Influence of nanogold additives on phase formation, microstructure and dielectric properties of perovskite BaTiO3 ceramics

NASA Astrophysics Data System (ADS)

Nonkumwong, Jeeranan; Ananta, Supon; Srisombat, Laongnuan

2015-06-01

The formation of perovskite phase, microstructure and dielectric properties of nanogold-modified barium titanate (BaTiO3) ceramics was examined as a function of gold nanoparticle contents by employing a combination of X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, Archimedes principle and dielectric measurement techniques. These ceramics were fabricated from a simple mixed-oxide method. The amount of gold nanoparticles was found to be one of the key factors controlling densification, grain growth and dielectric response in BaTiO3 ceramics. It was found that under suitable amount of nanogold addition (4 mol%), highly dense perovskite BaTiO3 ceramics with homogeneous microstructures of refined grains (~0.5-3.1 μm) and excellence dielectric properties can be produced.

Dielectric Characteristics of Microstructural Changes and Property Evolution in Engineered Materials

NASA Astrophysics Data System (ADS)

Clifford, Jallisa Janet

Heterogeneous materials are increasingly used in a wide range of applications such as aerospace, civil infrastructure, fuel cells and many others. The ability to take properties from two or more materials to create a material with properties engineered to needs is always very attractive. Hence heterogeneous materials are evolving into more complex formulations in multiple disciplines. Design of microstructure at multiple scales control the global functional properties of these materials and their structures. However, local microstructural changes do not directly cause a proportional change to the global properties (such as strength and stiffness). Instead, local changes follow an evolution process including significant interactions. Therefore, in order to understand property evolution of engineered materials, microstructural changes need to be effectively captured. Characterizing these changes and representing them by material variables will enable us to further improve our material level understanding. In this work, we will demonstrate how microstructural features of heterogeneous materials can be described quantitatively using broadband dielectric spectroscopy (BbDS). The frequency dependent dielectric properties can capture the change in material microstructure and represent these changes in terms of material variables, such as complex permittivity. These changes in terms of material properties can then be linked to a number of different conditions, such as increasing damage due to impact or fatigue. Two different broadband dielectric spectroscopy scanning modes are presented: bulk measurements and continuous scanning to measure dielectric property change as a function of position across the specimen. In this study, we will focus on ceramic materials and fiber reinforced polymer matrix composites as test bed material systems. In the first part of the thesis, we will present how different micro-structural design of porous ceramic materials can be captured quantitatively using BbDS. These materials are typically used in solid oxide fuel cells (SOFC). Results show significant effect of microstructural design on material properties at multiple temperatures (up to 800 °C). In the later part of the thesis, we will focus on microstructural changes of fiber reinforced composite materials due to impact and static loading. The changes in dielectric response can then be linked to the bulk mechanical properties of the material and various damage modes. Observing trends in dielectric response enables us to further determine local mechanisms and distribution of properties throughout the damaged specimens. A 3D X-ray microscope and a digital microscope have been used to visualize these changes in material microstructure and validate experimental observations. The increase in damage observed in the material microstructure can then also be linked to the changes in dielectric response. Results show that BbDS is an extremely useful tool for identifying microstructural changes within a heterogeneous material and particularly useful in relating remaining properties. Dielectric material variables can be used directly in property degradation laws and help develop a framework for future predictive modeling methodologies.

Thermal strain-induced dielectric anisotropy in Ba0.7Sr0.3TiO3 thin films grown on silicon-based substrates

NASA Astrophysics Data System (ADS)

Zhu, X. H.; Guigues, B.; Defaÿ, E.; Dubarry, C.; Aïd, M.

2009-07-01

Dielectric properties of Ba0.7Sr0.3TiO3 (BST) thin films, which were prepared on silicon-based substrates by ion beam sputtering and postdeposition annealing method, were systematically investigated in different electrode configurations of metal-insulator-metal and coplanar interdigital capacitors. It was found that a large dielectric anisotropy exists in the films with better in-plane dielectric properties (higher dielectric permittivity and tunability) than those along the out-of-plane direction. The observed anisotropic dielectric responses are explained qualitatively in terms of a thermal strain effect that is related to dissimilar film strains along the in-plane and out-of-plane directions. Another reason for the dielectric anisotropy is due to different influences of the interfacial low-dielectric layer between the BST film and the substrate (metal electrode).

Influence of test capacitor features on piezoelectric and dielectric measurement of ferroelectric films.

PubMed

Wang, Zhihong; Lau, Gih Keong; Zhu, Weiguang; Chao, Chen

2006-01-01

This paper presents both theoretical and numerical analyses of the piezoelectric and dielectric responses of a highly idealized film-on-substrate system, namely, a polarized ferroelectric film perfectly bonded to an elastic silicon substrate. It shows that both effective dielectric and piezoelectric properties of the films change with the size and configuration of the test capacitor. There exists a critical electrode size that is smaller than the diameter of the commonly used substrate. The effective film properties converge to their respective constrained values as capacitor size increases to the critical size. If capacitor size is smaller than the critical size, the surface displacement at the top electrode deviates from the net thickness change in response to an applied voltage because the film is deformable at the film/substrate interface. The constrained properties of the films depend only on those of bulk ferroelectrics but are independent of film thickness and substrate properties. The finding of the critical capacitor size together with analytical expressions of the constrained properties makes it possible to realize consistent measurement of piezoelectric and dielectric properties of films. A surface scanning technique is recommended to measure the profile of piezoresponses of the film so that the constrained properties of the film can be identified accurately.

Dielectric Properties of Tungsten Copper Barium Ceramic as Promising Colossal-Permittivity Material

NASA Astrophysics Data System (ADS)

Wang, Juanjuan; Chao, Xiaolian; Li, Guangzhao; Feng, Lajun; Zhao, Kang; Ning, Tiantian

2017-08-01

Ba(Cu0.5W0.5)O3 (BCW) ceramic has been fabricated and its dielectric properties investigated for use in energy-storage applications, revealing a very large dielectric constant (˜104) at 1 kHz. Moreover, the colossal-permittivity BCW ceramic exhibited fine microstructure and optimal temperature stability over a wide temperature range from room temperature to 500°C. The internal barrier layer capacitor mechanism was considered to be responsible for its high dielectric properties. Based on activation values, it is concluded that doubly ionized oxygen vacancies make a substantial contribution to the conduction and relaxation behaviors at grain boundaries. This study suggests that this kind of material has potential for use in high-density energy storage applications.

Dielectric Properties of Piezoelectric Polyimides

NASA Technical Reports Server (NTRS)

Ounaies, Z.; Young, J. A.; Simpson, J. O.; Farmer, B. L.

1997-01-01

Molecular modeling and dielectric measurements are being used to identify mechanisms governing piezoelectric behavior in polyimides such as dipole orientation during poling, as well as degree of piezoelectricity achievable. Molecular modeling on polyimides containing pendant, polar nitrile (CN) groups has been completed to determine their remanent polarization. Experimental investigation of their dielectric properties evaluated as a function of temperature and frequency has substantiated numerical predictions. With this information in hand, we are then able to suggest changes in the molecular structures, which will then improve upon the piezoelectric response.

Improving dielectric properties and thermal conductivity of polymer composites with CaCu3Ti4O12 and β-SiC hybrid fillers

NASA Astrophysics Data System (ADS)

Ouyang, Xin; Cao, Peng; Zhang, Weijun; Huang, Zhaohui; Gao, Wei

2015-01-01

In this paper, we report a series of homogeneous polymeric composites with enhanced dielectric properties and thermal conductivity. The composites were constituted of polyvinylidene fluorides (PVDFs) matrix and CaCu3Ti4O12 (CCTO) monolithic or CCTO/β-SiC hybrid fillers, and prepared by simple melt blending and hot moulding technique. The influence of different types of fillers and their composition on the dielectric response and thermal conductivity of the obtained composites was studied. Results show that hybrid loading is preferred and a reasonable combination of thermal conductivity (0.80 Wṡm-1ṡK-1), dielectric constant (˜50) and dielectric loss (˜0.07) at 103 Hz was achieved in the PVDF composite containing 40 vol.% CCTO and 10 vol.% β-SiC. The strong dipolar and interfacial polarization derived from the fillers are responsible for the enhancement of the dielectric constant, while the formation of thermally conductive networks/chains by β-SiC whiskers contributes to the improved thermal conductivity.

Dielectric properties of human normal, malignant and cirrhotic liver tissue: in vivo and ex vivo measurements from 0.5 to 20 GHz using a precision open-ended coaxial probe.

PubMed

O'Rourke, Ann P; Lazebnik, Mariya; Bertram, John M; Converse, Mark C; Hagness, Susan C; Webster, John G; Mahvi, David M

2007-08-07

Hepatic malignancies have historically been treated with surgical resection. Due to the shortcomings of this technique, there is interest in other, less invasive, treatment modalities, such as microwave hepatic ablation. Crucial to the development of this technique is the accurate knowledge of the dielectric properties of human liver tissue at microwave frequencies. To this end, we characterized the dielectric properties of in vivo and ex vivo normal, malignant and cirrhotic human liver tissues from 0.5 to 20 GHz. Analysis of our data at 915 MHz and 2.45 GHz indicates that the dielectric properties of ex vivo malignant liver tissue are 19 to 30% higher than normal tissue. The differences in the dielectric properties of in vivo malignant and normal liver tissue are not statistically significant (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 16% higher than normal). Also, the dielectric properties of in vivo normal liver tissue at 915 MHz and 2.45 GHz are 16 to 43% higher than ex vivo. No statistically significant differences were found between the dielectric properties of in vivo and ex vivo malignant tissue (with the exception of effective conductivity at 915 MHz, where malignant tissue properties are 28% higher than normal). We report the one-pole Cole-Cole parameters for ex vivo normal, malignant and cirrhotic liver tissue in this frequency range. We observe that wideband dielectric properties of in vivo liver tissue are different from the wideband dielectric properties of ex vivo liver tissue, and that the in vivo data cannot be represented in terms of a Cole-Cole model. Further work is needed to uncover the mechanisms responsible for the observed wideband trends in the in vivo liver data.

Frequency and temperature dependent dielectric properties of TiO2-V2O5 nanocomposites

NASA Astrophysics Data System (ADS)

Ray, Apurba; Roy, Atanu; De, Sayan; Chatterjee, Souvik; Das, Sachindranath

2018-03-01

In this manuscript, we have reported the crystal structure, dielectric response, and transport phenomenon of TiO2-V2O5 nanocomposites. The nanocomposites were synthesized using a sol-gel technique having different molar ratios of Ti:V (10:10, 10:15, and 10:20). The phase composition and the morphology have been studied using X-ray diffraction and field emission scanning electron microscope, respectively. The impedance spectroscopy studies of the three samples over a wide range of temperature (50 K-300 K) have been extensively described using the internal barrier layer capacitor model. It is based on the contribution of domain and domain boundary, relaxations of the materials, which are the main crucial factors for the enhancement of the dielectric response. The frequency dependent ac conductivity of the ceramics strongly obeys the well-known Jonscher's power law, and it has been clearly explained using the theory of jump relaxation model. The temperature dependent bulk conductivity is fairly recognized to the variable-range hopping of localized polarons. The co-existence of mixed valence state of Ti ions (Ti3+ and Ti4+) in the sample significantly contributes to the change of dielectric property. The overall study of dielectric response explains that the dielectric constant and the dielectric loss are strongly dependent on temperature and frequency and decrease with an increase of frequency as well as temperature.

Effects of synthesis techniques on chemical composition, microstructure and dielectric properties of Mg-doped calcium titanate

NASA Astrophysics Data System (ADS)

Jongprateep, Oratai; Sato, Nicha

2018-04-01

Calcium titanate (CaTiO3) has been recognized as a material for fabrication of dielectric components, owing to its moderate dielectric constant and excellent microwave response. Enhancement of dielectric properties of the material can be achieved through doping, compositional and microstructural control. This study, therefore, aimed at investigating effects of powder synthesis techniques on compositions, microstructure, and dielectric properties of Mg-doped CaTiO3. Solution combustion and solid-state reaction were powder synthesis techniques employed in preparation of undoped CaTiO3 and CaTiO3 doped with 5-20 at% Mg. Compositional analysis revealed that powder synthesis techniques did not exhibit a significant effect on formation of secondary phases. When Mg concentration did not exceed 5 at%, the powders prepared by both techniques contained only a single phase. An increase of MgO secondary phase was observed as Mg concentrations increased from 10 to 20 at%. Experimental results, on the contrary, revealed that powder synthesis techniques contributed to significant differences in microstructure. Solution combustion technique produced powders with finer particle sizes, which consequently led to finer grain sizes and density enhancement. High-density specimens with fine microstructure generally exhibit improved dielectric properties. Dielectric measurements revealed that dielectric constants of all samples ranged between 231 and 327 at 1 MHz, and that superior dielectric constants were observed in samples prepared by the solution combustion technique.

Electrical conduction in polymer dielectrics

NASA Technical Reports Server (NTRS)

Cotts, D. B.

1985-01-01

The use of polymer dielectrics with moderate resistivities could reduce or eliminate problems associated with spacecraft charging. The processes responsible for conduction and the properties of electroactive polymers are reviewed, and correlations drawn between molecular structure and electrical conductivity. These structure-property relationships led to the development of several new electroactive polymer compositions and the identification of several systems that have the requisite thermal, mechanical, environmental and electrical properties for use in spacecraft.

Dielectric spectroscopy on organic charge-transfer salts

NASA Astrophysics Data System (ADS)

Lunkenheimer, P.; Loidl, A.

2015-09-01

This topical review provides an overview of the dielectric properties of a variety of organic charge-transfer salts, based on both, data reported in literature and our own experimental results. Moreover, we discuss in detail the different processes that can contribute to the dielectric response of these materials. We concentrate on the family of the 1D (TMTTF)2 X systems and the 2D BEDT-TTF-based charge-transfer salts, which in recent years have attracted considerable interest due to their often intriguing dielectric properties. We will mainly focus on the occurrence of electronic ferroelectricity in these systems, which also includes examples of multiferroicity.

Dielectric spectroscopy on organic charge-transfer salts.

PubMed

Lunkenheimer, P; Loidl, A

2015-09-23

This topical review provides an overview of the dielectric properties of a variety of organic charge-transfer salts, based on both, data reported in literature and our own experimental results. Moreover, we discuss in detail the different processes that can contribute to the dielectric response of these materials. We concentrate on the family of the 1D (TMTTF)2 X systems and the 2D BEDT-TTF-based charge-transfer salts, which in recent years have attracted considerable interest due to their often intriguing dielectric properties. We will mainly focus on the occurrence of electronic ferroelectricity in these systems, which also includes examples of multiferroicity.

Frequency and Temperature Dependent Dielectric Properties of Free-standing Strontium Titanate Thin Films.

NASA Astrophysics Data System (ADS)

Dalberth, Mark J.; Stauber, Renaud E.; Anderson, Britt; Price, John C.; Rogers, Charles T.

1998-03-01

We will report on the frequency and temperature dependence of the complex dielectric function of free-standing strontium titanate (STO) films. STO is an incipient ferroelectric with electric-field tunable dielectric properties of utility in microwave electronics. The films are grown epitaxially via pulsed laser deposition on a variety of substrates, including lanthanum aluminate (LAO), neodymium gallate (NGO), and STO. An initial film of yttrium barium cuprate (YBCO) is grown on the substrate, followed by deposition of the STO layer. Following deposition, the sacrificial YBCO layer is chemically etched away in dilute nitric acid, leaving the substrate and a released, free-standing STO film. Coplanar capacitor structures fabricated on the released films allow us to measure the dielectric response. We observe a peak dielectric function in excess of 5000 at 35K, change in dielectric constant of over a factor of 8 for 10Volt/micron electric fields, and temperature dependence above 50K that is very similar to bulk material. The dielectric loss shows two peaks, each with a thermally activated behavior, apparently arising from two types of polar defects. We will discuss the correlation between dielectric properties, growth conditions, and strain in the free-standing STO films.

Long-range coupling between ATP-binding and lever-arm regions in myosin via dielectric allostery

NASA Astrophysics Data System (ADS)

Sato, Takato; Ohnuki, Jun; Takano, Mitsunori

2017-12-01

A protein molecule is a dielectric substance, so the binding of a ligand is expected to induce dielectric response in the protein molecule, considering that ligands are charged or polar in general. We previously reported that binding of adenosine triphosphate (ATP) to molecular motor myosin actually induces such a dielectric response in myosin due to the net negative charge of ATP. By this dielectric response, referred to as "dielectric allostery," spatially separated two regions in myosin, the ATP-binding region and the actin-binding region, are allosterically coupled. In this study, from the statistically stringent analyses of the extensive molecular dynamics simulation data obtained in the ATP-free and the ATP-bound states, we show that there exists the dielectric allostery that transmits the signal of ATP binding toward the distant lever-arm region. The ATP-binding-induced electrostatic potential change observed on the surface of the main domain induced a movement of the converter subdomain from which the lever arm extends. The dielectric response was found to be caused by an underlying large-scale concerted rearrangement of the electrostatic bond network, in which highly conserved charged/polar residues are involved. Our study suggests the importance of the dielectric property for molecular machines in exerting their function.

Effect of nanocomposite gate-dielectric properties on pentacene microstructure and field-effect transistor characteristics.

PubMed

Lee, Wen-Hsi; Wang, Chun-Chieh

2010-02-01

In this study, the effect of surface energy and roughness of the nanocomposite gate dielectric on pentacene morphology and electrical properties of pentacene OTFT are reported. Nanoparticles TiO2 were added in the polyimide matrix to form a nanocomposite which has a significantly different surface characteristic from polyimide, leading to a discrepancy in the structural properties of pentacene growth. A growth mode of pentacene deposited on the nanocomposite is proposed to explain successfully the effect of surface properties of nanocomposite gate dielectric such as surface energy and roughness on the pentacene morphology and electrical properties of OTFT. To obtain the lower surface energy and smoother surface of nanocomposite gate dielectric that is responsible for the desired crystalline, microstructure of pentacene and electrical properties of device, a bottom contact OTFT-pentacene deposited on the double-layer nanocomposite gate dielectric consisting of top smoothing layer of the neat polyimide and bottom layer of (PI+ nano-TiO2 particles) nanocomposite has been successfully demonstrated to exhibit very promising performance including high current on to off ratio of about 6 x 10(5), threshold voltage of -10 V and moderately high filed mobility of 0.15 cm2V(-1)s(-1).

Molecular dynamics simulations of the dielectric properties of fructose aqueous solutions

NASA Astrophysics Data System (ADS)

Sonoda, Milton T.; Elola, M. Dolores; Skaf, Munir S.

2016-10-01

The static dielectric permittivity and dielectric relaxation properties of fructose aqueous solutions of different concentrations ranging from 1.0 to 4.0 mol l-1 are investigated by means of molecular dynamics simulations. The contributions from intra- and interspecies molecular correlations were computed individually for both the static and frequency-dependent dielectric properties, and the results were compared with the available experimental data. Simulation results in the time- and frequency-domains were analyzed and indicate that the presence of fructose has little effect on the position of the fast, high-frequency (>500 cm-1) components of the dielectric response spectrum. The low-frequency (<0.1 cm-1) components, however, are markedly influenced by sugar concentration. Our analysis indicates that fructose-fructose and fructose-water interactions strongly affect the rotational-diffusion regime of molecular motions in the solutions. Increasing fructose concentration not only enhances sugar-sugar and sugar-water low frequency contributions to the dielectric loss spectrum but also slows down the reorientational dynamics of water molecules. These results are consistent with previous computer simulations carried out for other disaccharide aqueous solutions.

Dielectric relaxation in epitaxial films of paraelectric-magnetic SrTiO3-SrMnO3 solid solution

NASA Astrophysics Data System (ADS)

Savinov, M.; Bovtun, V.; Tereshina-Chitrova, E.; Stupakov, A.; Dejneka, A.; Tyunina, M.

2018-01-01

Magneto-dielectric properties of (A2+)MnO3-type perovskites are attractive for applications and stimulate extensive studies of these materials. Here, the complex dielectric and magnetic responses are investigated as in epitaxial films of SrTi0.6Mn0.4O3, solid solution of paraelectric SrTiO3 and magnetic SrMnO3. The impedance and resonance measurements at frequencies of 10-2-1010 Hz and temperatures of 10-500 K reveal broad dielectric anomalies centered at 100-200 K, while the films are paramagnetic at all temperatures. Analysis shows polaronic electrical conductivity behind the observed behavior. Electron-phonon correlations, rather than spin-phonon correlations, are suggested to produce the apparent magneto-dielectric responses in many multiferroic manganites.

Dielectric properties, optimum formulation and microwave baking conditions of chickpea cakes.

PubMed

Alifakı, Yaşar Özlem; Şakıyan, Özge

2017-03-01

The aim of this study was to correlate dielectric properties with quality parameters, and to optimize cake formulation and baking conditions by response surface methodology. Weight loss, color, specific volume, hardness and porosity were evaluated. The samples with different DATEM (0.4, 0.8 and 1.2%) and chickpea flour concentrations (30, 40 and 50%) were baked in microwave oven at different power (300, 350, 400 W) and baking times (2.50, 3.0, 3.50 min). It was found that microwave power showed significant effect on color, while baking time showed effect on weight loss, porosity, hardness, specific volume and dielectric properties. Emulsifier level affected porosity, specific volume and dielectric constant. Chickpea flour level affected porosity, color, hardness and dielectric properties of cakes. The optimum microwave power, baking time, DATEM level and chickpea flour level were found as 400 W, 2.84 min, 1.2% and 30%, respectively. The comparison between conventionally baked and the microwave baked cakes at optimum points showed that color difference, weight loss, specific volume and porosity values of microwave baked cakes were less than those of conventionally baked cakes, on the other hand, hardness values were higher. Moreover, a negative correlation between dielectric constant and porosity, and weight loss values were detected for microwave baked samples. A negative correlation between dielectric loss factor and porosity was observed. These correlations indicated that quality characteristics of a microwave baked cake sample can be assessed from dielectric properties. These correlations provides understanding on the behavior of food material during microwave processing.

