lt;sub&gt;3&lt;/sub&gt; with Mg Addition

Rising worldwide demands for energy encourages development of high-efficiency energy storage and capacitor components. Main requirements for dielectric materials employed in fabrication of high energy density capacitors include high dielectric constant, high dielectric breakdown strength, and low dielectric loss. Owing to its high dielectric constant and low dielectric loss [1], barium titanate is among common capacitor materials. Tailoring of dielectric properties of barium titanate can be achieved through controlled chemical composition, microstructure, and crystal structure. Synthesis and processing techniques, as well as doping of barium titanate, can be key factors to control the composition and structure, which consequently contribute to enhancement of dielectric constant in the material.

Effects of Mg addition and sintering temperatures on chemical compositions, microstructures, densities and dielectric properties of strontium titanate

Increasing demands in dielectric capacitors for electronic applications require continuous improvement of dielectric materials in terms of enhanced dielectric constant and minimal dielectric loss. This study aimed at synthesizing strontium titanate powders doped with 10, 20, and 30at% of Mg, and examining relationships among additive concentrations, chemical compositions, sintering temperatures, microstructures, and dielectric properties of strontium titanate. Experimental findings indicated that increasing doping concentrations resulted in increased secondary phase content, MgO, which seemed to have consequently led to grain size reduction. However, MgO concentrations were found to be lower than 10wt%, which possibly have not significantly changed the sample׳s dielectric properties. The results also revealed that a higher sintering temperature has led to an increase in sample density as well as to an enhancement in dielectric constant. It was further observed that strontium titanate samples doped with 30at% Mg and sintered at 1330°C gave the highest dielectric constant value, which was ten times higher than the samples with 10at% Mg sintered at 1250°C, the sample with the lowest dielectric constant. All samples in the study though yielded dielectric losses of less than 3%, which are within the acceptable range for practical applications.

Significant enhancement in dielectric constant of polyimide thin films by doping zirconia nanocrystals

Polyimide thin film has a low dielectric constant of 3.2. In this paper, we fabricated polyimide/ZrO2-nanocrystals hybrid thin films with a high dielectric constant of 6.1. The polyimide/ZrO2-nanocrystals hybrid thin films were formed by a spin-coating and a sintering process. The organic/inorganic hybrid thin films were characterized by X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, and LCR meter. Our experimental results confirmed that ZrO2 nanocrystals were well dispersed and embedded in the hybrid thin films. Compared with pristine polyimide thin film, the dielectric constant of polyimide/ZrO2-nanocrystal hybrid thin film significantly increased due to the incorporation of inorganic component.

BaTiO3 based relaxor ferroelectric epitaxial thin-films for high-temperature operational capacitors

The epitaxial growth of 0.6[BaTiO3]–0.4[Bi(Mg2/3Nb1/3)O3] (BT–BMN) relaxor ferroelectric thin-films on (100) Nb doped SrTiO3 substrates has been achieved and the structure is investigated for high-temperature capacitor applications. The post growth annealing decreases the oxygen vacancy and other defects in BT–BMN films, resulting in the enhancement of dielectric constant. An insertion of intermediate SrRuO3 layers as an electrode instead of Pt, sandwiching the film, is found to be more effective in enhancing the dielectric constant. A very high dielectric constant exceeding 400 was achieved from high-temperature annealed film and the film showed an excellent dielectric constant stability of below 11% in the temperature range of 80–400 °C. This will enable smaller, high-temperature tolerant, monolithically integrated thin-film capacitors on power semiconductor devices.