Full-time response of starch subjected to microwave heating.

PubMed

Fan, Daming; Wang, Liyun; Zhang, Nana; Xiong, Lei; Huang, Luelue; Zhao, Jianxin; Wang, Mingfu; Zhang, Hao

2017-06-21

The effect of non-ionizing microwave radiation on starch is due to a gelatinization temperature range that changes starch structure and properties. However, the changes in starch upon microwave heating are observable throughout the heating process. We compared the effects on starch heating by microwaves to the effects by rapid and regular conventional heating. Our results show that microwave heating promotes the rapid rearrangement of starch molecules at low temperatures; starch showed a stable dielectric response and a high dielectric constant. Microwave heating changed the Cole-Cole curve and the polarization of starch suspension at low temperatures. A marked transition at 2.45 GHz resulted in a double-polarization phenomenon. At temperatures below gelatinization, microwave-induced dielectric rearrangement and changes in the polarization characteristics of starch suspensions reduced the absorption properties; at temperatures above gelatinization, these characteristics became consistent with conventional heating. Throughout the heating process, microwaves change the electrical response and polarization characteristics of the starch at low temperatures, but on the macro level, there is no enhancement of the material's microwave absorption properties. In contrast, with the warming process, the starch exhibited a "blocking effect", and the absorption properties of the starch quickly returned to the level observed in conductive heating after gelatinization.

Multiple electrical phase transitions in Al substituted barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Kar, Manoranjan

2017-12-01

Barium hexaferrite is known to be a very good ferromagnetic material. However, it shows very good dielectric properties, i.e., the dielectric constant is comparable to that of the ferroelectric material. However, its crystal symmetry does not allow it to be a ferroelectric material. Hence, the electrical properties have revived the considerable research interest on these materials, not only for academic interest, but also for technological applications. There are a few reports on temperature dependent dielectric behavior of these materials. However, the exact cause of dielectric as well as electrical conductivity is yet to be established. Hence, Al (very good conducting material) substituted barium hexaferrite (BaFe12-xAlxO19, x = 0.0-4.0) has been prepared by following the modified sol-gel method to understand the ac and DC electrical properties of these materials. The crystal structure and parameters have been studied by employing the XRD and FTIR techniques. There are two transition temperatures, which have been observed in the temperature dependent ac dielectric and DC resistivity measurement. The response of dielectric behaviors to temperature is similar to that of the ferroelectric material; however, the dielectric polarization is due to the polaron hopping, which is evident from the DC resistivity analysis. Hence, the present observations lead to understand the electrical properties of barium hexaferrite. The frequency dependent dielectric dispersion can be understood by the modified Debye model. More interestingly, the dielectric constant decreases and DC resistivity increases with the increase in the Al concentration, which has the correlation between bond length modifications in the crystal due to substitution.

Atomic Layer Engineering of High-κ Ferroelectricity in 2D Perovskites.

PubMed

Li, Bao-Wen; Osada, Minoru; Kim, Yoon-Hyun; Ebina, Yasuo; Akatsuka, Kosho; Sasaki, Takayoshi

2017-08-09

Complex perovskite oxides offer tremendous potential for controlling their rich variety of electronic properties, including high-T C superconductivity, high-κ ferroelectricity, and quantum magnetism. Atomic-scale control of these intriguing properties in ultrathin perovskites is an important challenge for exploring new physics and device functionality at atomic dimensions. Here, we demonstrate atomic-scale engineering of dielectric responses using two-dimensional (2D) homologous perovskite nanosheets (Ca 2 Na m-3 Nb m O 3m+1 ; m = 3-6). In this homologous 2D material, the thickness of the perovskite layers can be incrementally controlled by changing m, and such atomic layer engineering enhances the high-κ dielectric response and local ferroelectric instability. The end member (m = 6) attains a high dielectric constant of ∼470, which is the highest among all known dielectrics in the ultrathin region (<10 nm). These results provide a new strategy for achieving high-κ ferroelectrics for use in ultrascaled high-density capacitors and post-graphene technology.

Electroactive fluorinate-based polymers: Ferroelectric and dielectric properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu Zhi; Chen Ang; Department of Physics and Department of Chemistry, University of Akron, Akron, Ohio 44325

2004-12-15

The dielectric, ferroelectric, and electroactive strain behavior of poly(vinylidene fluoride-trifluoroethylene) copolymers and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymers is studied in a wide temperature and frequency range. The dielectric response from two dielectric polarization processes, modes A(A{sup '}) and B, and the dielectric-background contribution can be identified for these polymers by using the Cole-Cole plot method. Therefore physically reasonable parameters are obtained by fitting the relaxation time to the Vogel-Fulcher relation. On the other hand, the dielectric relaxation step and high strain decrease simultaneously with decreasing temperature; this indicates that the dielectric relaxation process and high strain behavior are strongly correlated. The electron-irradiationmore » effect in copolymers and the monomer effect in terpolymers are discussed.« less

Dielectric spectroscopy of Ag-starch nanocomposite films

NASA Astrophysics Data System (ADS)

Meena; Sharma, Annu

2018-04-01

In the present work Ag-starch nanocomposite films were fabricated via chemical reduction route. The formation of Ag nanoparticles was confirmed using transmission electron microscopy (TEM). Further the effect of varying concentration of Ag nanoparticles on the dielectric properties of starch has been studied. The frequency response of dielectric constant (ε‧), dielectric loss (ε″) and dissipation factor tan(δ) has been studied in the frequency range of 100 Hz to 1 MHz. Dielectric data was further analysed using Cole-Cole plots. The dielectric constant of starch was found to be 4.4 which decreased to 2.35 in Ag-starch nanocomposite film containing 0.50 wt% of Ag nanoparticles. Such nanocomposites with low dielectric constant have potential applications in microelectronic technologies.

Dielectric behavior and transport properties of ZnO nanorods

NASA Astrophysics Data System (ADS)

Soosen Samuel, M.; Koshy, Jiji; Chandran, Anoop; George, K. C.

2011-08-01

Highly optical, good crystalline and randomly aligned ZnO nanorods were synthesized by the hydrothermal method. The dielectric properties of ZnO nanorods were attributed to the interfacial polarization at low frequencies (below 10 kHz) and orientational polarization at higher frequencies. The observed ω( n-1) dependence of dielectric loss was discussed on the basis of the Universal model of dielectric response. Dielectric loss peak was composed of the Debye like loss peak at higher frequencies and interfacial loss peak at lower frequencies. Charge transport through the grain and grain boundary region was investigated by impedance spectroscopy. At higher temperatures the conductivity of the nanorod was mainly through the grain interior and the overall impedance was contributed by the grain boundary region. The activation energy of nanorod was calculated as 0.078 eV, which is slightly higher than the reported bulk value.

Dielectric properties of doping-free NaMn{sub 7}O{sub 12}: Origin of the observed colossal dielectric constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cabassi, R.; Bolzoni, F.; Gauzzi, A.

2006-07-15

The semiconducting NaMn{sub 7}O{sub 12} is a doping-free compound with several coexistent properties such as orbital ordering, charge ordering, and magnetic orderings of different types. We investigated its dielectric response by means of frequency impedance measurements in the range from 20 Hz to 1 MHz. Standard measurements on metallized samples exhibit an apparent colossal dielectric constant (CDC) with an {epsilon}{sub R} value of several thousands at low frequencies, but a careful equivalent circuit analysis allows one to ascribe the observed CDC to the effect of a depletion layer on the metal-semiconductor junctions. We bypass this effect by means of amore » nonstandard technique employing mica linings: the resulting dielectric behavior exhibits the presence of the charge ordering transition at T{sub CO}=176 K and shows a net bulk dielectric constant value {epsilon}{sub R}{approx_equal}68 at room temperature.« less

Temperature Effects of Dielectric Properties of ER Fluids

NASA Astrophysics Data System (ADS)

Qiu, Z. Y.; Hu, L.; Liu, M. W.; Bao, H. X.; Jiang, Y. G.; Zhou, L. W.; Tang, Y.; Gao, Z.; Sun, M.; Korobko, E. V.

Under the consideration of the role that energy transfer and dissipation play in ER effect, an improved theory frame for ER effects, polarization-dissipation-structure-rheology, is suggested. The theory frame is substantiated by the basic physical laws and certain critical experimental facts. The dielectric response of a diatomite ER fluid to temperature is measured in the temperature range of 140 K to 400 K. By comparison of the DC conductivity with the AC effective conductivity of the sample, we found that the AC dielectric loss consists of two parts. One part comes from the DC conductivity, the other from the response of the bound charges in scope of particle to AC field. It is suggested that the response of bound charges is very important to ER effects. Besides, the effect of temperature on shear stress is measured, and interpreted based on the dielectric measurements. The source of two loss peaks in the curve of the dielectric loss versus temperature is not clear.

Physical and Electrical Characterization of Aluminum Polymer Capacitors

NASA Technical Reports Server (NTRS)

Liu, David; Sampson, Michael J.

2010-01-01

Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were physically examined and electrically characterized. The physical construction analysis of the capacitors revealed three different capacitor structures, i.e., traditional wound, stacked, and laminated. Electrical characterization results of polymer aluminum capacitors are reported for frequency-domain dielectric response at various temperatures, surge breakdown voltage, and other dielectric properties. The structure-property relations in polymer aluminum capacitors are discussed.

Physical and Electrical Characterization of Polymer Aluminum Capacitors

NASA Technical Reports Server (NTRS)

Liu, David; Sampson, Michael J.

2010-01-01

Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were physically examined and electrically characterized. The physical construction analysis of the capacitors revealed three different capacitor structures, i.e., traditional wound, stacked, and laminated. Electrical characterization results of polymer aluminum capacitors are reported for frequency-domain dielectric response at various temperatures, surge breakdown voltage, and other dielectric properties. The structure-property relations in polymer aluminum capacitors are discussed.

Dielectric Rheo-SANS: An Instrument for the Simultaneous Interrogation of Rheology, Microstructure and Electronic Properties of Complex Fluids

NASA Astrophysics Data System (ADS)

Wagner, Norman; Richards, Jeffrey; Hipp, Julie; Butler, Paul

In situ measurements are an increasingly important tool to inform the complex relationship between nanoscale properties and macroscopic measurements. For conducting colloidal suspensions, we seek intrinsic relationships between the measured electrical and mechanical response of a material both in quiescence and under applied shear. These relationships can be used to inform the development of new materials with enhanced electrical and mechanical performance. In order to study these relationships, we have developed a dielectric rheology instrument that is compatible with small angle neutron scattering (SANS) experiments. This Dielectric RheoSANS instrument consists of a Couette geometry mounted on an ARES G2 strain controlled rheometer enclosed in a modified Forced Convection Oven (FCO). In this talk, we outline the development of the Dielectric RheoSANS instruments and demonstrate its operation using two systems - a suspension of carbon black particles in propylene carbonate and poly(3-hexylthiophene) organogel - where there is interest in how shear influences the microstructure state of the material. By monitoring the conductivity and rheological response of these materials at the same time, we can capture the entire evolution of the material response to an applied deformation. NCNR NIST Cooperative Agreement #70NANB12H239.

Dielectric properties of graphene/MoS2 heterostructures from ab initio calculations and electron energy-loss experiments

NASA Astrophysics Data System (ADS)

Mohn, Michael J.; Hambach, Ralf; Wachsmuth, Philipp; Giorgetti, Christine; Kaiser, Ute

2018-06-01

High-energy electronic excitations of graphene and MoS2 heterostructures are investigated by momentum-resolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated using a combination of ab initio and dielectric model calculations. In particular, the layered electron-gas model is extended to thick layers by including the spatial dependence of the dielectric response in the direction perpendicular to the sheets. We apply this model to the case of graphene/MoS2/graphene heterostructures and discuss the possibility of extracting the dielectric properties of an encapsulated monolayer from measurements of the entire stack.

UV response on dielectric properties of nano nematic liquid crystal

NASA Astrophysics Data System (ADS)

Pandey, Kamal Kumar; Tripathi, Pankaj Kumar; Misra, Abhishek Kumar; Manohar, Rajiv

2018-03-01

In this work, we investigate the effect of UV light irradiation on the dielectric parameters of nematic liquid crystal (5CB) and ZnO nanoparticles dispersed liquid crystal. With addition of nanoparticles in nematic LC are promising new materials for a variety of application in energy harvesting, displays and photonics including the liquid crystal laser. To realize many applications, however we optimize the properties of liquid crystal and understand how the UV light irradiation interact the nanoparticles and LC molecules in dispersed/doped LC. The dielectric permittivity and loss factor have discussed the pure nematic LC and dispersed/doped system after, during and before UV light exposure. The dielectric relaxation spectroscopy was carried out in the frequency range 100 Hz-10 MHz in the nematic mesophase range.

K-Band Latching Switches

NASA Technical Reports Server (NTRS)

Piotrowski, W. S.; Raue, J. E.

1984-01-01

Design, development, and tests are described for two single-pole-double-throw latching waveguide ferrite switches: a K-band switch in WR-42 waveguide and a Ka-band switch in WR-28 waveguide. Both switches have structurally simple junctions, mechanically interlocked without the use of bonding materials; they are impervious to the effects of thermal, shock, and vibration stresses. Ferrite material for the Ka-band switch with a proper combination of magnetic and dielectric properties was available and resulted in excellent low loss, wideband performance. The high power handling requirement of the K-band switch limited the choice of ferrite to nickel-zinc compositions with adequate magnetic properties, but with too low relative dielectric constant. The relative dielectric constant determines the junction dimensions for given frequency responses. In this case the too low value unavoidably leads to a larger than optimum junction volume, increasing the insertion loss and restricting the operating bandwidth. Efforts to overcome the materials-related difficulties through the design of a composite junction with increased effective dielectric properties efforts to modify the relative dielectric constant of nickel-zinc ferrite are examined.

Modeling nonlinear dynamic properties of dielectric elastomers with various crosslinks, entanglements, and finite deformations

NASA Astrophysics Data System (ADS)

Zhang, Junshi; Chen, Hualing; Li, Dichen

2018-02-01

Subject to an AC voltage, dielectric elastomers (DEs) behave as a nonlinear vibration, implying potential applications as soft dynamical actuators and robots. In this article, by utilizing the Lagrange's equation, a theoretical model is deduced to investigate the dynamic performances of DEs by considering three internal properties, including crosslinks, entanglements, and finite deformations of polymer chains. Numerical calculations are employed to describe the dynamic response, stability, periodicity, and resonance properties of DEs. It is observed that the frequency and nonlinearity of dynamic response are tuned by the internal properties of DEs. Phase paths and Poincaré maps are utilized to detect the stability and periodicity of the nonlinear vibrations of DEs, which demonstrate that transitions between aperiodic and quasi-periodic vibrations may occur when the three internal properties vary. The resonance of DEs involving the three internal properties of polymer chains is also investigated.

Exploratory studies of new avenues to achieve high electromechanical response and high dielectric constant in polymeric materials

NASA Astrophysics Data System (ADS)

Huang, Cheng

High performance soft electronic materials are key elements in advanced electronic devices for broad range applications including capacitors, actuators, artificial muscles and organs, smart materials and structures, microelectromechanical (MEMS) and microfluidic devices, acoustic devices and sensors. This thesis exploits new approaches to improve the electromechanical response and dielectric response of these materials. By making use of novel material phenomena such as large anisotropy in dipolar response in liquid crystals (LCs) and all-organic composites in which high dielectric constant organic solids and conductive polymers are either physically blended into or chemically grafted to a polymer matrix, we demonstrate that high dielectric constant and high electromechanical conversion efficiency comparable to that in ceramic materials can be achieved. Nano-composite approach can also be utilized to improve the performance of the electronic electroactive polymers (EAPs) and composites, for example, exchange coupling between the fillers and matrix with very large dielectric contrast can lead to significantly enhance the dielectric response as well as electromechanical response when the heterogeneity size of the composite is comparable to the exchange length. In addition to the dielectric composites, in which high dielectric constant fillers raise the dielectric constant of composites, conductive percolation can also lead to high dielectric constant in polymeric materials. An all-polymer percolative composite is introduced which exhibits very high dielectric constant (>7,000). The flexible all-polymer composites with a high dielectric constant make it possible to induce a high electromechanical response under a much reduced electric field in the field effect electroactive polymer (EAP) actuators (a strain of 2.65% with an elastic energy density of 0.18 J/cm3 can be achieved under a field of 16 V/mum). Agglomeration of the particles can also be effectively prevented by in situ preparation. High dielectric constant copper phthalocyanine oligomer and conductive polyaniline oligomer were successfully bonded to polyurethane backbone to form fully functionalized nano-phase polymers. Improvement of dispersibility of oligomers in polymer matrix makes the system self-organize the nanocomposites possessing oligomer nanophase (below 30nm) within the fully functionalized polymers. The resulting nanophase polymers significantly enhance the interface effect, which through the exchange coupling raises the dielectric response markedly above that expected from simple mixing rules for dielectric composites. Consequently, these nano-phase polymers offer a high dielectric constant (a dielectric constant near 1,000 at 20 Hz), improve the breakdown field and mechanical properties, and exhibit high electromechanical response. A longitudinal strain of more than -14% can be induced under a much reduced field, 23 V/mum, with an elastic energy density of higher than 1 J/cm3. The elastic modulus is as high as 100MPa, and a transverse strain is 7% under the same field. (Abstract shortened by UMI.)

Intrinsic dielectric properties of magnetodielectric La2CoMnO6

NASA Astrophysics Data System (ADS)

Silva, R. X.; Moreira, R. L.; Almeida, R. M.; Paniago, R.; Paschoal, C. W. A.

2015-06-01

Manganite with a double perovskite structure is an attractive material because of its interesting magnetoelectric and dielectric responses. In particular, colossal dielectric constant (CDC) behavior has been observed in La2CoMnO6 (LCMO) at radio frequencies and at room temperature. In this paper, we used infrared-reflectivity spectroscopy to study a LCMO ceramic obtained through a modified Pechini's method to determine the phonon contribution to the intrinsic dielectric response of the system and to investigate the CDC origin. The analysis of the main polar modes and of the obtained phonon parameters indicate that the CDC effect of LCMO is of pure extrinsic origin. In addition, we estimated the dielectric constant and the quality factor of the material in the microwave region to be ɛ's ˜ 16 and Qu × f ˜ 124 THz, which verifies that LCMO is appropriate for application in microwave devices and circuitry.

Influence of Clay Content, Mineralogy and Fabric On Radar Frequency Response of Aquifer Materials

NASA Astrophysics Data System (ADS)

West, L. J.; Handley, K.

High frequency electromagnetic methods such as ground penetrating radar (GPR) and time domain reflectometry (TDR) are widely employed to measure water saturation in the vadose zone and water filled porosity in the saturated zone. However, previous work has shown that radar frequency dielectric properties are strongly influenced by clay as well as by water content. They have also shown that that the dielectric response of clay minerals is strongly frequency dependent, and that even a small proportion of clay such as that present in many sandstone aquifers can have a large effect at typi- cal GPR frequencies (around 100MHz). Hence accurate water content/porosity deter- mination requires clay type and content to be taken into account. Reported here are dielectric measurements on clay-sand mixtures, aimed at investigating the influence of clay mineralogy, particle shape, and the geometrical arrangement of the mixture constituents on GPR and TDR response. Dielectric permittivity (at 50-1000MHz) was measured for mixtures of Ottawa Sand and various clay minerals or clay size quartz rock flour, using a specially constructed dielectric cell. Both homogeneous and layered mixtures were tested. The influence of pore water salinity, clay type, and particle arrangement on the dielectric response is interpreted in terms of dielectric dispersion mechanisms. The appropriateness of var- ious dielectric mixing rules such as the Complex Refractive Index Method (CRIM) for determination of water content or porosity from field GPR and TDR data are dis- cussed.

Plant Water Stress Detection Using Radar: The Influence Of Water Stress On Leaf Dielectric Properties

NASA Astrophysics Data System (ADS)

van Emmerik, Tim; Steele-Dunne, Susan; Judge, Jasmeet; van de Giesen, Nick

2015-04-01

Recent research on an agricultural maize canopy has demonstrated that leaf water content can change considerably during the day and in response to water stress. Model simulations suggest that these changes have a significant impact on radar backscatter, particularly in times of water stress. Radar is already used for several vegetation and soil monitoring applications, and might be used for water stress detection in agricultural canopies. Radar observations of the land surface are sensitive because it results in two-way attenuation of the reflected signal from the soil surface, and vegetation contributes to total backscatter from the canopy itself. An important driver that determines the impact of vegetation on backscatter is the dielectric constant of the leaves, which is primarily a function of their moisture content. Understanding the effects of water stress on the dynamics of leaf dielectric properties might shed light on how radar can be used to detect vegetation water stress. Previous studies have investigated the dielectric properties of vegetation. However, this has mainly been done using destructive sampling or in-vivo measurements of tree trunks. Unfortunately, few in-vivo measurements of leaf dielectric properties exist. This study presents datasets of in-vivo dielectric measurements of maize leaves, taken during two field experiments. One experiment was done using was done during a period of water stress, the other during a period without. Field measurements revealed a different vertical profile in dielectric properties for the period with and without water stress. During a period of increased water stress, the diurnal dynamics of leaves at different heights responded differently to a decrease in bulk moisture content. This study provides insight in the effect of water stress on leaf dielectric properties and water content, and highlights the potential use of radar for water stress detection in agricultural canopies.

Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minami, Yasuo; Horiuchi, Kohei; Masuda, Kaisei

We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si platemore » was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.« less

Effect of organo-clay on the dielectric relaxation response of silicone rubber

NASA Astrophysics Data System (ADS)

Gharavi, N.; Razzaghi-Kashani, M.; Golshan-Ebrahimi, N.

2010-02-01

Dielectric elastomers are light weight, low-cost, highly deformable and fast response smart materials capable of converting electrical energy into mechanical work or vice versa. Silicone rubber is a well-known dielectric elastomer which is used as actuator, and in order to enhance the efficiency of this smart material, compounding of silicone rubber with various fillers can be carried out. The effect of organically modified montmorillonite (OMMT) nano-clay on improvement of dielectric properties, actuation stress and its relaxation response was considered in this study. OMMT was dispersed in room temperature vulcanized (RTV) silicone rubber, and a composite film was cast. Using an in-house actuation set-up, it was shown that the actuation stress for a given electric field intensity is higher for composites than that for pristine silicone rubber. Also, the time-dependent actuation response of the samples was evaluated, and it was shown that the characteristic relaxation time of the actuation stress for composites is less than for the pristine rubber as a result of OMMT addition.

Spacecraft dielectric material properties and spacecraft charging

NASA Technical Reports Server (NTRS)

Frederickson, A. R.; Wall, J. A.; Cotts, D. B.; Bouquet, F. L.

1986-01-01

The physics of spacecraft charging is reviewed, and criteria for selecting and testing semiinsulating polymers (SIPs) to avoid charging are discussed and illustrated. Chapters are devoted to the required properties of dielectric materials, the charging process, discharge-pulse phenomena, design for minimum pulse size, design to prevent pulses, conduction in polymers, evaluation of SIPs that might prevent spacecraft charging, and the general response of dielectrics to space radiation. SIPs characterized include polyimides, fluorocarbons, thermoplastic polyesters, poly(alkanes), vinyl polymers and acrylates, polymers containing phthalocyanine, polyacene quinones, coordination polymers containing metal ions, conjugated-backbone polymers, and 'metallic' conducting polymers. Tables summarizing the results of SIP radiation tests (such as those performed for the NASA Galileo Project) are included.

Exploring the Room-Temperature Ferromagnetism and Temperature-Dependent Dielectric Properties of Sr/Ni-Doped LaFeO3 Nanoparticles Synthesized by Reverse Micelle Method

NASA Astrophysics Data System (ADS)

Naseem, Swaleha; Khan, Shakeel; Husain, Shahid; Khan, Wasi

2018-03-01

This paper reports the thermal, microstructural, dielectric and magnetic properties of La0.75Sr0.25Fe0.65Ni0.35O3 nanoparticles (NPs) synthesized via reverse micelle technique. The thermogravimetric analysis of as-prepared NPs confirmed a good thermal stability of the sample. Powder x-ray diffraction data analyzed with a Rietveld refinement technique revealed single-phase and orthorhombic distorted perovskite crystal structure of the NPs having Pbnm space group. The transmission electron microscopy images show the crystalline nature and formation of nanostructures with a fairly uniform distribution of particles throughout the sample. Temperature-dependent dielectric properties of the NPs in accordance with the Kramers-Kronig transformation (KKT) model, universal dielectric response model and jump relaxation model have been discussed. Electrode or interface polarization is likely the cause of the observed dielectric behavior. Due to grain boundaries and Schottky barriers of the metallic electrodes of semiconductors, the depletion region is observed, which gives rise to Maxwell-Wagner relaxation and hence high dielectric constants. Magnetic studies revealed the ferromagnetic nature of the prepared NPs upon Sr and Ni doping in LaFeO3 perovskite at room temperature. Therefore, these NPs could be a potential candidate as electrode material in solid oxide fuel cells.

Dielectric and Nonohmic Properties of CaCu3Ti4O12/SrTiO3 Ceramics

NASA Astrophysics Data System (ADS)

Xue, Renzhong; Liu, Dewei; Chen, Zhenping; Dai, Haiyang; Chen, Jing; Zhao, Gaoyang

2015-04-01

In this work, (1 - x)CaCu3Ti4O12- xSrTiO3 [(1 - x)CCTO/ xST, x = 0% to 2%] ceramic samples were prepared by the solid-state reaction method. The dielectric and electrical properties of CaCu3Ti4O12 (CCTO) and CaCu3Ti4O12/SrTiO3 (CCTO/ST) ceramics were investigated. The results show that a small amount of Sr2+ can enter the lattice of CCTO. The mean grain size of the ceramic samples increased greatly for x = 0.5% and then decreased for x = 0.75% to 2%. ST addition and Sr2+ preferential occupancy in CCTO grains should be responsible for the change of the microstructure. Interestingly, the dielectric constant ( ɛ) of the 0.5% ST-added sample increased significantly while the dielectric loss (tan δ) remained low. With further increase of the ST content, the ɛ and tan δ values of the CCTO ceramics decreased monotonically while the nonlinear current-voltage properties were significantly enhanced. The change in the potential barrier height is thought to be the main cause for the opposite behaviors in the dielectric properties and nonohmic characteristics.

Influence of applied electric field annealing on the microwave properties of (Ba0.5Sr0.5)TiO3 thin films

NASA Astrophysics Data System (ADS)

Cho, Kwang-Hwan; Lee, Chil-Hyoung; Kang, Chong-Yun; Yoon, Seok-Jin; Lee, Young-Pak

2007-04-01

The effect of heat treatment in electric field on the structure and dielectric properties at microwave range of rf magnetron sputtering derived (Ba0.5Sr0.5)TiO3 thin films have been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability. The increased out-of-plane lattice constant in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature. And in dielectric loss, as the Ti-O bonding lengths increase, the energy scattering on the ferroelectric mode also increases. So, the value of dielectric loss is slightly increased.

The contribution of 180° domain wall motion to dielectric properties quantified from in situ X-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fancher, C. M.; Brewer, S.; Chung, C. C.

2017-03-01

The contribution of 180° domain wall motion to polarization and dielectric properties of ferroelectric materials has yet to be determined experimentally. In this paper, an approach for estimating the extent of (180°) domain reversal during application of electric fields is presented. We demonstrate this method by determining the contribution of domain reversal to polarization in soft lead zirconate titanate during application of strong electric fields. At the maximum applied field, domain reversal was determined to account for >80% of the measured macroscopic polarization. We also apply the method to quantify the contribution of domain reversal to the weak-field dielectric permittivitymore » of BaTiO 3. The results of this analysis determined that domain reversal accounts for up to ~70% of the macroscopic dielectric permittivity in BaTiO 3. These results demonstrate the predominance of domain reversal to high and low-field dielectric response in ferroelectric polycrystalline materials.« less

Extrinsic contributions to the dielectric response in sintered BaTiO3 nanostructures in paraelectric and ferroelectric regimes

NASA Astrophysics Data System (ADS)

Jaffari, G. Hassnain; Rehman, Atiq ur; Iqbal, Asad M.; Awan, M. S.; Saleemi, Mohsin

2017-11-01

Post sintering studies of BaTiO3 (BTO) nanoparticles are presented in detail. Bulk nanostructures were prepared via three different compaction processes, namely, uniaxial cold pressing (UCP), Cold Isostatic Pressing (CIP) and Spark Plasma Sintering (SPS). Effect of compaction technique on microstructures have been investigated and correlated with electrical response for each sample. In addition to the transport properties, temperature and frequency dependent dielectric response of variously sintered samples and bulk counterpart was recorded. Several aspects have been identified that are essential to be taken into account in order to completely understand physical processes. Drastically distinct features were observed in paraelectric (PE) regime well above ferroelectric (FE)-PE transition temperature. These features include intra grain conduction with a reduction in the magnitude of PE to FE peak dielectric constant magnitude. Role of strain, grain boundary conduction associated with observation of Maxwell Wagner relaxation and hopping conduction in dielectric and ferroelectric response have been observed and discussed. Densification with presence of oxygen vacancies, significantly enhances conductivity associated with the hopping of the carriers, in turn deteriorated ferroelectric response.

Development of dielectric elastomer nanocomposites as stretchable actuating materials

NASA Astrophysics Data System (ADS)

Wang, Yu; Sun, L. Z.

2017-10-01

Dielectric elastomer nanocomposites (DENCs) filled with multi-walled carbon nanotubes are developed. The electromechanical responses of DENCs to applied electric fields are investigated through laser Doppler vibrometry. It is found that a small amount of carbon nanotube fillers can effectively enhance the electromechanical performance of DENCs. The enhanced electromechanical properties have shown not only that the desired thickness strain can be achieved with reduced required electric fields but also that significantly large thickness strain can be obtained with any electric fields compared to pristine dielectric elastomers.

Effect of Zn doping on structural, magnetic and dielectric properties of LaFeO{sub 3} synthesized through sol–gel auto-combustion process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, Irshad; Husain, Shahid, E-mail: s.husain@lycos.com; Khan, Wasi

2013-11-15

Graphical abstract: - Highlights: • We have synthesized the samples of LaFe{sub 1−x}Zn{sub x}O{sub 3} (0 ≤ x ≤ 0.3) using sol–gel auto-combustion process. • The doping of Zn{sup 2+} hugely enhances the dielectric constant (ε′) and it shows a colossal value. • The parent compound LaFeO{sub 3} does not show any relaxation peak, but the substitution of Zn at Fe{sup 3+} site brings the relaxation in the system. • The system shows a peak behavior thereby giving the Debye like dipolar relaxation response. - Abstract: We have studied the structural and dielectric properties of nano-crystalline LaFe{sub 1−x}Zn{sub x}O{sub 3}more » (0 ≤ x ≤ 0.3) pervoskite samples synthesized through sol–gel auto-combustion technique. X-ray diffraction and FTIR spectroscopy are used to confirm the single phase characteristics. Microstructural features are investigated using scanning electron microscope and compositional analysis is performed through energy dispersive spectroscopy. The average grain sizes, calculated from the Scherrer formula, lie in the range below 30 nm. The hysteresis (M-H) curves display a weak magnetic order and a shift in the hysteresis loops. Dielectric response has been discussed, in the framework of “universal dielectric response” model. The value of dielectric constant (ε′) increases drastically on Zn doping. The dielectric loss factor (ε″) shows Debye like dipolar relaxation behavior. The observed peaks in loss factor (ε″) are attributed to the fact that a strong correlation between the conduction mechanism and the dielectric behavior exists in ferrites.« less

Applying Broadband Dielectric Spectroscopy (BDS) for the Biophysical Characterization of Mammalian Tissues under a Variety of Cellular Stresses

PubMed Central

Souli, Maria P.; Klonos, Panagiotis; Fragopoulou, Adamantia F.; Mavragani, Ifigeneia V.; Pateras, Ioannis S.; Kostomitsopoulos, Nikolaos; Margaritis, Lukas H.; Zoumpoulis, Pavlos; Kaklamanis, Loukas; Kletsas, Dimitris; Gorgoulis, Vassilis G.; Kyritsis, Apostolos; Pissis, Polycarpos; Georgakilas, Alexandros G.

2017-01-01

The dielectric properties of biological tissues can contribute non-invasively to a better characterization and understanding of the structural properties and physiology of living organisms. The question we asked, is whether these induced changes are effected by an endogenous or exogenous cellular stress, and can they be detected non-invasively in the form of a dielectric response, e.g., an AC conductivity switch in the broadband frequency spectrum. This study constitutes the first methodological approach for the detection of environmental stress-induced damage in mammalian tissues by the means of broadband dielectric spectroscopy (BDS) at the frequencies of 1–106 Hz. Firstly, we used non-ionizing (NIR) and ionizing radiation (IR) as a typical environmental stress. Specifically, rats were exposed to either digital enhanced cordless telecommunication (DECT) radio frequency electromagnetic radiation or to γ-radiation, respectively. The other type of stress, characterized usually by high genomic instability, was the pathophysiological state of human cancer (lung and prostate). Analyzing the results of isothermal dielectric measurements provided information on the tissues’ water fraction. In most cases, our methodology proved sufficient in detecting structural changes, especially in the case of IR and malignancy. Useful specific dielectric response patterns are detected and correlated with each type of stress. Our results point towards the development of a dielectric-based methodology for better understanding and, in a relatively invasive way, the biological and structural changes effected by radiation and developing lung or prostate cancer often associated with genomic instability. PMID:28420124

Aggregate linear properties of ferroelectric ceramics and polycrystalline thin films: Calculation by the method of effective piezoelectric medium

NASA Astrophysics Data System (ADS)

Pertsev, N. A.; Zembilgotov, A. G.; Waser, R.

1998-08-01

The effective dielectric, piezoelectric, and elastic constants of polycrystalline ferroelectric materials are calculated from single-crystal data by an advanced method of effective medium, which takes into account the piezoelectric interactions between grains in full measure. For bulk BaTiO3 and PbTiO3 polarized ceramics, the dependences of material constants on the remanent polarization are reported. Dielectric and elastic constants are computed also for unpolarized c- and a-textured ferroelectric thin films deposited on cubic or amorphous substrates. It is found that the dielectric properties of BaTiO3 and PbTiO3 polycrystalline thin films strongly depend on the type of crystal texture. The influence of two-dimensional clamping by the substrate on the dielectric and piezoelectric responses of polarized films is described quantitatively and shown to be especially important for the piezoelectric charge coefficient of BaTiO3 films.

Investigation of dielectric properties of different cake formulations during microwave and infrared-microwave combination baking.

PubMed

Sakiyan, Ozge; Sumnu, Gulum; Sahin, Serpil; Meda, Venkatesh

2007-05-01

Dielectric properties can be used to understand the behavior of food materials during microwave processing. Dielectric properties influence the level of interaction between food and high frequency electromagnetic energy. Dielectric properties are, therefore, important in the design of foods intended for microwave preparation. In this study, it was aimed to determine the variation of dielectric properties of different cake formulations during baking in microwave and infrared-microwave combination oven. In addition, the effects of formulation and temperature on dielectric properties of cake batter were examined. Dielectric constant and loss factor of cake samples were shown to be dependent on formulation, baking time, and temperature. The increase in baking time and temperature decreased dielectric constant and loss factor of all formulations. Fat content was shown to increase dielectric constant and loss factor of cakes.

Dielectric nanoresonators for light manipulation

NASA Astrophysics Data System (ADS)

Yang, Zhong-Jian; Jiang, Ruibin; Zhuo, Xiaolu; Xie, Ya-Ming; Wang, Jianfang; Lin, Hai-Qing

2017-07-01

Nanostructures made of dielectric materials with high or moderate refractive indexes can support strong electric and magnetic resonances in the optical region. They can therefore function as nanoresonators. In addition to plasmonic metal nanostructures that have been widely investigated, dielectric nanoresonators provide a new type of building blocks for realizing powerful and versatile nanoscale light manipulation. In contrast to plasmonic metal nanostructures, nanoresonators made of appropriate dielectric materials are low-cost, earth-abundant and have very small or even negligible light energy losses. As a result, they will find potential applications in a number of photonic devices, especially those that require low energy losses. In this review, we describe the recent progress on the experimental and theoretical studies of dielectric nanoresonators. We start from the basic theory of the electromagnetic responses of dielectric nanoresonators and their fabrication methods. The optical properties of individual dielectric nanoresonators are then elaborated, followed by the coupling behaviors between dielectric nanoresonators, between dielectric nanoresonators and substrates, and between dielectric nanoresonators and plasmonic metal nanostructures. The applications of dielectric nanoresonators are further described. Finally, the challenges and opportunities in this field are discussed.

Improved flexoelectricity in PVDF/barium strontium titanate (BST) nanocomposites

NASA Astrophysics Data System (ADS)

Hu, Xinping; Zhou, Yang; Liu, Jie; Chu, Baojin

2018-04-01

The flexoelectric effect of polymers is normally much weaker than that of ferroelectric oxides. In order to improve the flexoelectric response of the poly(vinylidene fluoride) (PVDF) ferroelectric polymer, PVDF/Ba0.67Si0.33TiO3 (BST) nanocomposites were fabricated. BST nanofibers were prepared by the electrospinning method, and the fibers were further surface modified with H2O2 to achieve a stronger interfacial interaction between the fibers and polymer matrix. Due to the high dielectric properties and strong flexoelectric effect of the BST, both dielectric constant and flexoelectric response of the composite with 25 vol. % surface modified BST are 3-4 times higher than those of PVDF. The dependence of the dielectric constant and the flexoelectric coefficient on the composition of the nanocomposites can be fitted by the empirical Yamada model, and the dielectric constant and the flexoelectric coefficient are correlated by a linear relationship. This study provides an approach to enhance the flexoelectric response of PVDF-based polymers.

Tunable optical response at the plasmon-polariton frequency in dielectric-graphene-metamaterial systems

NASA Astrophysics Data System (ADS)

Calvo-Velasco, D. M.; Porras-Montenegro, N.

2018-04-01

By using the scattering matrix formalism, it is studied the optical properties of one dimensional photonic crystals made of multiple layers of dielectric and uniaxial anisotropic single negative electric metamaterial with Drude type responses, with inclusions of graphene in between the dielectric-dielectric interfaces (DGMPC). The transmission spectra for transverse electric (TE) and magnetic (TM) polarization are presented as a function of the incidence angle, the graphene chemical potential, and the metamaterial plasma frequencies. It is found for the TM polarization the tunability of the DGMPC optical response with the graphene chemical potential, which can be observed by means of transmission or reflexion bands around the metamaterial plasmon-polariton frequency, with bandwidths depending on both the incidence angle and the metamaterial plasma frequency. Also, the transmission band is observed when losses in the metamaterial slabs are considered for finite systems. The conditions for the appearance of these bands are shown analytically. We consider this work contributes to open new possibilities to the design of photonic devices with DGMPCs.

Colossal dielectric constant in PrFeO 3 semiconductor ceramics

NASA Astrophysics Data System (ADS)

Prasad, Bandi Vittal; Rao, G. Narsinga; Chen, J. W.; Babu, D. Suresh

2012-02-01

The perovskite PrFeO 3 ceramics were synthesized via sol-gel method. The dielectric properties and impedance spectroscopy (IS) of these ceramics were studied in the frequency range from 100 Hz to 1000 kHz in the temperature range from 80 K to 300 K. These materials exhibited colossal dielectric constant value of ˜10 4 at room temperature. The response is similar to that observed for relaxorferroelectrics. IS data analysis indicates the ceramics to be electrically heterogeneous semiconductor consisting of semiconducting grains with dielectric constant 30 and more resistive grain boundaries with effective dielectric constant ˜10 4. We conclude, therefore that grain boundary effect is the primary source for the high effective permittivity in PrFeO 3 ceramics.

Effect of SiO2 grafted MWCNTs on the mechanical and dielectric properties of PEN composite films

NASA Astrophysics Data System (ADS)

Jin, Fei; Feng, Mengna; Huang, Xu; Long, Cheng; Jia, Kun; Liu, Xiaobo

2015-12-01

In this study, the functional poly (arylene ether nitrile) (PEN)/multiwall carbon nanotubes (MWCNTs)/SiO2 nanocomposite with high mechanical and good electrical properties were fabricated through a simple and effective method. Specifically, the surface modification using highly ordered and porous SiO2 not only improves the dispersion of the MWCNTs in polymer matrix, but also combines the excellent properties of SiO2 and MWCNTs. Transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), and scanning electron microscope (SEM) were employed to confirm the surface functionalization of MWCNTs. As a result, all the composite films exhibited good dielectric properties with high dielectric constant of 7 as well as low dielectric loss of 0.04. Besides, the results of mechanical tests showed that the tensile strength and modulus reached their highest values at the 2 wt% MWCNTs-SiO2 loading content (125 MPa and 2950 MPa, respectively). The rheological results showed that MWCNTs-SiO2/PEN composites have a typical solid-like viscoelastic response as frequencies changes. Therefore, all the results revealed that surface functionalization has strong influence on the dispersion state of MWCNTs in PEN matrix.

Dielectric tunability of vertically aligned ferroelectric-metal oxide nanocomposite films controlled by out-of-plane misfit strain

NASA Astrophysics Data System (ADS)

Wu, Huaping; Ma, Xuefu; Zhang, Zheng; Zhu, Jun; Wang, Jie; Chai, Guozhong

2016-04-01

A nonlinear thermodynamic model based on the vertically aligned nanocomposite (VAN) thin films of ferroelectric-metal oxide system has been developed to investigate the physical properties of the epitaxial Ba0.6Sr0.4TiO3 (BST) films containing vertical Sm2O3 (SmO) nanopillar arrays on the SrTiO3 substrate. The phase diagrams of out-of-plane lattice mismatch vs. volume fraction of SmO are calculated by minimizing the total free energy. It is found that the phase transformation and dielectric response of BST-SmO VAN systems are extremely dependent on the in-plane misfit strain, the out-of-plane lattice mismatch, the volume fraction of SmO phase, and the external electric field applied to the nanocomposite films at room temperature. In particular, the BST-SmO VAN systems exhibit higher dielectric properties than pure BST films. Giant dielectric response and maximum tunability are obtained near the lattice mismatch where the phase transition occurs. Under the in-plane misfit strain of umf=0.3 % and the out-of-plane lattice mismatch of u3=0.002 , the dielectric tunability can be dramatically enhanced to 90% with the increase of SmO volume fraction, which is well consistent with previous experimental results. This work represents an approach to further understand the dependence of physical properties on the lattice mismatch (in-plane and out-of-plane) and volume fraction, and to manipulate or optimize functionalities in the nanocomposite oxide thin films.