High temperature Bi-based ferroelectric solid-solution with enhanced dielectric properties and magnetic order

Substitution of Fe3+ at B-site in 0.45(BiMg0.5Zr0.5O3)–0.55(PbTiO3) (BMZ–PT) solid solution [(BiMg0.5(1−x)Zr0.5(1−x)FexO3)0.45–(PbTiO3)0.55, for x=0.30, 0.35, 0.45 and 0.50] enhances the tetragonality (c/a ratio), dielectric constant (ε׳), ferroelectric curie temperature (TC) and polarization values with increasing Fe content. We show that the samples fall in the category of Bi(B′B″B′′′)O3–PbTiO3 type solid solutions possessing high TC (highest being ~434°C for x=0.50). The variations of c/a ratio and ferroelectric TC with Fe content show non-linear trends. Using impedance spectroscopy, a single relaxation process (solely due to grains) could be identified in these solid solutions. However, detailed study of ac conductivity indicates that the conduction mechanism is dependent on frequency as well as Fe content. The ac conductivity measurements also point out that the small and large polaron hopping conduction is responsible for enhancement in dielectric constant in these samples. The sample with largest Fe content also shows magnetic ordering.

The effect of nanographite addition on the physical properties of poly(vinylidene fluoride)/hydroxypropyl cellulose blend

In this study, polymeric films of poly(vinylidene fluoride) (PVDF)/hydroxypropyl cellulose (HPC) blend filled with various graphite-nanoparticles (GNP) contents were prepared via solvent-mixing technique. The compatibility between PVDF and HPC polymers was studied. The variations in structure, dielectric and thermal properties were investigated over the frequency range (20 Hz–3 MHz) and temperature range (20–110 °C). The X-ray diffraction and differential scanning calorimetry results reveal that the crystallinity of PVDF was affected by the presence of HPC and GNP. The dielectric results reveal that the great enhancement of dielectric constant ( $$\upvarepsilon^{{\prime }}$$ ) and ac conductivity (σac) were observed. The dielectric properties were explained in terms of the dielectric polarization mechanism. Both HPC and GNP additions enhance the $$\upvarepsilon^{{\prime }}$$ of PVDF due to the formation of β-phase polymorph and the interface effect between the GNP and blend matrix. The improvement of the thermal stability was observed due to the regular arrangement of the side chains. The easy processing, high dielectric constant, low tangent loss and high thermal stability of the composites make the composites attractive for practical applications in embedded capacitors.

Vertically Aligned Carbon Nanotube Arrays on SiC Microplatelets: A High Figure-of-Merit Strategy for Achieving Large Dielectric Constant and Low Loss in Polymer Composites

Inclusion of conducting nanoparticles into polymer could result in a nonpercolated nanocomposite with largely improved dielectric constant. But the challenge always relies on lowering dielectric loss near percolation by rationally designing composite microstructure. Herein, we report a general strategy for dielectric constant enhancement employing vertically aligned carbon nanotube (CNT) arrays as filler. The CNT arrays are well distributed into poly(vinylidene fluoride) matrix with the help of SiC microplatelet support. They can naturally form effective microcapacitors in series to store charges and thus afford a dielectric constant of hundreds times higher than the virgin polymer yet maintain the loss tangent at low levels (<0.43). More importantly, such improvement is achieved at a very low loading, demonstrating the highest figure of merit ever reported for a nonpercolated system. Thanks to the thermal stability of the formed microcapacitor networks, the CNT array-based composite exhibits a giant dielectric constant of ∼105 and a moderate loss tangent of ∼7 at temperatures as high as 170 °C. All these results validate the effectiveness of our strategy to realize high-performance dielectric polymer composites.

Enhancement of dielectric constant in transition metal doped ZnO nanocrystals

We have presented dielectric studies on Zn1−xCoxO, Zn1−xFexO, and Zn1−xFex/2Cox/2O (x = doping level) semiconducting nanoparticles (∼2–40 nm). For all those samples, dielectric constant (є) is found to exhibit a maximum with x. Enhancement of є is found to be ∼250 times for Zn0.85Co0.15O and ∼400 times for Zn0.8Fe0.1Co0.1O from that of ZnO. Presence of effective higher oxidation state of transition metals ions in ZnO due to Fe/Co doping resulting in space charge polarization possibly yields this effect. The simultaneous existence of high є, semiconducting, and ferromagnetic like behaviour at 300 K seems to propose Zn0.8Fe0.1Co0.1O, promising for technological application.