Temperature dependent x-ray diffraction and dielectric studies of multiferroic GaFeO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Rajeev; Mall, Ashish Kumar, E-mail: ashishm@iitk.ac.in; Gupta, Rajeev

2016-05-06

Polycrystalline GaFeO{sub 3} (GFO) samples were synthesized by sol-gel method. The structural and dielectric properties of GaFeO{sub 3} ceramic have been investigated by a combination of XRD and permittivity measurement. The X-ray diffraction spectra shows single phase orthorhombically distorted perovskite structure with Pc2{sub 1}n symmetry over a wide range of temperature 300 K to 600 K, with no evidence of any phase transition. Refined lattice parameters (a, b, c and V) increases with increasing temperature. Temperature dependent dielectric properties were investigated in the frequency range from 100Hz–5MHz. Impedance spectroscopy study on the sample showed that the dielectric constant and acmore » conductivity with frequency increases on increasing the temperature. Cole-Cole plots suggest that the response from grain is dominant at low temperature whereas grain boundary response overcomes as temperature increases. The relaxation activation energy (calculated from Cole-Cole plots) value is found to be 0.32 eV for the grain boundary. We believe that the oxygen ion vacancies play an important role in conduction processes at higher temperatures.« less

Nonlinear dielectric effects in liquids: a guided tour

NASA Astrophysics Data System (ADS)

Richert, Ranko

2017-09-01

Dielectric relaxation measurements probe how the polarization of a material responds to the application of an external electric field, providing information on structure and dynamics of the sample. In the limit of small fields and thus linear response, such experiments reveal the properties of the material in the same thermodynamic state it would have in the absence of the external field. At sufficiently high fields, reversible changes in enthalpy and entropy of the system occur even at constant temperature, and these will in turn alter the polarization responses. The resulting nonlinear dielectric effects feature field induced suppressions (saturation) and enhancements (chemical effect) of the amplitudes, as well as time constant shifts towards faster (energy absorption) and slower (entropy reduction) dynamics. This review focuses on the effects of high electric fields that are reversible and observed at constant temperature for single component glass-forming liquids. The experimental challenges involved in nonlinear dielectric experiments, the approaches to separating and identifying the different sources of nonlinear behavior, and the current understanding of how high electric fields affect dielectric materials will be discussed. Covering studies from Debye’s initial approach to the present state-of-the-art, it will be emphasized what insight can be gained from the nonlinear responses that are not available from dielectric relaxation results obtained in the linear regime.

The enhancement in dielectric and magnetic property in Na and Mn co substituted lanthanum ferrite

NASA Astrophysics Data System (ADS)

Rai, Atma; Thakur, Awalendra K.

2016-05-01

Nanocrystalline solid solutions of La1-xNaxFe1-yMnyO3 (x=y=0.00 and 0.25) were prepared via modified Pechini route. No evidence of secondary or impurity phase has been detected up to the detection of error limit of high power X-ray diffractometer. Dielectric property of the samples has been investigated in the frequency range 100 Hz-4MHz at temperature ranging 300-450K. The value of relative permittivity (ɛr) increases drastically and shows colossal dielectric response (˜104) by cosubstitution of Na and Mn as compared to pure LaFeO3. Dielectric relaxation peak in loss tangent in both samples have been found and shift towards higher frequency region as temperature increases. Magnetization-Field (M-H) loop of the calcined sample have been recorded at room temperature (300K) at field ±60kOe. Magnetic property also enhanced by co substitution of Na and Mn. The change in Fe/Mn-O-Fe/Mn angle by co-substitution of Na and Mn in LaFeO3 and indirect exchange interaction between two different magnetic sub lattices Fe and Mn might be responsible for drastic change. Saturation/maximum magnetic moment increase ˜four times in LNFM25 (5.335emu/g) as compared to pure LaFeO3 (1.302emu/g).

Hydration properties of adenosine phosphate series as studied by microwave dielectric spectroscopy.

PubMed

Mogami, George; Wazawa, Tetsuichi; Morimoto, Nobuyuki; Kodama, Takao; Suzuki, Makoto

2011-02-01

Hydration properties of adenine nucleotides and orthophosphate (Pi) in aqueous solutions adjusted to pH=8 with NaOH were studied by high-resolution microwave dielectric relaxation (DR) spectroscopy at 20 °C. The dielectric spectra were analyzed using a mixture theory combined with a least-squares Debye decomposition method. Solutions of Pi and adenine nucleotides showed qualitatively similar dielectric properties described by two Debye components. One component was characterized by a relaxation frequency (f(c)=18.8-19.7 GHz) significantly higher than that of bulk water (17 GHz) and the other by a much lower f(c) (6.4-7.6 GHz), which are referred to here as hyper-mobile water and constrained water, respectively. By contrast, a hydration shell of only the latter type was found for adenosine (f(c)~6.7 GHz). The present results indicate that phosphoryl groups are mostly responsible for affecting the structure of the water surrounding the adenine nucleotides by forming one constrained water layer and an additional three or four layers of hyper-mobile water. Copyright © 2010 Elsevier B.V. All rights reserved.

Ultrasonic synthesis of In-doped SnS nanoparticles and their physical properties

NASA Astrophysics Data System (ADS)

Jamali-Sheini, Farid; Cheraghizade, Mohsen; Yousefi, Ramin

2018-05-01

Indium (In)-doped Tin (II) Sulfide (SnS) nanoparticles (NPs) were synthesized by an ultra-sonication method and their optical, electrical, dielectric and photocatalytic properties were investigated. XRD patterns of the obtained NPs indicated formation of orthorhombic polycrystalline SnS. Field emission scanning electron microscopy exhibited flower-like NPs with particle sizes below 100 nm for both SnS and In-doped SnS samples. Optical analysis showed a decrease in energy band gap of SnS NPs upon In doping. In addition, electrical results demonstrated p-type nature of the synthesized SnS NPs and enhanced electrical conductivity of the NPs due to increased tin vacancy. Dielectric experiments on SnS NPs suggested an electronic polarizations effect to be responsible for changing dielectric properties of the particles, in terms of frequency. Finally, photocatalytic experiments revealed that high degradation power can be obtained using In-doped SnS NPs.

Significantly Elevated Dielectric and Energy Storage Traits in Boron Nitride Filled Polymer Nano-composites with Topological Structure

NASA Astrophysics Data System (ADS)

Feng, Yefeng; Zhang, Jianxiong; Hu, Jianbing; Li, Shichun; Peng, Cheng

2018-03-01

Interface induced polarization has a prominent influence on dielectric properties of 0-3 type polymer based composites containing Si-based semi-conductors. The disadvantages of composites were higher dielectric loss, lower breakdown strength and energy storage density, although higher permittivity was achieved. In this work, dielectric, conductive, breakdown and energy storage properties of four nano-composites have been researched. Based on the cooperation of fluoropolymer/alpha-SiC layer and fluoropolymer/hexagonal-BN layer, it was confirmed constructing the heterogeneous layer-by-layer composite structure rather than homogeneous mono-layer structure could significantly reduce dielectric loss, promote breakdown strength and increase energy storage density. The former worked for a larger dielectric response and the latter layer acted as a robust barrier of charge carrier transfer. The best nano-composite could possess a permittivity of 43@100 Hz ( 3.3 times of polymer), loss of 0.07@100 Hz ( 37% of polymer), discharged energy density of 2.23 J/cm3@249 kV/cm ( 10 times of polymer) and discharged energy efficiency of 54%@249 kV/cm ( 5 times of polymer). This work might enlighten a facile route to achieve the promising high energy storage composite dielectrics by constructing the layer-by-layer topological structure.

Evaluation of the influence of the internal aqueous solvent structure on electrostatic interactions at the protein-solvent interface by nonlocal continuum electrostatic approach.

PubMed

Rubinstein, Alexander; Sherman, Simon

The dielectric properties of the polar solvent on the protein-solvent interface at small intercharge distances are still poorly explored. To deconvolute this problem and to evaluate the pair-wise electrostatic interaction (PEI) energies of the point charges located at the protein-solvent interface we used a nonlocal (NL) electrostatic approach along with a static NL dielectric response function of water. The influence of the aqueous solvent microstructure (determined by a strong nonelectrostatic correlation effect between water dipoles within the orientational Debye polarization mode) on electrostatic interactions at the interface was studied in our work. It was shown that the PEI energies can be significantly higher than the energies evaluated by the classical (local) consideration, treating water molecules as belonging to the bulk solvent with a high dielectric constant. Our analysis points to the existence of a rather extended, effective low-dielectric interfacial water shell on the protein surface. The main dielectric properties of this shell (effective thickness together with distance- and orientation-dependent dielectric permittivity function) were evaluated. The dramatic role of this shell was demonstrated when estimating the protein association rate constants.

A comparative study of nano-SiO2 and nano-TiO2 fillers on proton conductivity and dielectric response of a silicotungstic acid-H3PO4-poly(vinyl alcohol) polymer electrolyte.

PubMed

Gao, Han; Lian, Keryn

2014-01-08

The effects of nano-SiO2 and nano-TiO2 fillers on a thin film silicotungstic acid (SiWA)-H3PO4-poly(vinyl alcohol) (PVA) proton conducting polymer electrolyte were studied and compared with respect to their proton conductivity, environmental stability, and dielectric properties, across a temperature range from 243 to 323 K. Three major effects of these fillers have been identified: (a) barrier effect; (b) intrinsic dielectric constant effect; and (c) water retention effect. Dielectric analyses were used to differentiate these effects on polymer electrolyte-enabled capacitors. Capacitor performance was correlated to electrolyte properties through dielectric constant and dielectric loss spectra. Using a single-ion approach, proton density and proton mobility of each polymer electrolyte were derived as a function of temperature. The results allow us to deconvolute the different contributions to proton conductivity in SiWA-H3PO4-PVA-based electrolytes, especially in terms of the effects of fillers on the dynamic equilibrium of free protons and protonated water in the electrolytes.

The effect of in-service aerospace contaminants on X-band dielectric properties of a bismaleimide/quartz composite

NASA Astrophysics Data System (ADS)

Rodriguez, Luis A.; García, Carla; Grace, Landon R.

2015-05-01

The impact of three common aerospace in-service liquid contaminants on the X-band dielectric properties of a polymer composite radar protecting structure (radome) is investigated and quantified. The dielectric properties of the composite laminate are critical to radar transparency, and thus performance, of the radome structure. Further, polymer composites are highly susceptible to absorption of liquids. As such, the effect of common aerospace contaminants on the dielectric properties of composite laminates is crucial. Measurement of relative permittivity and loss tangent via a split-post dielectric resonant technique at 10 GHz is used to determine the effect of water, deicing fluid, and propylene glycol absorption in a three-ply quartz-reinforced bismaleimide laminate. Additionally, fluid uptake kinetics are investigated as a function of liquid type. An approximately linear relationship between fluid content and relative permittivity is observed for all three contaminant types. A 1% increase in contaminant content by weight results in a 7.8%, 4.5%, and 2.5% increase in relative permittivity of the material due to water, deicing fluid, and propylene glycol, respectively. A more significant impact is seen in material loss tangent, where a 1% increase in contaminant content by weight is responsible for a 378.5%, 593.0%, and 441.5% increase in loss tangent due to the aforementioned fluids, respectively. A fluid uptake weight content of 1.31%, 3.41%, and 4.28% is achieved for water, deicing fluid, and propylene glycol respectively, at approximately 1300 hours exposure. Based on the reported observations, the dielectric property degradation of composite laminates due to these commonly used fluids is of significant concern for in-service aircraft radar systems routinely exposed to these contaminants.

Dipolar correlations and the dielectric permittivity of water.

PubMed

Sharma, Manu; Resta, Raffaele; Car, Roberto

2007-06-15

The static dielectric properties of liquid and solid water are investigated within linear response theory in the context of ab initio molecular dynamics. Using maximally localized Wannier functions to treat the macroscopic polarization we formulate a first-principles, parameter-free, generalization of Kirkwood's phenomenological theory. Our calculated static permittivity is in good agreement with experiment. Two effects of the hydrogen bonds, i.e., a significant increase of the average local moment and a local alignment of the molecular dipoles, contribute in almost equal measure to the unusually large dielectric constant of water.

Strain-driven phase transitions and associated dielectric/piezoelectric anomalies in BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Huang, C. W.; Chu, Y. H.; Chen, Z. H.; Wang, Junling; Sritharan, T.; He, Q.; Ramesh, R.; Chen, Lang

2010-10-01

Strain-driven phase transitions and related intrinsic polarization, dielectric, and piezoelectric properties for single-domain films were studied for BiFeO3 using phenomenological Landau-Devonshire theory. A stable and mixed structure between tetragonal and rhombohedral-like (monoclinic) phases is predicted at a compressive misfit strain of um=-0.0382 without an energy barrier. For a tensile misfit strain of um=0.0272, another phase transition between the monoclinic and orthorhombic phases was predicted with sharply high dielectric and piezoelectric responses.

Development of Dielectric Elastomer Nanocomposites as Stretchable and Flexible Actuating Materials

NASA Astrophysics Data System (ADS)

Wang, Yu

Dielectric elastomers (DEs) are a new type of smart materials showing promising functionalities as energy harvesting materials as well as actuating materials for potential applications such as artificial muscles, implanted medical devices, robotics, loud speakers, micro-electro-mechanical systems (MEMS), tunable optics, transducers, sensors, and even generators due to their high electromechanical efficiency, stability, lightweight, low cost, and easy processing. Despite the advantages of DEs, technical challenges must be resolved for wider applications. A high electric field of at least 10-30 V/um is required for the actuation of DEs, which limits the practical applications especially in biomedical fields. We tackle this problem by introducing the multiwalled carbon nanotubes (MWNTs) in DEs to enhance their relative permittivity and to generate their high electromechanical responses with lower applied field level. This work presents the dielectric, mechanical and electromechanical properties of DEs filled with MWNTs. The micromechanics-based finite element models are employed to describe the dielectric, and mechanical behavior of the MWNT-filled DE nanocomposites. A sufficient number of models are computed to reach the acceptable prediction of the dielectric and mechanical responses. In addition, experimental results are analyzed along with simulation results. Finally, laser Doppler vibrometer is utilized to directly detect the enhancement of the actuation strains of DE nanocomposites filled with MWNTs. All the results demonstrate the effective improvement in the electromechanical properties of DE nanocomposites filled with MWNTs under the applied electric fields.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raj, C. Justin, E-mail: cjustinraj@gmail.com; Paramesh, G.; Prakash, B. Shri

Highlights: • Mg doped zinc oxide ceramics were fabricated by co-precipitation/solid state reaction. • MZO ceramics shown a Debye type and colossal dielectric response. • Physical absorption of atmospheric water vapor contributes these high permittivity. • The fabricated ceramic shows Maxwell–Wagner type of relaxation. - Abstract: Zn{sub 1−x}Mg{sub x}O ( ≤ x ≤ 0.1) ceramics were fabricated by conventional solid-state reaction of co-precipitated zinc oxide and magnesium hydroxide nanoparticles. Structural and morphological properties of the fabricated ceramics were studied using X-ray diffraction and scanning electron microscopic analysis. The dielectric measurements of the ceramics were carried out as a function ofmore » frequency and temperature respectively. Interestingly, Mg doped ZnO (MZO) samples exhibited colossal dielectric response (∼1 × 10{sup 4} at 1 kHz) with Debye like relaxation. The detailed dielectric studies and thermal analyses showed that the unusual dielectric response of the samples were originated from the defected grain and grain boundary (GB) conductivity relaxations due to the absorbed atmospheric water vapor (moisture). Impedance spectroscopy was employed to determine the defected grain and GB resistances, capacitances and which supported Maxwell–Wagner type relaxation phenomena.« less

Enhanced dielectric response of GeO{sub 2}-doped CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amaral, F.; School of Technology and Management of Oliveira do Hospital, Oliveira do Hospital, 3400-124 Oliveira; Rubinger, C. P. L.

2009-02-01

CaCu{sub 3}Ti{sub 4}O{sub 12} ceramic samples were prepared by solid state conventional route using stoichiometric amounts of CuO, TiO{sub 2}, and CaCO{sub 3}. Afterward the material was doped with GeO{sub 2} with concentrations up to 6% by weight and sintered at 1050 deg. C for 12 h. The influence of doping on the microstructure, vibrational modes, and dielectric properties of the material was investigated by x-ray diffraction, scanning electron microscopy coupled with an energy dispersive spectrometer, and infrared and dielectric measurements between 100 Hz and 30 MHz. The materials presented huge dielectric response, which increases with doping level relative tomore » undoped CaCu{sub 3}Ti{sub 4}O{sub 12}. The main effect of doping on the microstructure is the segregation of Cu-rich phase in the ceramic grain boundaries. Cole-Cole modeling correlates well the effects of this segregation with the relaxation parameters obtained. The intrinsic phonon contributions for the dielectric response were obtained and discussed together with the structural evolution of the system.« less

Investigation of dielectric behavior of the PVC/BaTiO3 composite in low-frequencies

NASA Astrophysics Data System (ADS)

Berrag, A.; Belkhiat, S.; Madani, L.

2018-04-01

Polyvinyl chloride (PVC) is widely used as insulator in electrical engineering especially as cable insulation sheaths. In order to improve the dielectric properties, polymers are mixed with ceramics. In this paper, PVC composites with different weight percentages 2 wt.%, 5 wt.%, 8 wt.% and 10 wt.% were prepared and investigated. Loss index (𝜀″) and dielectric constant (𝜀‧) have been measured using an impedance analyzer RLC. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) have been used as characterization techniques. The incorporation of BaTiO3 does not modify the crystallinity and the morphology of the PVC but reduces the space charges, therefore the dielectric losses. The frequency response analysis has been followed in the frequency ranges (20-140 Hz and 115-1 MHz). Relaxation frequencies have been evaluated in each frequency range. Experimental measurements have been validated using Cole-Cole’s model. Experimental results show well that BaTiO3 as a filler improves the dielectric properties of PVC.

Effect of fiber content on the thermal conductivity and dielectric constant of hair fiber reinforced epoxy composite

NASA Astrophysics Data System (ADS)

Prasad Nanda, Bishnu; Satapathy, Alok

2018-03-01

This paper reports on the dielectric and thermal properties of hair fibers reinforced epoxy composites. Hair is an important part of human body which also offers protection to the human body. It is also viewed as a biological waste which is responsible for creating environmental pollution due to its low decomposition rate. But at the same time it has unique microstructural, mechanical and thermal properties. In the present work, epoxy composites are made by solution casting method with different proportions of short hair fiber (SHF). Effects of fiber content on the thermal conductivity and dielectric constant of epoxy resin are studied. Thermal conductivities of the composites are obtained using a UnithermTM Model 2022 tester. An HIOKI-3532-50 Hi Tester Elsier Analyzer is used for measuring the capacitance of the epoxy-SHF composite, from which dielectric constant (Dk) of the composite are calculated. A reduction in thermal conductivity of the composite is noticed with the increase in wt. % of fiber. The dielectric constant value of the composites also found to be significantly affected by the fiber content.

The effect of water absorption on the dielectric properties of polyethylene hexagonal boron nitride nanocomposites

NASA Astrophysics Data System (ADS)

Ayoob, Raed; Alhabill, Fuad N.; Andritsch, Thomas; Vaughan, Alun S.

2018-02-01

The effect of water absorption on the dielectric response of polyethylene/hexagonal boron nitride nanocomposites has been studied by dielectric spectroscopy. The nanocomposites have been prepared with hBN concentrations ranging from 2 wt% to 30 wt%. Fourier transform infrared spectroscopy and thermogravimetric analysis revealed a very small amount of hydroxyl groups on the surface of hBN. Mass loss measurements showed that the nanocomposites did not absorb any water under ambient and dry conditions while there was some water absorption under wet conditions. The dielectric spectroscopy results showed a broad relaxation peak, indicative of different states of water with water shells of different thickness, which moved to higher frequencies with increasing water content. However, the dielectric losses were significantly lower than the losses reported in the literature of nanocomposites under wet conditions. In addition, all the absorbed water was successfully removed under vacuum conditions which demonstrated that the interactions between the water and the nanocomposites were very weak, due to the hydrophobic nature of the hBN surface. This is a highly useful property, when considering these materials for applications in electrical insulation.

Order, viscoelastic, and dielectric properties of symmetric and asymmetric alkyl[1]benzothieno[3,2-b][1]benzothiophenes.

PubMed

Grigoriadis, Christos; Niebel, Claude; Ruzié, Christian; Geerts, Yves H; Floudas, George

2014-02-06

The morphology, the viscoelastic, the dielectric properties and the dynamics of phase transformation are studied in symmetrically and asymmetrically substituted alkyl[1]benzothieno[3,2-b][1]benzothiophenes (C8-BTBT) by X-ray scattering, rheology, and dielectric spectroscopy. The interlayer spacing reflects the molecular and supramolecular ordering, respectively, in the symmetrically and asymmetrically substituted BTBTs. In the asymmetric BTBT, the core layer is double in size with a broader network of intermolecular interactions though the increased S-S contacts that is prerequisite for the development of high performance OFET devices. Two crystal states with elastic and viscoelastic responses were identified in the symmetric compound. In contrast, the SmA phase in the asymmetric compound is a viscoelastic solid. A path-dependent dielectric environment with a switchable dielectric permittivity was found in both compounds by cooling below 0 °C with possible implications to charge transport. The kinetics of phase transformation to the crystalline and SmA phases revealed a nucleation and growth mechanism with rates dominated by the low activation barriers.

Fundamentals of dielectric properties measurements and agricultural applications.

PubMed

Nelson, Stuart O

2010-01-01

Dielectrics and dielectric properties are defined generally and dielectric measurement methods and equipment are described for various frequency ranges from audio frequencies through microwave frequencies. These include impedance and admittance bridges, resonant frequency, transmission-line, and free-space methods in the frequency domain and time-domain and broadband techniques. Many references are cited describing methods in detail and giving sources of dielectric properties data. Finally a few applications for such data are presented and sources of tabulated and dielectric properties data bases are identified.

Structural manipulation and tailoring of dielectric properties in SrTi1−xFexTaxO3 perovskites: Design of new lead free relaxors

PubMed Central

Shukla, R.; Patwe, S. J.; Deshpande, S. K.; Achary, S. N.; Krishna, P. S. R.; Shinde, A. B.; Gopalakrishnan, J.; Tyagi, A. K.

2016-01-01

We report composition dependent structure evolution from SrTiO3 to SrFe0.5Ta0.5O3 by powder X-ray and neutron diffraction studies of SrTi1−2xFexTaxO3 (0.00 ≤ × ≤ 0.50) compositions. Structural studies reveal cubic (Pm3m) perovskite-type structure of the parent SrTiO3 for x up to 0.075 and cation disordered orthorhombic (Pbnm) perovskite-type structure for x ≥ 0.33. A biphasic region consisting of a mixture of cubic and orthorhombic structures is found in the range for 0.10 ≤ × ≤ 0.25. Dielectric studies reveal transformation from a normal dielectric to relaxor like properties with increasing Fe3+ and Ta5+ concentration. Dielectric response is maximum at x = 0.33 in the series. The results establish a protocol for designing new lead-free relaxor materials based on the co-substitution of Fe3+ and Ta5+ for Ti4+ in SrTiO3. A complex interplay of strain effects arising from distribution of cations at the octahedral sites of the perovskite structure controls the dielectric properties. PMID:27514668

Interpreting the nonlinear dielectric response of glass-formers in terms of the coupling model

NASA Astrophysics Data System (ADS)

Ngai, K. L.

2015-03-01

Nonlinear dielectric measurements at high electric fields of glass-forming glycerol and propylene carbonate initially were carried out to elucidate the dynamic heterogeneous nature of the structural α-relaxation. Recently, the measurements were extended to sufficiently high frequencies to investigate the nonlinear dielectric response of faster processes including the so-called excess wing (EW), appearing as a second power law at high frequencies in the loss spectra of many glass formers without a resolved secondary relaxation. While a strong increase of dielectric constant and loss is found in the nonlinear dielectric response of the α-relaxation, there is a lack of significant change in the EW. A surprise to the experimentalists finding it, this difference in the nonlinear dielectric properties between the EW and the α-relaxation is explained in the framework of the coupling model by identifying the EW investigated with the nearly constant loss (NCL) of caged molecules, originating from the anharmonicity of the intermolecular potential. The NCL is terminated at longer times (lower frequencies) by the onset of the primitive relaxation, which is followed sequentially by relaxation processes involving increasing number of molecules until the terminal Kohlrausch α-relaxation is reached. These intermediate faster relaxations, combined to form the so-called Johari-Goldstein (JG) β-relaxation, are spatially and dynamically heterogeneous, and hence exhibit nonlinear dielectric effects, as found in glycerol and propylene carbonate, where the JG β-relaxation is not resolved and in D-sorbitol where it is resolved. Like the linear susceptibility, χ1(f), the frequency dispersion of the third-order dielectric susceptibility, χ3(f), was found to depend primarily on the α-relaxation time, and independent of temperature T and pressure P. I show this property of the frequency dispersions of χ1(f) and χ3(f) is the characteristic of the many-body relaxation dynamics of interacting systems which are governed solely by the intermolecular potential, and thermodynamic condition plays no role in this respect. Although linked to χ3(f), dynamic heterogeneity is one of the parallel consequences of the many-body dynamics, and it should not be considered as the principal control parameter for the other dynamic properties of glassforming systems. Results same as χ3(f) at elevated pressures had been obtained before by molecular dynamics simulations from the four-points correlation function and the intermediate scattering function. Naturally all properties obtained from the computer experiment, including dynamics heterogeneity, frequency dispersion, the relation between the α- and JG β-relaxation, and the breakdown of the Stokes-Einstein relation, are parallel consequences of the many-body relaxation dynamics governed by the intermolecular potential.

Giant dielectric response and low dielectric loss in Al{sub 2}O{sub 3} grafted CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajabtabar-Darvishi, A.; Center for Surface and Nanoanalytics; Bayati, R., E-mail: reza.bayati@intel.com, E-mail: mbayati@ncsu.edu, E-mail: wdfei@hit.edu.cn

2015-03-07

This study sheds light on the effect of alumina on dielectric constant and dielectric loss of novel CaCu{sub 3}Ti{sub 4}O{sub 12} composite ceramics. Alumina, at several concentrations, was deposited on the surface of CaCu{sub 3}Ti{sub 4}O{sub 12} particles via sol-gel technique. The dielectric constant significantly increased for all frequencies and the dielectric loss substantially decreased for low and intermediate frequencies. These observations were attributed to the change in characteristics of grains and grain boundaries. It was found that the insulating properties of the grain boundaries are improved following the addition of Al{sub 2}O{sub 3}. The relative density of CaCu{sub 3}Ti{submore » 4}O{sub 12}/Al{sub 2}O{sub 3} composite ceramics decreased compared to the pure CaCu{sub 3}Ti{sub 4}O{sub 12} and the grain size was greatly changed with the alumina content affecting the dielectric properties. With the addition of alumina into CaCu{sub 3}Ti{sub 4}O{sub 12}, tighter interfaces formed. The 6%- and 10%-alumina ceramics showed the minimum dielectric loss and the maximum dielectric constant, respectively. Both the dielectric constant and loss tangent decreased in the 20%-alumina ceramic due to the formation of CuO secondary phase. It was revealed that Al serves as an electron acceptor decreasing the electron concentration, if Al{sup 3+} ions substitute for Ti{sup 4+} ions, and as an electron donor increasing the electron concentration, if Al{sup 3+} ions substitute for Ca{sup 2+} ions. We established a processing-microstructure-properties paradigm which opens new avenues for novel applications of CaCu{sub 3}Ti{sub 4}O{sub 12}/Al{sub 2}O{sub 3} composite ceramics.« less

Structural, dielectric and impedance spectroscopy studies in Co doped La0.7Te0.3MnO3

NASA Astrophysics Data System (ADS)

Uthaman, Bhagya; Revathy, R.; Job, Rojerce Brown; Varma, Manoj Raama

2018-05-01

The effect of cobalt doping on the structural and dielectric properties of the electron-doped manganite La0.7Te0.3Mn1-xCoxO3 (x=0, 0.1, 0.3 and 0.5) has been investigated. Cobalt substitution induces a structural transition from rhombohedral structure (R-3 c space group) to orthorhombic structure (Pbnm space group). It is observed that, dielectric constant decreases with Co concentration which could be due to suppression of double exchange (DE) interaction between Mn2+ and Mn3+. Also, the effect of the grain and grain boundary density on the dielectric response is studied using Cole-Cole plots.

Temperature dependence of electrical properties of mixture of exogenous neurotransmitters dopamine and epinephrine

NASA Astrophysics Data System (ADS)

Patki, Mugdha; Patil, Vidya

2016-05-01

Neurotransmitters are chemical messengers that support the communication between the neurons. In vitro study of exogenous neurotransmitters Dopamine and Epinephrine and their mixture, carried out to learn about their electrical properties being dielectric constant and conductivity amongst others. Dielectric constant and conductivity of the selected neurotransmitters are found to increase with temperature. As a result, the time constant of the system increases with temperature. This change leads to increase in the time taken by the synapse to transport the action potential. The correlation between physical properties of exogenous neurotransmitters and psychological and physiological behaviour of human being may be understood with the help of current study. The response time of Epinephrine is in microseconds whereas response time of Dopamine is in milliseconds. The response time for both the neurotransmitters and their mixture is found to be increasing with temperature indicating the symptoms such as depression, apathy, chronic fatigue and low physical energy with no desire to exercise the body, which are observed during the fever.

Dielectric property measurements in the Electromagnetic Properties Measurement Laboratory

NASA Technical Reports Server (NTRS)

Cravey, Robin L.; Tiemsin, Pacita I.; Bussell, Kerri; Dudley, Kenneth L.

1995-01-01

The capability to measure the dielectric properties of various materials has been developed in the Electromagnetic Properties Measurement Laboratory (EPML) of the Electromagnetics Research Branch (ERB). Two measurement techniques which have been implemented in the EPML to characterize materials are the dielectric probe and waveguide techniques. Several materials, including some for which the dielectric properties are well known, have been measured in an attempt to establish the capabilities of the EPML in determining dielectric properties. Brief descriptions of the two techniques are presented in this report, along with representative results obtained during these measurements.

Light localization and SERS in tip-shaped silicon metasurface.

PubMed

Lagarkov, Andrey; Boginskaya, Irina; Bykov, Igor; Budashov, Igor; Ivanov, Andrey; Kurochkin, Ilya; Ryzhikov, Ilya; Rodionov, Ilya; Sedova, Marina; Zverev, Alexander; Sarychev, Andrey K

2017-07-24

Optical properties of two dimensional periodic system of the silicon micro-cones are investigated. The metasurface, composed of the silicon tips, shows enhancement of the local optical field. Finite element computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric resonances. Various electromagnetic resonances are considered in the dielectric cone. The metal-dielectric resonances, which are excited between metal nanoparticles and dielectric cones, are also considered. The resonance local electric field can be much larger than the field in the usual surface plasmon resonances. To investigate local electric field the signal molecules are deposited on the metal nanoparticles. We demonstrate enhancement of the electromagnetic field and Raman signal from the complex of DTNB acid molecules and gold nanoparticles, which are distributed over the metasurface. The metasurfaces composed from the dielectric resonators can have quasi-continuous spectrum and serve as an efficient SERS substrates.

The dielectric spectroscopy of human red blood cells: the differentiation of old from fresh cells.

PubMed

David, Marcelo; Levy, Evgeniya; Feldman, Yuri; Ben Ishai, Paul; Zelig, Orly; Yedgar, Saul; Barshtein, Gregory

2017-06-22

The objective of the study was to gauge the effect of storage lesions on the dielectric response of red blood cells (RBC), in particular those processes linked to deformations of the cellular membrane known as the β-dispersion. The dielectric response of RBC suspensions, exposed to blood-bank cold storage, was studied using time-domain dielectric spectroscopy (TDDS) in the frequency range of 500 kHz up to 1 GHz. The measured dielectric processes are characterized by their dielectric strength (Δε) and relaxation time (τ). Changes in the dielectric properties of the RBC suspensions due to storage-related lesions were evaluated. For a quantitative characterization of RBC lesions, we measured the deformability of fresh and stored RBC as expressed by their elongation ratio (ER), which was achieved under a shear stress of 3.0 Pa. The results show that the storage of RBC induced a statistically significant decrease of dielectric relaxation times. In addition, a sound correlation between the mean values of ER and the relaxation times was observed (Spearman's correlation coefficient ρ  =  0.847). We draw the conclusion that those alterations in the relaxation time are induced by changes in the shape of the RBC that happen during cold-storage. The evolution of the β-dispersion of RBC opens new possibilities in the blood bank inventory management.

Broadband electromagnetic dipole scattering by coupled multiple nanospheres

NASA Astrophysics Data System (ADS)

Jing, Xufeng; Ye, Qiufeng; Hong, Zhi; Zhu, Dongshuo; Shi, Guohua

2017-11-01

With the development of nanotechnology, the ability to manipulate light at the nanoscale is critical to future optical functional devices. The use of high refractive index dielectric single silicon nanoparticle can achieve electromagnetic dipole resonant properties. Compared with single nanosphere, the use of dimer and trimer introduces an additional dimension (gap size) for improving the performance of dielectric optical devices through the coupling between closely connected silicon nanospheres. When changing the gap size between the nanospheres, the interaction between the particles can be from weak to strong. Compared with single nanospheres, dimerized or trimeric nanospheres exhibit more pronounced broadband scattering properties. In addition, by introducing more complex interaction, the trimericed silicon nanospheres exhibit a more significant increase in bandwidth than expected. In addition, the presence of the substrate will also contribute to the increase in the bandwidth of the nanospheres. The broadband response in dielectric nanostructures can be effectively applied to broadband applications such as dielectric nanoantennas or solar cells.

The contribution of 180° domain wall motion to dielectric properties quantified from in situ X-ray diffraction

DOE PAGES

Fancher, C. M.; Brewer, S.; Chung, C. C.; ...

2016-12-27

Here, the contribution of 180° domain wall motion to polarization and dielectric properties of ferroelectric materials has yet to be determined experimentally. In this paper, an approach for estimating the extent of (180°) domain reversal during application of electric fields is presented. We demonstrate this method by determining the contribution of domain reversal to polarization in soft lead zirconate titanate during application of strong electric fields. At the maximum applied field, domain reversal was determined to account for >80% of the measured macroscopic polarization. We also apply the method to quantify the contribution of domain reversal to the weak-field dielectricmore » permittivity of BaTiO 3. The results of this analysis determined that domain reversal accounts for up to ~70% of the macroscopic dielectric permittivity in BaTiO 3. These results demonstrate the predominance of domain reversal to high and low-field dielectric response in ferroelectric polycrystalline materials.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Yefeng; Gong, Honghong; Xie, Yunchuan

Interface polarization and interface zone have been widely utilized to account for the abnormally improved dielectric properties of composites although their formation is rather vague and their influence has never been directly measured. In this work, micro α-SiC was designed as the filler particles incorporated into poly(vinylidenefluoride-co-chlorotrifluoroethylene) with internal double bonds (P(VDF-CTFE-DB)) to construct polymer micro composites through solution casting method. The dielectric constant of the composites is found to be increasing linearly as SiC content increases at lower content and the highest value is obtained as 83 at 100 Hz, which is unusually higher than both pristine polymer (13@100 Hz) andmore » SiC filler (17@100 Hz). By studying the dielectric properties of a bilayer model composite, the real dielectric permittivity of SiC sheet and P(VDF-CTFE-DB) layer has been directly measured to be significantly enhanced than their original value. The induced polarity between high polar PVDF units in polymer matrix and the electron-hole dipoles in α-SiC is responsible for the elevated dielectric properties of both components, which could address the failure of binary series and parallel models in predicting the dielectric permittivity of 0-3 composites as well. The strong dependence of induced polarity on the volume content, thickness, and polar nature of both components strongly suggests establishing promising high induced polarity between polymer matrix and fillers may provide an alternative strategy for fabricating high-k composites.« less

Hydrothermal process assists undoped and Cr-doped semiconducting ZnO nanorods: Frontier of dielectric property

NASA Astrophysics Data System (ADS)

Debnath, Tanumoy; Saha, Papiya; Patra, Nesla; Das, Sukhen; Sutradhar, Soumyaditya

2018-05-01

The influence of the hydrothermal synthesis route on the grain morphology and thereby the modulation of dielectric response of undoped and Cr3+ ion doped semiconducting ZnO nanoparticles is investigated in this report. The X-ray diffraction study reveals that all the samples are in a polycrystalline single phase of a hexagonal wurtzite structure of ZnO. The field emission scanning electron microscopy study reveals the rod like structure of all the samples. The formation of synthesis route dependent morphology and the morphology dependent physical property of all the samples are the characteristic features of the present work and to date it has not been considered as the specific tool of dielectric property modulation by anyone else. The ultraviolet-visible measurement signifies the superior control over the charge density of the host semiconducting material due to the presence of Cr3+ ions in the structure of ZnO. In the photoluminescence measurement, no significant peak has been observed in the visible region. The frequency and temperature dependent dielectric constants of all the samples were investigated. The consequences of the dielectric measurement suggest that the hydrothermal synthesis route influences the growth mechanism of the semiconducting nanoparticles mostly towards the rod like structure and the doping element influences the charge density, nature of defects, and the defect densities inside the structure of ZnO nanomaterials. All these factors together make the semiconducting ZnO nanomaterials more effective for tailor made applications in magneto-dielectric devices.

Dielectric and modulus analysis of the photoabsorber Cu2SnS3

NASA Astrophysics Data System (ADS)

Lahlali, S.; Essaleh, L.; Belaqziz, M.; Chehouani, H.; Alimoussa, A.; Djessas, K.; Viallet, B.; Gauffier, J. L.; Cayez, S.

2017-12-01

Dielectric properties of the ternary semiconductor compound Cu2SnS3 is studied for the first time in the high temperature range from 300 °C to 440 °C with the frequency range 1 kHz to 1 MHz. The dielectric constant ε ‧ and dielectric loss tan (δ) were observed to increase with temperature and decrease rapidly with frequency to remains constant at high frequencies. The variation of the dielectric loss Ln (ε ") with L n (ω) was found to follow the empirical law, ε " = B ω m (T). The dielectric data were analyzed using complex electrical modulus M* at various temperatures. The activation energy responsible for the relaxation is estimated from the analysis of the modulus spectra. The value of the hopping barrier potential is estimated from the dielectric loss and compared with the value previously obtained from ac-conductivity. These results are critical for understanding the behavior of based polycrystalline family of Cu2SnS3 for absorber materials in solar-cells.

Enhancement of dielectric constant at percolation threshold in CaCu3 Ti4 O12 ceramic fabricated by both solid state and sol-gel process

NASA Astrophysics Data System (ADS)

Mukherjee, Rupam; Garcia, Lucia; Lawes, Gavin; Nadgorny, Boris

2014-03-01

We have investigated the large dielectric enhancement at the percolation threshold by introducing metallic RuO2 grains into a matrix of CaCu3Ti4O12 (CCTO). The intrinsic response of the pure CCTO samples prepared by solid state and sol-gel processes results in a dielectric constant on the order of 104 and 103 respectively with low loss. Scanning electron microscopy and energy dispersive x-ray spectroscopy indicate that a difference in the thickness of the copper oxide enriched grain boundary is the main reason for the different dielectric properties between these two samples. Introducing RuO2 metallic fillers in these CCTO samples yields a sharp increase of the dielectric constant at percolation threshold fc, by a factor of 6 and 3 respectively. The temperature dependence of the dielectric constant shows that the dipolar relaxation plays an important role in enhancing dielectric constant in composite systems.

The enhancement in dielectric and magnetic property in Na and Mn co substituted lanthanum ferrite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rai, Atma, E-mail: atma@iitp.ac.in; Thakur, Awalendra K., E-mail: akt@iitp.ac.in; Centre for Energy and Environment Indian Institute of Technology Patna 800013 India

2016-05-06

Nanocrystalline solid solutions of La{sub 1-x}Na{sub x}Fe{sub 1-y}Mn{sub y}O{sub 3} (x=y=0.00 and 0.25) were prepared via modified Pechini route. No evidence of secondary or impurity phase has been detected up to the detection of error limit of high power X-ray diffractometer. Dielectric property of the samples has been investigated in the frequency range 100 Hz-4MHz at temperature ranging 300–450K. The value of relative permittivity (ε{sub r}) increases drastically and shows colossal dielectric response (∼10{sup 4}) by cosubstitution of Na and Mn as compared to pure LaFeO{sub 3}. Dielectric relaxation peak in loss tangent in both samples have been found and shiftmore » towards higher frequency region as temperature increases. Magnetization-Field (M-H) loop of the calcined sample have been recorded at room temperature (300K) at field ±60kOe. Magnetic property also enhanced by co substitution of Na and Mn. The change in Fe/Mn-O-Fe/Mn angle by co-substitution of Na and Mn in LaFeO{sub 3} and indirect exchange interaction between two different magnetic sub lattices Fe and Mn might be responsible for drastic change. Saturation/maximum magnetic moment increase ∼four times in LNFM25 (5.335emu/g) as compared to pure LaFeO{sub 3} (1.302emu/g).« less

Effects of poling over the orthorhombic-tetragonal phase transition temperature in compositionally homogeneous (K,Na)NbO3-based ceramics

NASA Astrophysics Data System (ADS)

Morozov, M. I.; Kungl, H.; Hoffmann, M. J.

2011-03-01

Li-, Ta-, and Mn-modified (K,Na)NbO3 ceramics with various compositional homogeneity have been prepared by conventional and precursor methods. The homogeneous ceramic has demonstrated a sharper peak in temperature dependent piezoelectric response. The dielectric and piezoelectric properties of the homogeneous ceramics have been characterized at the experimental subcoercive electric fields near the temperature of the orthorhombic-tetragonal phase transition with respect to poling in both phases. Poling in the tetragonal phase is shown to enhance the low-signal dielectric and piezoelectric properties in the orthorhombic phase.

Dielectric properties of vertically aligned multi-walled carbon nanotubes in the terahertz and mid-infrared range

NASA Astrophysics Data System (ADS)

Thomson, Mark D.; Zouaghi, Wissem; Meng, Fanqi; Wiecha, Matthias M.; Rabia, Kaneez; Heinlein, Thorsten; Hussein, Laith; Babu, Deepu; Yadav, Sandeep; Engstler, Jörg; Schneider, Jörg J.; Nicoloso, Norbert; Rychetský, Ivan; Kužel, Petr; Roskos, Hartmut G.

2018-01-01

We investigate the broadband dielectric properties of vertically aligned, multi-wall carbon nanotubes (VACNT), over both the terahertz (THz) and mid-infrared spectral ranges. The nominally undoped, metallic VACNT samples are probed at normal incidence, i.e. the response is predominantly due to polarisation perpendicular to the CNT axis. A detailed comparison of various conductivity models and previously reported results is presented for the non-Drude behaviour we observe in the conventional THz range (up to 2.5 THz). Extension to the mid-infrared range reveals an absorption peak at \

Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys

NASA Astrophysics Data System (ADS)

Baldissera, Gustavo; Persson, Clas

2016-01-01

ZnO1-xYx with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy Eg(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O,Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O,S) is more stable as alloy than Zn(O,Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, ΔEg(0.50) = Eg(ZnO) - Eg(x = 0.50) ≈ 2.2 eV) compared with that of the S-based alloy (ΔEg(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn-anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function ɛ(ω) = ɛ1(ω) + iɛ2(ω) and the absorption coefficient α(ω). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant ɛ∞ is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe₃O₄ nano-fillers: an interface-mediated superior dielectric and EMI shielding performance.

PubMed

Rao, B V Bhaskara; Yadav, Prasad; Aepuru, Radhamanohar; Panda, H S; Ogale, Satishchandra; Kale, S N

2015-07-28

In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm(-3) is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA-SLGAPC-Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz-10 MHz, enhanced by a factor of 4 as compared to that of the PVA-SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell-Wagner-Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2-12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm(-3))(-1), indicating the promising character of this material for flexible EMI shielding applications.

Reversible dielectric property degradation in moisture-contaminated fiber-reinforced laminates

NASA Astrophysics Data System (ADS)

Rodriguez, Luis A.; García, Carla; Fittipaldi, Mauro; Grace, Landon R.

2016-03-01

The potential for recovery of dielectric properties of three water-contaminated fiber-reinforced laminates is investigated using a split-post dielectric resonant technique at X-band (10 GHz). The three material systems investigated are bismaleimide (BMI) reinforced with an eight-harness satin weave quartz fabric, an epoxy resin reinforced with an eight- harness satin weave glass fabric (style 7781), and the same epoxy reinforced with a four-harness woven glass fabric (style 4180). A direct correlation between moisture content, dielectric constant, and loss tangent was observed during moisture absorption by immersion in distilled water at 25 °C for five equivalent samples of each material system. This trend is observed through at least 0.72% water content by weight for all three systems. The absorption of water into the BMI, 7781 epoxy, and 4180 epoxy laminates resulted in a 4.66%, 3.35%, and 4.01% increase in dielectric constant for a 0.679%, 0.608%, and 0.719% increase in water content by weight, respectively. Likewise, a significant increase was noticed in loss tangent for each material. The same water content is responsible for a 228%, 71.4%, and 64.1% increase in loss tangent, respectively. Subsequent to full desorption through drying at elevated temperature, the dielectric constant and loss tangent of each laminate exhibited minimal change from the dry, pre-absorption state. The dielectric constant and loss tangent change after the absorption and desorption cycle, relative to the initial state, was 0.144 % and 2.63% in the BMI, 0.084% and 1.71% in the style 7781 epoxy, and 0.003% and 4.51% in the style 4180 epoxy at near-zero moisture content. The similarity of dielectric constant and loss tangent in samples prior to absorption and after desorption suggests that any chemical or morphological changes induced by the presence of water have not caused irreversible changes in the dielectric properties of the laminates.

A Review: Origins of the Dielectric Properties of Proteins and Potential Development as Bio-Sensors

PubMed Central

Bibi, Fabien; Villain, Maud; Guillaume, Carole; Sorli, Brice; Gontard, Nathalie

2016-01-01

Polymers can be classified as synthetic polymers and natural polymers, and are often characterized by their most typical functions namely their high mechanical resistivity, electrical conductivity and dielectric properties. This bibliography report consists in: (i) Defining the origins of the dielectric properties of natural polymers by reviewing proteins. Despite their complex molecular chains, proteins present several points of interest, particularly, their charge content conferring their electrical and dielectric properties; (ii) Identifying factors influencing the dielectric properties of protein films. The effects of vapors and gases such as water vapor, oxygen, carbon dioxide, ammonia and ethanol on the dielectric properties are put forward; (iii) Finally, potential development of protein films as bio-sensors coated on electronic devices for detection of environmental changes particularly humidity or carbon dioxide content in relation with dielectric properties variations are discussed. As the study of the dielectric properties implies imposing an electric field to the material, it was necessary to evaluate the impact of frequency on the polymers and subsequently on their structure. Characterization techniques, on the one hand dielectric spectroscopy devoted for the determination of the glass transition temperature among others, and on the other hand other techniques such as infra-red spectroscopy for structure characterization as a function of moisture content for instance are also introduced. PMID:27527179

Temperature and Moisture Dependent Dielectric Properties of Legume Flours Associated with Dielectric Heating

USDA-ARS?s Scientific Manuscript database

Dielectric property data are important in developing thermal treatments using radio frequency (RF) and microwave (MW) energy and essential to estimate the heating uniformity in electromagnetic fields. Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean)...

Polarization Coupling in Ferroelectric Multilayers as a Function of Interface Charge Concentration

NASA Astrophysics Data System (ADS)

Okatan, Mahmut; Mantese, Joseph; Alpay, Pamir

2009-03-01

Intriguing properties of multilayered and graded ferroelectrics follow from the electrostatic and electromechanical interactions. The strength of the interlayer coupling depends on the concentration of interfacial defects with short-range local electrostatic fields. Defects may locally relax polarization differences and thus reduce the commensurate bound charge concentration at the interlayer interfaces. In this talk, we develop a theoretical analysis based on non-linear thermodynamics coupled with basic electrostatic relations to understand the role of charge compensation at the interlayer interfaces. The results show multilayered ferroelectrics with systematic variations in the composition may display a colossal dielectric response depending upon the interlayer electrostatic interactions. It is expected that other properties such as the pyroelectric and piezoelectric response will yield concomitant increases through the dielectric permittivity.

Colossal intrinsic magnetoelectric effect in Pb(Fe2/3W1/3)0.83Ti0.17O3

NASA Astrophysics Data System (ADS)

Fraygola, B.; Coelho, Adelino A.; Garcia, D.; Eiras, J. A.

2012-08-01

Dielectric and magnetic properties were investigated in Pb(Fe2/3W1/3)0.83Ti0.17O3 ceramics. The dielectric constant in these samples exhibits colossal changes at the magnetic ordering temperature under the presence of bias external electric fields, which presents a close connection with magnetoelectrics effects (ME), confirming the possibility to control magnetic proprieties with electric fields. The ferroelectromagnetoelastic coefficient was determined from the dielectric response as a function of the electric field. The analysis of magnetic and dielectric susceptibilities based on the Landau-Devonshire thermodynamic formalisms indicates that the ME effects is a contribution of intrinsic ME coupling and a field dependent term.

Measuring changes of radio-frequency dielectric properties of chicken meat during storage

USDA-ARS?s Scientific Manuscript database

Changes in dielectric properties of stored chicken meat were tracked by using a radio-frequency dielectric spectroscopy method. For this purpose, the dielectric properties were measured with an open-ended coaxial-line probe and vector network analyzer over a broad frequency range from 200 MHz to 20...

Enhancement of the electromechanical transduction properties of a silicone elastomer by blending with a conjugated polymer

NASA Astrophysics Data System (ADS)

Carpi, F.; Gallone, G.; Galantini, F.; De Rossi, D.

2008-03-01

The need for high driving electric fields currently limits the diffusion of dielectric elastomer actuation in some areas of potential application, especially in the case of biomedical disciplines. A reduction of the driving fields may be achieved with new elastomers offering intrinsically superior electromechanical properties. So far, most of attempts in this direction have been focused on composites between elastomer matrixes and high-permittivity ceramic fillers, yielding to limited results. In this work, the electromechanical response of a silicone rubber (poly-dimethyl-siloxane) was improved by blending, rather than loading, the elastomer with a highly polarizable conjugated polymer (undoped poly-hexyl-thiophene). Very low percentages (1-6 wt%) of poly-hexyl-thiophene yielded both an increase of the dielectric permittivity and an unexpected reduction of the tensile elastic modulus. Both these factors contributed to a remarkable increase of the electromechanical response, which reached a maximum at 1 wt% content of conjugated polymer. This approach may lead to the development of new types of improved dielectric elastomers for actuation.

Analysis of transmittance properties in 1D hybrid dielectric photonic crystal containing superconducting thin films

NASA Astrophysics Data System (ADS)

Soltani, Osswa; Zaghdoudi, Jihene; Kanzari, Mounir

2018-06-01

By means of two fluid model and transfer matrix method (TMM), we investigate theoretically the transmittance properties of a defective hybrid dielectric-dielectric photonic crystal that contains a superconducting material as a defect layer. The considered hybrid photonic structure is: H(LH) 7(HLSLH) P H(LH) 7 , where H is the high refractive index dielectric, L is the low refractive index dielectric, S is the superconducting material and P is the repetitive number. The results show that the variation of the number and the positions of the transmissions modes depend strongly on the repetitive number P, the temperature T and the thickness of the layer S. An improvement of the spectral response is obtained with the exponential gradation of layer thicknesses dj =d0 + βejα , where d0 is the initial thickness of the layer j, α and β are two particular constants for each material. In addition, the effect of the incident angle for both transverse electric (TE) and transverse magnetic (TM) polarizations on the transmittance spectrum is discussed. As a result, we propose a tunable narrow stop-band polychromatic filter that covers the visible wavelength.

Equivalent circuit modeling of the dielectric properties of rubber wood at low frequency

Treesearch

Wan M. Daud; Kaida B. Khalid; Aziz H.A. Sidek

2000-01-01

Dielectric properties of rubber wood were studied at various moisture contents and grain directions at low frequencies from 10-2 to 105 Hz. Results showed that the moisture content of wood affected the dielectric properties considerably. Dielectric data at different anisotropic directions, i.e., longitudinal, radial, and...

Analysis of the dielectric properties of trunk wood in dominant conifer species from New England and Siberia

NASA Technical Reports Server (NTRS)

Ranson, K. J.; Rock, B. N.; Salas, W. A.; Smith, K.; Williams, D. L.

1992-01-01

Data were collected for dominant conifer species. Dielectric properties of trunk wood were measured using a C-band dielectric probe. For certain specimens, electrical resistance was also measured using a shigometer. The water status of the trees studies was determined either by use of a Scholander pressure chamber on branch samples collected simultaneously with dielectric measurements or by fresh-weight/dry-weight assessment of wood core samples extracted and analyzed with the dielectric probe and shigometer. Diurnal delectric properties and xylem water column tension are inversely correlated such that real and imaginary dielectric values drop as tension increases. The dielectric properties were positively correlated with wood core moisture content while electrical resistance was poorly correlated with wood core moisture content in one species studied. Results support the view that dielectric properties are strongly correlated with moisture status in trunk wood, and possibly ion concentrations associated with decay processes in damaged specimens.

A large-scale measurement of dielectric properties of normal and malignant colorectal tissues obtained from cancer surgeries at Larmor frequencies.

PubMed

Li, Zhou; Deng, Guanhua; Li, Zhe; Xin, Sherman Xuegang; Duan, Song; Lan, Maoying; Zhang, Sa; Gao, Yixin; He, Jun; Zhang, Songtao; Tang, Hongming; Wang, Weiwei; Han, Shuai; Yang, Qing X; Zhuang, Ling; Hu, Jiani; Liu, Feng

2016-11-01

Knowledge of dielectric properties of malignant human tissues is necessary for the recently developed magnetic resonance (MR) technique called MR electrical property tomography. This technique may be used in early tumor detection based on the obvious differentiation of the dielectric properties between normal and malignant tissues. However, the dielectric properties of malignant human tissues in the scale of the Larmor frequencies are not completely available in the literature. In this study, the authors focused only on the dielectric properties of colorectal tumor tissue. The dielectric properties of 504 colorectal malignant samples excised from 85 patients in the scale of the Larmor frequencies were measured using the precision open-ended coaxial probe method. The obtained complex-permittivity data were fitted to the single-pole Cole-Cole model. The median permittivity and conductivity for the malignant tissue sample were 79.3 and 0.881 S/m at 128 MHz, which were 14.6% and 17.0% higher, respectively, than those of normal tissue samples. Significant differences between normal and malignant tissues were found for the dielectric properties (p < 0.05). Experimental results indicated that the dielectric properties were significantly different between normal and malignant tissues for colorectal tissue. This large-scale clinical measurement provides more subtle base data to validate the technique of MR electrical property tomography.

The effect of dopants on the microwave dielectric properties of Ba(Mg{sub 0.33}Ta{sub 0.67})O{sub 3} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Surendran, Kuzhichalil P.; Sebastian, Mailadil T.; Mohanan, Pezholil

2005-11-01

The effect of dopants with different valencies and ionic radii on the densification, structural ordering, and microwave dielectric properties of Ba(Mg{sub 1/3}Ta{sub 2/3})O{sub 3} (BMT) is investigated. It is found that dopants such as Sb{sub 2}O{sub 5}, MnO, ZrO{sub 2}, WO{sub 3}, and ZnO improve the microwave dielectric properties of BMT. Addition of trivalent dopants is detrimental to the cation ordering and dielectric properties of BMT. A correlation between the microwave dielectric properties of BMT and ionic radii of the dopant has been established. The variation of the dielectric properties of pure and doped BMT at cryogenic temperatures is alsomore » discussed.« less

Design and characterization of dielectric subwavelength focusing lens with polarization dependence

NASA Astrophysics Data System (ADS)

Kim, Sung W.; Pang, Lin; Fainman, Yeshaiahu

2016-03-01

We introduce and develop design, fabrication and characterization methodology for engineering the effective refractive index of a composite dielectric planar surface created by controlling the density of deeply subwavelength low index nanoholes (e.g., air) in a high index dielectric layer (e.g., Si). The nanoscale properties of a composite dielectric layer allows for full control of the optical wavefront phase by designing arbitrary space-variant refractive index profiles. We present the composite dielectric metasurface microlens exploiting symmetric design to achieve polarization invariant impulse response, and use asymmetric design to demonstrate polarization sensitive impulse response of the lens. This composite dielectric layers lenses were fabricated by patterning nanohole distributions on a dielectric surface and etching to submicron depths. Our dielectric microlens with asymmetric distribution of neff (neff x ≠ neff y) demonstrates a graded index lens with polarization dependent focusing with of 32um and 22 um for linearly x- and y-polarized light, respectively operating at a wavelength of λ = 1550nm. We also show numerically and demonstrate experimentally achromatic performance of the devices operating in the wavelength range of 1500nm - 1900nm with FWHM of the focal spots of about 4um. Namely, we have constructed a graded index lens that can overcome diffraction effects even when aperture/wavelength (D/λ) is smaller than 40. The demonstrated novel approach to engineer dielectric composite nanosurfaces has the potential to realize arbitrary phase functions with minimal insertion loss, submicron thickness and miniaturization to reduce element size and weight, and may have a significant impact on numerous miniature imaging systems applications.

Elastic properties of spherically anisotropic piezoelectric composites

NASA Astrophysics Data System (ADS)

Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming

2010-09-01

Effective elastic properties of spherically anisotropic piezoelectric composites, whose spherically anisotropic piezoelectric inclusions are embedded in an infinite non-piezoelectric matrix, are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials under a uniform external strain are derived exactly. Taking into account of the coupling effects of elasticity, permittivity and piezoelectricity, the formula is derived for estimating the effective elastic properties based on the average field theory in the dilute limit. An elastic response mechanism is revealed, in which the effective elastic properties increase as inclusion piezoelectric properties increase and inclusion dielectric properties decrease. Moreover, a piezoelectric response mechanism, of which the effective piezoelectric response vanishes due to the symmetry of spherically anisotropic composite, is also disclosed.

Structure and dielectric properties of Na0.5Bi0.5TiO3-CaTiO3 solid solutions

NASA Astrophysics Data System (ADS)

Birks, E.; Dunce, M.; Ignatans, R.; Kuzmin, A.; Plaude, A.; Antonova, M.; Kundzins, K.; Sternberg, A.

2016-02-01

Despite wide studies of Na0.5Bi0.5TiO3, structure of this material and its connection with the observed physical properties still raise numerous questions due to mutually contradicting results obtained. Here, structure and dielectric properties of poled and unpoled Na0.5Bi0.5TiO3-CaTiO3 solid solutions are studied, projecting the obtained concentration dependence of structure and dielectric properties on pure Na0.5Bi0.5TiO3 as the end member of this material group. X-ray diffraction patterns for Na0.5Bi0.5TiO3-CaTiO3 solid solutions reveal dominating of an orthorhombic Pnma phase, even for the compositions approaching the end composition (Na0.5Bi0.5TiO3), whereas structure of pure Na0.5Bi0.5TiO3 can be considered, assuming coexistence of rhombohedral and orthorhombic phases. This allows one to avoid appearance of a large difference of rhombohedral distortions between the unpoled and poled Na0.5Bi0.5TiO3, if the rhombohedral distortion is calculated as for single R3c phase. Features of dielectric permittivity, corresponding to the observed structural phase transition, are identified. It is discussed that the rhombohedral R3c phase is responsible for appearance of the frequency-dependent shoulder of dielectric permittivity temperature dependence, characteristic for unpoled Na0.5Bi0.5TiO3.

Epoxy matrix with triaromatic mesogenic unit in dielectric spectroscopy observation

NASA Astrophysics Data System (ADS)

Włodarska, Magdalena; Mossety-Leszczak, Beata; Bąk, Grzegorz W.; Kisiel, Maciej; Dłużniewski, Maciej; Okrasa, Lidia

2018-04-01

This paper describes the dielectric response of a selected liquid crystal epoxy monomer (plain and in curing systems) in a wide range of frequency and temperature. The dielectric spectroscopy, thanks to its sensitivity, is a very good tool for studying phase transitions, reaction progress, or material properties. This sensitivity is important in the case of liquid crystal epoxy resins, where properties of the final network depend on the choice of monomers, curing agents, curing conditions and post-curing treatment, or applying an external electric or magnetic field during the reaction. In most of the obtained cured products, the collected dielectric data show two relaxation processes. The α-process is related to a structural reorientation; it can usually be linked with the glass transition and the mechanical properties of the material. The β-process can be identified as a molecular motion process, probably associated with the carboxyl groups in the mesogen. A transient Maxwell-Wagner relaxation observed in one of the compositions after the initial curing is removed by post-curing treatment at elevated temperatures. Post-curing is therefore necessary for obtaining uniformly cured products in those cases. In the investigated systems, the choice of a curing agent can change the glass transition temperature by at least 70 °C. The obtained results are in a good agreement with an earlier study employing other techniques. Finally, we assess the influence of the direction of mesogen alignment on the dielectric properties of one selected system, where a global order was induced by applying an external magnetic field in the course of curing.

Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films.

PubMed

Kang, Seung Beom; Kwak, Min Hwan; Choi, Muhan; Kim, Sungil; Kim, Taeyong; Cha, Eun Jong; Kang, Kwang Yong

2011-11-01

Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.

Agricultural wastes as a resource of raw materials for developing low-dielectric glass-ceramics

PubMed Central

Danewalia, Satwinder Singh; Sharma, Gaurav; Thakur, Samita; Singh, K.

2016-01-01

Agricultural waste ashes are used as resource materials to synthesize new glass and glass-ceramics. The as-prepared materials are characterized using various techniques for their structural and dielectric properties to check their suitability in microelectronic applications. Sugarcane leaves ash exhibits higher content of alkali metal oxides than rice husk ash, which reduces the melting point of the components due to eutectic reactions. The addition of sugarcane leaves ash in rice husk ash promotes the glass formation. Additionally, it prevents the cristobalite phase formation. These materials are inherently porous, which is responsible for low dielectric permittivity i.e. 9 to 40. The presence of less ordered augite phase enhances the dielectric permittivity as compared to cristobalite and tridymite phases. The present glass-ceramics exhibit lower losses than similar materials synthesized using conventional minerals. The dielectric permittivity is independent to a wide range of temperature and frequency. The glass-ceramics developed with adequately devitrified phases can be used in microelectronic devices and other dielectric applications. PMID:27087123

Spin correlated dielectric memory and rejuvenation in multiferroic CuCrS{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karmakar, A.; Dey, K.; Majumdar, S.

We report a rare consequence of memory effect in dielectric response (ϵ) and magnetic field induced rejuvenation in a relaxor-type multiferroic chalcogenide, CuCrS{sub 2}. Despite reasonably high conductivity, we are able to detect significant spontaneous polarization using an improvised technique verifying ferroelectric (FE) order. Concomitant appearance of both FE and antiferromagnetic orders authenticates multiferroicity. A smeared out FE transition and strong frequency dependence of the broadened peak in ϵ obeying Dynamical scaling law signify relaxor properties. We discuss the role of geometrical frustration in the antiferromagnetically coupled layered triangular lattice and metal ligand hybridization for these unusual properties.

Dielectric dispersion in pure and doped lithium rubidium sulphate

NASA Astrophysics Data System (ADS)

Kassem, M. E.; El-Muraikhi, M.; Al-Houty, L.; Mohamed, A. A.

The frequency (102 - 105 Hz) dependence of the dielectric properties of lithium rubidium sulphate (LRS) are reported in the vicinity of the transition temperature Tc = 477 K. The a.c. conductivity σ(ω) shows a strong temperature dependence and weak frequency response. The dielectric constant in this region shows a strong frequency dispersion. A Cole-Cole diagram was used to determine the distribution parameter and the molecular relaxation time. The effect of doping with Dy+3, Sm+3 and V+3, was also studied. It was found that doping gives rise to localized states which produce a disorder in the structure of LiRbSO4.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bissa, Shivangi; Naruka, Preeti; Bishnoi, Nidhi

In the present study the dielectric optical response of various nanostructures of ZnO deposited on silica substrate has been studied using Maxwell-Garnett Effective Medium Theory. Using the volume filling factors for different nanostructures of ZnO the effective dielectric constant has been evaluated. The variation of this effective dielectric constant with the frequency of applied signal has been investigated. Moreover, the reflectance of the film, power absorption and variation of refractive index with frequency has been studied. The results obtained show that the quantum confinement effects in ZnO nano-structural films deposited on silica substrate give rise to distinct optical properties makingmore » it an ideal choice for high power THz generation.« less

Dipolar ordering and glassy freezing in methanol-{beta}-hydroquinone-clathrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woll, H.; Rheinstadter, M. C.; Kruchten, F.

2001-06-01

The dielectric, structural, and thermodynamic properties of single crystals of methanol-{beta}-hydroquinone-clathrates have been studied as function of temperature and of the concentration x of the polar guest molecules. At higher temperatures the dielectric response along the threefold crystal axis is of the quasi-one-dimensional Ising type. At lower temperatures the higher concentrated samples order antiferroelectrically whereas the lower concentrated ones freeze into dipole glasses. The behavior is interpreted in terms of the methanol dipole moments coupled by the electric dipole-dipole interaction which is highly frustrated because of the rhombohedral symmetry of the lattice. The dielectric relaxations have been analyzed.

Space charge effects on the dielectric response of polymer nanocomposites

NASA Astrophysics Data System (ADS)

Shen, Zhong-Hui; Wang, Jian-Jun; Zhang, Xin; Lin, Yuanhua; Nan, Ce-Wen; Chen, Long-Qing; Shen, Yang

2017-08-01

Adding high-κ ceramic nanoparticles into polymers is a general strategy to improve the performances in energy storage. Classic effective medium theories may fail to predict the effective permittivity in polymer nanocomposites wherein the space charge effects are important. In this work, a computational model is developed to understand the space charge effects on the frequency-dependent dielectric properties including the real permittivity and the loss for polymer nanocomposites with both randomly distributed and aggregated nanoparticle fillers. It is found that the real permittivity of the SrTiO3/polyethylene (12% SrTiO3 in volume fraction) nanocomposite can be increased to as high as 60 when there is nanoparticle aggregation and the ion concentration in the bulk polymer is around 1016 cm-3. This model can be employed to quantitatively predict the frequency-dependent dielectric properties for polymer nanocomposites with arbitrary microstructures.

Research of microwave scattering properties of snow fields

NASA Technical Reports Server (NTRS)

Angelakos, D. J.

1978-01-01

The results obtained in the research program of microwave scattering properties of snow fields are presented. Experimental results are presented showing backscatter dependence on frequency (5.8-8.0 GHz), angle of incidence (0-60 degrees), snow wetness (time of day), and frequency modulation (0-500 MHz). Theoretical studies are being made of the inverse scattering problem yielding some preliminary results concerning the determination of the dielectric constant of the snow layer. The experimental results lead to the following conclusions: snow layering affects backscatter, layer response is significant up to 45 degrees of incidence, wetness modifies snow layer effects, frequency modulation masks the layer response, and for the proper choice of probing frequency and for nominal snow depths, it appears to be possible to measure the effective dielectric constant and the corresponding water content of a snow pack.

Electromechanical response of silk fibroin hydrogel and conductive polycarbazole/silk fibroin hydrogel composites as actuator material.

PubMed

Srisawasdi, Thanida; Petcharoen, Karat; Sirivat, Anuvat; Jamieson, Alexander M

2015-11-01

Pure silk fibroin (SF) hydrogel and polycarbazole/silk fibroin (SF/PCZ) hydrogels were fabricated by solvent casting technique to evaluate electromechanical responses, dielectric properties, and cantilever deflection properties as functions of electric field strength, SF concentration, glutaraldehyde concentration, and PCZ concentration in the blends. Electromechanical properties were characterized in oscillatory shear mode at electric field strengths ranging from 0 to 600V/mm and at a temperature of 27°C. For both the pristine SF and SF/PCZ hydrogels, the storage modulus response (ΔG') and the storage modulus sensitivity (ΔG'/G'0) increased dramatically with increasing electric field strength. The pristine hydrogel possessed the highest storage modulus sensitivity value of 5.87, a relatively high value when compared with other previously studied electroactive polymers. With the addition of conductive PCZ in SF hydrogel, the storage modulus sensitivity and the relative dielectric constant decreased; the conductive polymer thus provided the softening effect under electric field. In the deflection response, the dielectrophoresis force and deflection distance increased monotonically with electric field strength, where the pure SF hydrogel showed the highest deflection distance and dielectrophoresis force. Copyright © 2015 Elsevier B.V. All rights reserved.

Effects of dopant induced defects on structural, multiferroic and optical properties of Bi1-x Pb x FeO3 (0 ≤ x ≤ 0.3) ceramics

NASA Astrophysics Data System (ADS)

Hassnain Jaffari, G.; Aftab, M.; Samad, Abdus; Mumtaz, Fiza; Awan, M. S.; Shah, S. Ismat

2018-01-01

Bi1-x Pb x FeO3 (0 ≤ x ≤ 0.3) has been characterized in detail with an aim to identify role of defect such as dopant, various vacancies, grain boundaries etc, and their effect on structural, optical and multiferroic properties. Structural analysis revealed that Pb substitution transforms the rhombohedral phase of BiFeO3 to the pseudocubic phase for x ≥ 0.15, consistently all vibrational Raman modes associated with the rhombohedral phase are found disappeared. Optical response revealed weakening of the d-d transitions with Pb addition indicating change in the Fe atoms environment consistent with the transition from non-centrosymmetric to the centrosymmetric structure. Transport and dielectric responses are explained in terms of hopping due to the presence of defects like oxygen vacancies and grain boundary conduction. In the high temperature regime, grain boundary conduction led to decrease in resistivity with the presence of a hump that is associated with hopping conduction. Extrinsic contributions in the transport properties correlate well with dielectric response. Magnetic and ferroelectric responses are also presented where role of oxygen vacancies defects has been clearly identified.

Measurement of the dielectric properties of sawdust between 0.5 and 15 GHz

USDA-ARS?s Scientific Manuscript database

Rapid, nondestructive, and subsurface sensing of material properties such as water content can be achieved through dielectric measurements. The interaction between the electromagnetic waves and the material is defined by the dielectric properties, which can be used to determine the physical properti...

Influence of anisotropic strain on the dielectric and ferroelectric properties of SrTiO3 thin films on DyScO3 substrates

NASA Astrophysics Data System (ADS)

Biegalski, M. D.; Vlahos, E.; Sheng, G.; Li, Y. L.; Bernhagen, M.; Reiche, P.; Uecker, R.; Streiffer, S. K.; Chen, L. Q.; Gopalan, V.; Schlom, D. G.; Trolier-McKinstry, S.

2009-06-01

The in-plane dielectric and ferroelectric properties of coherent anisotropically strained SrTiO3 thin films grown on orthorhombic (101) DyScO3 substrates were examined as a function of the angle between the applied electric field and the principal directions of the substrate. The dielectric permittivity revealed two distinct maxima as a function of temperature along the [100]p and [010]p SrTiO3 pseudocubic directions. These data, in conjunction with optical second-harmonic generation, show that the switchable ferroelectric polarization develops first predominantly along the in-plane axis with the larger tensile strain before developing a polarization component along the perpendicular direction with smaller strain as well, leading to domain twinning at the lower temperature. Finally, weak signatures in the dielectric and second-harmonic generation response were detected at the SrTiO3 tilt transition close to 165 K. These studies indicate that anisotropic biaxial strain can lead to new ferroelectric domain reorientation transitions that are not observed in isotropically strained films.

Effect of cobalt doping on structural and dielectric properties of nanocrystalline LaCrO3

NASA Astrophysics Data System (ADS)

Zarrin, Naima; Husain, Shahid

2018-05-01

Pure and Co doped Lanthanum chromite (LaCrO3) nanoparticles, LaCr1-xCoxO3 (0≤x≤0.3), have been synthesized through sol-gel process and their structural, morphological and dielectric properties have been studied. X ray diffraction patterns reveal that the samples are in single phase having orthorhombic structure with Pnma space group. Structural parameters are refined by Rietveld refinement using Fullprof software. Lattice parameters and unit cell volume are found to decrease with increase in Co doping. Crystallite size is calculated using Scherrer equation and is also found to decrease with increase in Co concentration. Surface morphology is examined using SEM-EDX analysis, which confirms the formation of regular and homogeneous samples without any impurities. The value of dielectric constant (ɛ') decreases with the increase in frequency while it enhances with the increase in Co concentration. The log (ɛ'×f) versus log (f) graphs have been plotted to verify the universal dielectric response (UDR) model. All the samples follow UDR model in the low frequency range.

Dielectric characteristics of Mn-doped LaTiO3+δ ceramics

NASA Astrophysics Data System (ADS)

Chen, Yan; Cui, Yimin

A series of ceramic composites of Mn-doped La1- x MnxTiO3+ δ and LaMnxTi1- x O3+ δ (x = 0.1, 0.2) were synthesized by conventional solid-state reaction method. The low-frequency complex dielectric properties of the composites were investigated as functions of temperature (77 K <= T <= 360 K) and frequency (100 Hz <= f <= 1 MHz), respectively. The dielectric constant of A-site doped samples is higher than that of B-site doped samples. The loss tangent of low doped samples is much less than that of high doped samples. The A-site doped composites exhibit intrinsic dielectric response with a dielectric constant of 40 in the temperature below 250 K. Interestingly, the dielectric constants of B-site doped ceramics increase slightly in the temperature range from 77 to 360 K. And it is clearly observed that extraordinarily high dielectric loss tangent ( 6) appear at low frequency (100 Hz) in LaMn0.2Ti0.8O3+ δ , which is 8 times larger than that of LaMn0.1Ti0.9O3+ δ , which indicates that the doped content can affect the intrinsic dielectric characteristics significantly.

Classical density-functional theory of inhomogeneous water including explicit molecular structure and nonlinear dielectric response.

PubMed

Lischner, Johannes; Arias, T A

2010-02-11

We present an accurate free-energy functional for liquid water written in terms of a set of effective potential fields in which fictitious noninteracting water molecules move. The functional contains an exact expression of the entropy of noninteracting molecules and thus provides an ideal starting point for the inclusion of complex intermolecular interactions which depend on the orientation of the interacting molecules. We show how an excess free-energy functional can be constructed to reproduce the following properties of water: the dielectric response; the experimental site-site correlation functions; the surface tension; the bulk modulus of the liquid and the variation of this modulus with pressure; the density of the liquid and the vapor phase; and liquid-vapor coexistence. As a demonstration, we present results for the application of this theory to the behavior of liquid water in a parallel plate capacitor. In particular, we make predictions for the dielectric response of water in the nonlinear regime, finding excellent agreement with known data.

Molecular polarizability of water from local dielectric response theory

DOE PAGES

Ge, Xiaochuan; Lu, Deyu

2017-08-08

Here, we propose a fully ab initio theory to compute the electron density response under the perturbation in the local field. This method is based on our recently developed local dielectric response theory [Phys. Rev. B 92, 241107(R), 2015], which provides a rigorous theoretical framework to treat local electronic excitations in both nite and extended systems beyond the commonly employed dipole approximation. We have applied this method to study the electronic part of the molecular polarizability of water in ice Ih and liquid water. Our results reveal that the crystal field of the hydrogen-bond network has strong anisotropic effects, whichmore » significantly enhance the out-of-plane component and suppress the in-plane component perpendicular to the bisector direction. The contribution from the charge transfer is equally important, which increases the isotropic molecular polarizability by 5-6%. Our study provides new insights into the dielectric properties of water, which form the basis to understand electronic excitations in water and to develop accurate polarizable force fields of water.« less

A large-scale study of the ultrawideband microwave dielectric properties of normal, benign and malignant breast tissues obtained from cancer surgeries

NASA Astrophysics Data System (ADS)

Lazebnik, Mariya; Popovic, Dijana; McCartney, Leah; Watkins, Cynthia B.; Lindstrom, Mary J.; Harter, Josephine; Sewall, Sarah; Ogilvie, Travis; Magliocco, Anthony; Breslin, Tara M.; Temple, Walley; Mew, Daphne; Booske, John H.; Okoniewski, Michal; Hagness, Susan C.

2007-10-01

The development of microwave breast cancer detection and treatment techniques has been driven by reports of substantial contrast in the dielectric properties of malignant and normal breast tissues. However, definitive knowledge of the dielectric properties of normal and diseased breast tissues at microwave frequencies has been limited by gaps and discrepancies across previously published studies. To address these issues, we conducted a large-scale study to experimentally determine the ultrawideband microwave dielectric properties of a variety of normal, malignant and benign breast tissues, measured from 0.5 to 20 GHz using a precision open-ended coaxial probe. Previously, we reported the dielectric properties of normal breast tissue samples obtained from reduction surgeries. Here, we report the dielectric properties of normal (adipose, glandular and fibroconnective), malignant (invasive and non-invasive ductal and lobular carcinomas) and benign (fibroadenomas and cysts) breast tissue samples obtained from cancer surgeries. We fit a one-pole Cole-Cole model to the complex permittivity data set of each characterized sample. Our analyses show that the contrast in the microwave-frequency dielectric properties between malignant and normal adipose-dominated tissues in the breast is considerable, as large as 10:1, while the contrast in the microwave-frequency dielectric properties between malignant and normal glandular/fibroconnective tissues in the breast is no more than about 10%.

Use of material dielectric properties in agricultural applications

USDA-ARS?s Scientific Manuscript database

The use of dielectric properties of materials for applications in agriculture are reviewed, and research findings on use of dielectric heating of materials and on sensing of product moisture content and other quality factors are discussed. Dielectric heating applications, include treatment of seed...

Dielectric properties of agricultural materials and their application

USDA-ARS?s Scientific Manuscript database

This book is prepared as a comprehensive source of information on dielectric properties of agricultural materials for scientific researchers and engineers involved in practical application of radio-frequency and microwave energy for potential problem solutions. Dielectric properties of materials det...

Calcination temperature effect on the microstructure and dielectric properties of M-type strontium hexagonal ferrites

NASA Astrophysics Data System (ADS)

Mohammed, J.; Sharma, Jyoti; Kumar, Sachin; Trudel, T. T. Carol; Srivastava, A. K.

2017-07-01

M-type hexagonal ferrites have found wide application in electronics industry due to the possibility of tuning properties such as dielectric properties. An improved dielectric property is useful in high frequency application. In this paper, we studied the effect of calcination temperature on structural and dielectric properties of Al-Mn substituted M-type strontium hexagonal ferrites with chemical composition Sr1-xAlxFe12-yMnyO19 (x=0.3 and y=0.6) synthesized by sol-gel auto-combustion method. The prepared sample was sintered at four different temperatures (T=750°C, 850°C, 950°C and 1050°C) for 5 hours. Characterisations of the synthesized samples were carried out using X-ray diffraction (XRD), impedance analyser, field emission electron microscope (FE-SEM) and energy dispersive X-ray (EDX) spectroscopy. The dielectric properties were explained on the basis of Koop's phenomenological theory and Maxwell Wagner theory. The sample calcinated at 750°C shows the highest value of dielectric constant and AC conductivity whereas that calcinated at 1050°C exhibit the lowest dielectric losses.

Colossal Permittivity in Advanced Functional Heterogeneous Materials: The Relevance of the Local Measurements at Submicron Scale

NASA Astrophysics Data System (ADS)

Fiorenza, Patrick; Nigro, Raffaella Lo; Raineri, Vito

Recently, giant dielectric permittivities (ɛ ' ˜ 104) have been found in several nonferroelectric materials such as CaCu3Ti4O12 (CCTO) (Subramanian et al., J. Solid State Chem. 151:323, 2000; Homes et al., Science 293:673, 2001), doped-NiO (Wu et al., Phys. Rev. Lett. 89:217601, 2002) systems (Li x Ti y Ni1 - x - y O, Li x Si y Ni1 - x - y O, Ki x Ti y Ni1 - x - y O), CuO, (Lin et al., Phys. Rev. B 72:014103, 2005; Sarkar et al., App. Phys. Lett. 92:142901, 2008) etc., and most important, the high ɛ ' values of these materials are almost independent over a wide range of temperature. This is one of the most intriguing features for their implementations in microelectronics devices, and as a consequence, these materials have been subjected to extensive research. Here, an introduction to such materials and to the methods for their dielectric characterization is given. So far, the crucial question is whether the large dielectric response is an intrinsic property of new class of crystals or an extrinsic property originated by a combination of the structural properties and other features such as defects and inhomogeneities. Preliminary, this peculiar dielectric behavior has been explained in powder ceramics by the internal barrier layer capacitor (IBLC) model, that is the presence of semiconducting domains surrounded by thin insulating regions within the crystal microstructure. It has been considered the most appropriate model and it has been generally accepted to explain the giant response of these materials. However, it could not be transferred to single crystals and thin films. In this scenario, scanning probe-based methods (like STM, KPFM, C-AFM, SIM etc) represent the most powerful instrument to understand the colossal permittivity-related physical phenomena, by investigations at nanoscale, clarifying the local effects responsible of the rising of macroscopic giant dielectric responses. Scanning probe microscopy investigations showed the relevance of inhomogeneity within single crystal, polycrystalline ceramics, and thin films. In particular, they are powerful tools to point out the presence of few nanometer wide internal barrier layers and of electrical domains, which are not recognisable with standard macroscopic electric characterization techniques.

Structural and dielectric properties of CTAB modified ZrO2 nanoparticles

NASA Astrophysics Data System (ADS)

Sidhu, Gaganpreet Kaur; Tripathi, S. K.; Kumar, Rajesh

2016-05-01

Zirconia (ZrO2) has been considered as one of the most investigated materials among various metal oxides due its outstanding dielectric properties and ionic conduction properties, which is mainly due to its high oxygen ion conduction. ZrO2 nanoparticles were synthesized using surfactant (CTAB) to study the variation of its dielectric behavior at room temperature. Surfactants form a unique class of chemical compounds, because of their remarkable ability to influence the properties of surfaces and interfaces of nanostructures. The dielectric properties of prepared nanoparticles were studied using LCR meter.

Stress effects in ferroelectric perovskite thin-films

NASA Astrophysics Data System (ADS)

Zednik, Ricardo Johann

The exciting class of ferroelectric materials presents the engineer with an array of unique properties that offer promise in a variety of applications; these applications include infra-red detectors ("night-vision imaging", pyroelectricity), micro-electro-mechanical-systems (MEMS, piezoelectricity), and non-volatile memory (NVM, ferroelectricity). Realizing these modern devices often requires perovskite-based ferroelectric films thinner than 100 nm. Two such technologically important material systems are (Ba,Sr)TiO3 (BST), for tunable dielectric devices employed in wireless communications, and Pb(Zr,Ti)O3 (PZT), for ferroelectric non-volatile memory (FeRAM). In general, the material behavior is strongly influenced by the mechanical boundary conditions imposed by the substrate and surrounding layers and may vary considerably from the known bulk behavior. A better mechanistic understanding of these effects is essential for harnessing the full potential of ferroelectric thin-films and further optimizing existing devices. Both materials share a common crystal structure and similar properties, but face unique challenges due to the design parameters of these different applications. Tunable devices often require very low dielectric loss as well as large dielectric tunability. Present results show that the dielectric response of BST thin-films can either resemble a dipole-relaxor or follow the accepted empirical Universal Relaxation Law (Curie-von Schweidler), depending on temperature. These behaviors in a single ferroelectric thin-film system are often thought to be mutually exclusive. In state-of-the-art high density FeRAM, the ferroelectric polarization is at least as important as the dielectric response. It was found that these properties are significantly affected by moderate biaxial tensile and compressive stresses which reversibly alter the ferroelastic domain populations of PZT at room temperature. The 90-degree domain wall motion observed by high resolution synchrotron x-ray diffraction indicates that a small effective restoring stress of about 1 MPa acts on the domain walls in these nano-crystalline PZT films. This insight allows reversible control of the ferroelectric and dielectric behavior of these important functional oxide materials, with important implications for associated integrated devices.

Computational study of textured ferroelectric polycrystals: Dielectric and piezoelectric properties of template-matrix composites

NASA Astrophysics Data System (ADS)

Zhou, Jie E.; Yan, Yongke; Priya, Shashank; Wang, Yu U.

2017-01-01

Quantitative relationships between processing, microstructure, and properties in textured ferroelectric polycrystals and the underlying responsible mechanisms are investigated by phase field modeling and computer simulation. This study focuses on three important aspects of textured ferroelectric ceramics: (i) grain microstructure evolution during templated grain growth processing, (ii) crystallographic texture development as a function of volume fraction and seed size of the templates, and (iii) dielectric and piezoelectric properties of the obtained template-matrix composites of textured polycrystals. Findings on the third aspect are presented here, while an accompanying paper of this work reports findings on the first two aspects. In this paper, the competing effects of crystallographic texture and template seed volume fraction on the dielectric and piezoelectric properties of ferroelectric polycrystals are investigated. The phase field model of ferroelectric composites consisting of template seeds embedded in matrix grains is developed to simulate domain evolution, polarization-electric field (P-E), and strain-electric field (ɛ-E) hysteresis loops. The coercive field, remnant polarization, dielectric permittivity, piezoelectric coefficient, and dissipation factor are studied as a function of grain texture and template seed volume fraction. It is found that, while crystallographic texture significantly improves the polycrystal properties towards those of single crystals, a higher volume fraction of template seeds tends to decrease the electromechanical properties, thus canceling the advantage of ferroelectric polycrystals textured by templated grain growth processing. This competing detrimental effect is shown to arise from the composite effect, where the template phase possesses material properties inferior to the matrix phase, causing mechanical clamping and charge accumulation at inter-phase interfaces between matrix and template inclusions. The computational results are compared with complementary experiments, where good agreement is obtained.

Effects of crystallization on structural and dielectric properties of thin amorphous films of (1 - x)BaTiO3-xSrTiO3 (x=0-0.5, 1.0)

NASA Astrophysics Data System (ADS)

Kawano, H.; Morii, K.; Nakayama, Y.

1993-05-01

The possibilities for fabricating solid solutions of (Ba1-x,Srx)TiO3 (x≤0.5,1.0) by crystallization of amorphous films and for improving their dielectric properties by adjusting the Sr content were investigated. Thin amorphous films were prepared from powder targets consisting of mixtures of BaTiO3 and SrTiO3 by sputtering with a neutralized Ar-ion beam. The amorphous films crystallized into (Ba1-x, Srx)TiO3 solid solutions with a cubic perovskite-type structure after annealing in air at 923 K for more than 1 h. The Debye-type dielectric relaxation was observed for the amorphous films, whereas the crystallized films showed paraelectric behavior. The relative dielectric constants were of the order of 20 for the amorphous samples, but increased greatly after crystallization to about 60-200, depending on the composition; a larger increase in the dielectric constant was observed in the higher Sr content films, in the range x≤0.5, which could be correlated with an increase in the grain size of the crystallites. The crystallization processes responsible for the difference in the grain size are discussed based on the microstructural observations.

Dielectric and magnetic properties of FE- and Nb-doped CaCu3Ti4O12.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grubbs, Robert K.; Clem, Paul Gilbert; Samara, George A.

2005-08-01

Detailed studies of the properties of ceramic CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) have clarified the physics of this interesting material and revealed several features not reported before. The dielectric relaxational properties of CCTO are explained in terms of a capacitive-layer model, as for an inhomogeneous semiconductor, consisting of semiconducting grains and insulating grain boundaries as also concluded by others. The kinetics of the main [low-temperature (T)] relaxation reveal that two different thermally activated processes in CCTO grains control the dynamics. A likely candidate defect responsible for the two processes is the oxygen vacancy which is a double donor. A higher-Tmore » relaxation is determined by grain boundary conduction. Both Nb and Fe doping lowered both the apparent dielectric constant {var_epsilon}{prime} and the dielectric loss, but increased Fe doping led to more dramatic effects. At 3 at.% Fe doping, the anomalous {var_epsilon}{prime}(T) response was removed, making the CCTO an intrinsic, very-low-loss dielectric. The intrinsic {var_epsilon}{prime}({approx}75) and its T dependence are measured and shown to be largely determined by a low-lying soft TO phonon. At low T, cubic CCTO transforms into an antiferromagnetic phase at T{sub N} = 25 K. T{sub N} is essentially independent of Nb doping (up to 4 at.%) and of hydrostatic pressure (up to {approx}7 kbar), but decreases significantly with Fe doping. Analysis of the high-T dependence of the magnetic susceptibility provided insight into the role of Fe as a dopant. Finally, an {var_epsilon}{prime}(T) anomaly associated with the onset of antiferromagnetic order has been discovered, providing evidence for coupling between the polarization and sublattice magnetization. The possible origin of this coupling is discussed.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mukul M. Sharma; Steven L. Bryant; Carlos Torres-Verdin

The petrophysical properties of rocks, particularly their relative permeability and wettability, strongly influence the efficiency and the time-scale of all hydrocarbon recovery processes. However, the quantitative relationships needed to account for the influence of wettability and pore structure on multi-phase flow are not yet available, largely due to the complexity of the phenomena controlling wettability and the difficulty of characterizing rock properties at the relevant length scales. This project brings together several advanced technologies to characterize pore structure and wettability. Grain-scale models are developed that help to better interpret the electric and dielectric response of rocks. These studies allow themore » computation of realistic configurations of two immiscible fluids as a function of wettability and geologic characteristics. These fluid configurations form a basis for predicting and explaining macroscopic behavior, including the relationship between relative permeability, wettability and laboratory and wireline log measurements of NMR and dielectric response. Dielectric and NMR measurements have been made show that the response of the rocks depends on the wetting and flow properties of the rock. The theoretical models can be used for a better interpretation and inversion of standard well logs to obtain accurate and reliable estimates of fluid saturation and of their producibility. The ultimate benefit of this combined theoretical/empirical approach for reservoir characterization is that rather than reproducing the behavior of any particular sample or set of samples, it can explain and predict trends in behavior that can be applied at a range of length scales, including correlation with wireline logs, seismic, and geologic units and strata. This approach can substantially enhance wireline log interpretation for reservoir characterization and provide better descriptions, at several scales, of crucial reservoir flow properties that govern oil recovery.« less

Dielectric relaxation and localized electron hopping in colossal dielectric (Nb,In)-doped TiO2 rutile nanoceramics.

PubMed

Tsuji, Kosuke; Han, HyukSu; Guillemet-Fritsch, Sophie; Randall, Clive A

2017-03-28

Dielectric spectroscopy was performed on a Nb and In co-doped rutile TiO 2 nano-crystalline ceramic (n-NITO) synthesized by a low-temperature spark plasma sintering (SPS) technique. The dielectric properties of the n-NITO were not largely affected by the metal electrode contacts. Huge dielectric relaxation was observed at a very low temperature below 35 K. Both the activation energy and relaxation time suggested that the electronic hopping motion is the underlying mechanism responsible for the colossal dielectric permittivity (CP) and its relaxation, instead of the internal barrier layer effect or a dipolar relaxation. With Havriliak-Negami (H-N) fitting, a relaxation time with a large distribution of dielectric relaxations was revealed. The broad distributed relaxation phenomena indicated that Nb and In were involved, controlling the dielectric relaxation by modifying the polarization mechanism and localized states. The associated distribution function is calculated and presented. The frequency-dependent a.c. conductance is successfully explained by a hopping conduction model of the localized electrons with the distribution function. It is demonstrated that the dielectric relaxation is strongly correlated with the hopping electrons in the localized states. The CP in SPS n-NITO is then ascribed to a hopping polarization.

Pyroelectric response mechanism of barium strontium titanate ceramics in dielectric bolometer mode: The underlying essence of the enhancing effect of direct current bias field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mao, Chaoliang; Cao, Sheng; Yan, Shiguang

Pyroelectric response mechanism of Ba{sub 0.70}Sr{sub 0.30}TiO{sub 3} ceramics under dielectric bolometer (DB) mode was investigated by dielectric and pyroelectric properties measurement. The variations of total, intrinsic, and induced pyroelectric coefficients (p{sub tot}, p{sub int}, p{sub ind}) with temperatures and bias fields were analyzed. p{sub int} plays the dominant role to p{sub tot} through most of the temperature range and p{sub ind} will be slightly higher than p{sub int} above T{sub 0}. The essence of the enhancing effect of DC bias field on pyroelectric coefficient can be attributed to the high value of p{sub int}. This mechanism is useful formore » the pyroelectric materials (DB mode) applications.« less

Dielectric function of two-phase colloid-polymer nanocomposite.

PubMed

Mitzscherling, S; Cui, Q; Koopman, W; Bargheer, M

2015-11-28

The plasmon resonance of metal nanoparticles determines their optical response in the visible spectral range. Many details such as the electronic properties of gold near the particle surface and the local environment of the particles influence the spectra. We show how the cheap but highly precise fabrication of composite nanolayers by spin-assisted layer-by-layer deposition of polyelectrolytes can be used to investigate the spectral response of gold nanospheres (GNS) and gold nanorods (GNR) in a self-consistent way, using the established Maxwell-Garnett effective medium (MGEM) theory beyond the limit of homogeneous media. We show that the dielectric function of gold nanoparticles differs from the bulk value and experimentally characterize the shape and the surrounding of the particles thoroughly by SEM, AFM and ellipsometry. Averaging the dielectric functions of the layered surrounding by an appropriate weighting with the electric field intensity yields excellent agreement for the spectra of several nanoparticles and nanorods with various cover-layer thicknesses.

Develop Roll-to-Roll Manufacturing Process of ZrO 2 Nanocrystals/Acrylic Nanocomposites for High Refractive Index Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Pooran C.; Compton, Brett G.; Li, Jianlin

2015-04-01

The purpose of this Cooperative Research and Development Agreement (CRADA) was to develop and evaluate ZrO 2/acrylic nanocomposite coatings for integrated optoelectronic applications. The formulations engineered to be compatible with roll-to-roll process were evaluated in terms of optical and dielectric properties. The uniform distribution of the ZrO 2 nanocrystals in the polymer matrix resulted in highly tunable refractive index and dielectric response suitable for advanced photonic and electronic device applications.

Review of temperature dependence of thermal properties, dielectric properties, and perfusion of biological tissues at hyperthermic and ablation temperatures.

PubMed

Rossmanna, Christian; Haemmerich, Dieter

2014-01-01

The application of supraphysiological temperatures (>40°C) to biological tissues causes changes at the molecular, cellular, and structural level, with corresponding changes in tissue function and in thermal, mechanical and dielectric tissue properties. This is particularly relevant for image-guided thermal treatments (e.g. hyperthermia and thermal ablation) delivering heat via focused ultrasound (FUS), radiofrequency (RF), microwave (MW), or laser energy; temperature induced changes in tissue properties are of relevance in relation to predicting tissue temperature profile, monitoring during treatment, and evaluation of treatment results. This paper presents a literature survey of temperature dependence of electrical (electrical conductivity, resistivity, permittivity) and thermal tissue properties (thermal conductivity, specific heat, diffusivity). Data of soft tissues (liver, prostate, muscle, kidney, uterus, collagen, myocardium and spleen) for temperatures between 5 to 90°C, and dielectric properties in the frequency range between 460 kHz and 3 GHz are reported. Furthermore, perfusion changes in tumors including carcinomas, sarcomas, rhabdomyosarcoma, adenocarcinoma and ependymoblastoma in response to hyperthmic temperatures up to 46°C are presented. Where appropriate, mathematical models to describe temperature dependence of properties are presented. The presented data is valuable for mathematical models that predict tissue temperature during thermal therapies (e.g. hyperthermia or thermal ablation), as well as for applications related to prediction and monitoring of temperature induced tissue changes.

Review of temperature dependence of thermal properties, dielectric properties, and perfusion of biological tissues at hyperthermic and ablation temperatures

PubMed Central

Rossmann, Christian; Haemmerich, Dieter

2016-01-01

The application of supraphysiological temperatures (>40°C) to biological tissues causes changes at the molecular, cellular, and structural level, with corresponding changes in tissue function and in thermal, mechanical and dielectric tissue properties. This is particularly relevant for image-guided thermal treatments (e.g. hyperthermia and thermal ablation) delivering heat via focused ultrasound (FUS), radiofrequency (RF), microwave (MW), or laser energy; temperature induced changes in tissue properties are of relevance in relation to predicting tissue temperature profile, monitoring during treatment, and evaluation of treatment results. This paper presents a literature survey of temperature dependence of electrical (electrical conductivity, resistivity, permittivity) and thermal tissue properties (thermal conductivity, specific heat, diffusivity). Data of soft tissues (liver, prostate, muscle, kidney, uterus, collagen, myocardium and spleen) for temperatures between 5 to 90°C, and dielectric properties in the frequency range between 460 kHz and 3 GHz are reported. Furthermore, perfusion changes in tumors including carcinomas, sarcomas, rhabdomyosarcoma, adenocarcinoma and ependymoblastoma in response to hyperthmic temperatures up to 46°C are presented. Where appropriate, mathematical models to describe temperature dependence of properties are presented. The presented data is valuable for mathematical models that predict tissue temperature during thermal therapies (e.g. hyperthermia or thermal ablation), as well as for applications related to prediction and monitoring of temperature induced tissue changes. PMID:25955712

Machine learning aided diagnosis of hepatic malignancies through in vivo dielectric measurements with microwaves.

PubMed

Yilmaz, Tuba; Kılıç, Mahmut Alp; Erdoğan, Melike; Çayören, Mehmet; Tunaoğlu, Doruk; Kurtoğlu, İsmail; Yaslan, Yusuf; Çayören, Hüseyin; Arkan, Akif Enes; Teksöz, Serkan; Cancan, Gülden; Kepil, Nuray; Erdamar, Sibel; Özcan, Murat; Akduman, İbrahim; Kalkan, Tunaya

2016-06-20

In the past decade, extensive research on dielectric properties of biological tissues led to characterization of dielectric property discrepancy between the malignant and healthy tissues. Such discrepancy enabled the development of microwave therapeutic and diagnostic technologies. Traditionally, dielectric property measurements of biological tissues is performed with the well-known contact probe (open-ended coaxial probe) technique. However, the technique suffers from limited accuracy and low loss resolution for permittivity and conductivity measurements, respectively. Therefore, despite the inherent dielectric property discrepancy, a rigorous measurement routine with open-ended coaxial probes is required for accurate differentiation of malignant and healthy tissues. In this paper, we propose to eliminate the need for multiple measurements with open-ended coaxial probe for malignant and healthy tissue differentiation by applying support vector machine (SVM) classification algorithm to the dielectric measurement data. To do so, first, in vivo malignant and healthy rat liver tissue dielectric property measurements are collected with open-ended coaxial probe technique between 500 MHz to 6 GHz. Cole-Cole functions are fitted to the measured dielectric properties and measurement data is verified with the literature. Malign tissue classification is realized by applying SVM to the open-ended coaxial probe measurements where as high as 99.2% accuracy (F1 Score) is obtained.

Electrical conductivity, dielectric response and space charge dynamics of an electroactive polymer with and without nanofiller reinforcement

NASA Astrophysics Data System (ADS)

Kochetov, R.; Tsekmes, I. A.; Morshuis, P. H. F.

2015-07-01

Electroactive polymers have gained considerable attention over the last 20 years for exhibiting a large displacement in response to electrical stimulation. The promising fields of application include wave energy converters, muscle-like actuators, sensors, robotics, and biomimetics. For an electrical engineer, electroactive polymers can be seen as a dielectric elastomer film or a compliant capacitor with a highly deformable elastomeric medium. If the elastomer is pre-stretched and pre-charged, a reduction of the tensile force lets the elastomer revert to its original form and increases the electrical potential. The light weight of electroactive polymers, low cost, high intrinsic breakdown strength, cyclical way of operation, reliable performance, and high efficiency can be exploited to utilize the elastomeric material as a transducer. The energy storage for a linear dielectric polymer is determined by its relative permittivity and the applied electric field. The latter is limited by the dielectric breakdown strength of the material. Therefore, to generate a high energy density of a flexible capacitor, the film must be used at the voltage level close to the material’s breakdown or inorganic particles with high dielectric permittivity which can be introduced into the polymer matrix. In the present study, silicone-titania elastomer nanocomposites were produced and the influence of nanoparticles on the macroscopic dielectric properties of the neat elastomer including space charge dynamics, complex permittivity, and electrical conductivity, were investigated.

Switching from visibility to invisibility via Fano resonances: theory and experiment.

PubMed

Rybin, Mikhail V; Filonov, Dmitry S; Belov, Pavel A; Kivshar, Yuri S; Limonov, Mikhail F

2015-03-05

Subwavelength structures demonstrate many unusual optical properties which can be employed for engineering of a new generation of functional metadevices, as well as controlled scattering of light and invisibility cloaking. Here we demonstrate that the suppression of light scattering for any direction of observation can be achieved for a uniform dielectric object with high refractive index, in a sharp contrast to the cloaking with multilayered plasmonic structures suggested previously. Our finding is based on the novel physics of cascades of Fano resonances observed in the Mie scattering from a homogeneous dielectric rod. We observe this effect experimentally at microwaves by employing high temperature-dependent dielectric permittivity of a glass cylinder with heated water. Our results open a new avenue in analyzing the optical response of high-index dielectric nanoparticles and the physics of cloaking.

Switching from Visibility to Invisibility via Fano Resonances: Theory and Experiment

PubMed Central

Rybin, Mikhail V.; Filonov, Dmitry S.; Belov, Pavel A.; Kivshar, Yuri S.; Limonov, Mikhail F.

2015-01-01

Subwavelength structures demonstrate many unusual optical properties which can be employed for engineering of a new generation of functional metadevices, as well as controlled scattering of light and invisibility cloaking. Here we demonstrate that the suppression of light scattering for any direction of observation can be achieved for a uniform dielectric object with high refractive index, in a sharp contrast to the cloaking with multilayered plasmonic structures suggested previously. Our finding is based on the novel physics of cascades of Fano resonances observed in the Mie scattering from a homogeneous dielectric rod. We observe this effect experimentally at microwaves by employing high temperature-dependent dielectric permittivity of a glass cylinder with heated water. Our results open a new avenue in analyzing the optical response of high-index dielectric nanoparticles and the physics of cloaking. PMID:25739324

Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films

PubMed Central

2011-01-01

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated. PMID:21711646

Anomalous bias-stress-induced unstable phenomena of InZnO thin-film transistors using Ta2O5 gate dielectric

NASA Astrophysics Data System (ADS)

Xu, Wangying; Dai, Mingzhi; Liang, Lingyan; Liu, Zhimin; Sun, Xilian; Wan, Qing; Cao, Hongtao

2012-05-01

InZnO thin-film transistors using high-κ Ta2O5 gate dielectric are presented and analysed. The large capacitance coupling effect of amorphous Ta2O5 results in fabricated devices with good electrical properties. However, an anomalous negative threshold voltage (Vth) shift under positive bias stress is observed. It is suggested that electron detrapping from the high-κ Ta2O5 dielectric to the gate electrode is responsible for this Vth shift, which is supported both by the logarithmical dependence of the Vth change on the duration of the bias stress and device simulation extracted trapped charges involved.

Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Fiorenza, Patrick; Lo Nigro, Raffaella; Raineri, Vito

2011-12-01

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated.

Scanning Probe Microscopy on heterogeneous CaCu3Ti4O12 thin films.

PubMed

Fiorenza, Patrick; Lo Nigro, Raffaella; Raineri, Vito

2011-02-04

The conductive atomic force microscopy provided a local characterization of the dielectric heterogeneities in CaCu3Ti4O12 (CCTO) thin films deposited by MOCVD on IrO2 bottom electrode. In particular, both techniques have been employed to clarify the role of the inter- and sub-granular features in terms of conductive and insulating regions. The microstructure and the dielectric properties of CCTO thin films have been studied and the evidence of internal barriers in CCTO thin films has been provided. The role of internal barriers and the possible explanation for the extrinsic origin of the giant dielectric response in CCTO has been evaluated.

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

PubMed

Prateek; Thakur, Vijay Kumar; Gupta, Raju Kumar

2016-04-13

Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers or polymer matrix help in further improving the dielectric properties as compared to two-phase nanocomposites. Recent research has been focused on altering the dielectric properties of different materials while also maintaining their superior flexibility. Flexible polymer nanocomposites are the best candidates for application in various fields. However, certain challenges still present, which can be solved only by extensive research in this field.

Influence of color on dielectric properties of marinated poultry breast meat.

PubMed

Samuel, D; Trabelsi, S

2012-08-01

The dielectric behavior of foods when exposed to radio-frequency and microwave electric fields is highly influenced by moisture content and the degree of water binding with constituents of the food materials. The ability to correlate specific food quality characteristics with the dielectric properties can lead to the development of rapid, nondestructive techniques for such quality measurements. Water-holding capacity is a critical attribute in meat quality. Up to 50% of raw poultry meat in the United States is marinated with mixtures of water, salts, and phosphates. The objective of this study was to determine if variations in breast meat color would affect the dielectric properties of marinated poultry meat over a broad frequency range from 500 MHz to 50 GHz. Poultry meat was obtained from a local commercial plant in Georgia (USA). Color and pH measurements were taken on the breast filets. Groups of breast filets were sorted into classes of pale and normal before adding marination pickup percentages of 0, 5, 10, and 15. Breast filets were vacuum-tumbled and weighed for pickup percentages. Dielectric properties of the filets were measured with a coaxial open-ended probe on samples equilibrated to 25°C. Samples from pale meat exhibited higher dielectric properties than samples from normal meat. No differences could be observed between samples from pale and normal meat after marination of the samples. Overall, dielectric properties increased as the marination pickup increased (α=0.05). Marination pickup strongly influenced the dielectric loss factor. Differences between samples marinated at different pickup levels were more pronounced at lower frequencies for the dielectric loss factor. As frequency increased, the differences between samples decreased. Differences in dielectric constant between samples were not as consistent as those seen with the dielectric loss factor.

Modeling of the dielectric permittivity of porous soil media with water using statistical-physical models

NASA Astrophysics Data System (ADS)

Usowicz, Boguslaw; Marczewski, Wojciech; Usowicz, Jerzy B.; Łukowski, Mateusz; Lipiec, Jerzy; Stankiewicz, Krystyna

2013-04-01

Radiometric observations with SMOS rely on the Radiation Transfer Equations (RTE) determining the Brightness Temperature (BT) in two linear polarization components (H, V) satisfying Fresnel principle of propagation in horizontally layered target media on the ground. RTE involve variables which bound the equations expressed in Electro-Magnetic (EM) terms of the intensity BT to the physical reality expressed by non-EM variables (Soil Moisture (SM), vegetation indexes, fractional coverage with many different properties, and the boundary conditions like optical thickness, layer definitions, roughness, etc.) bridging the EM domain to other physical aspects by means of the so called tau-omega methods. This method enables joining variety of different valuable models, including specific empirical estimation of physical properties in relation to the volumetric water content. The equations of RTE are in fact expressed by propagation, reflection and losses or attenuation existing on a considered propagation path. The electromagnetic propagation is expressed in the propagation constant. For target media on the ground the dielectric constant is a decisive part for effects of propagation. Therefore, despite of many various physical parameters involved, one must effectively and dominantly rely on the dielectric constant meant as a complex variable. The real part of the dielectric constant represents effect of apparent shortening the propagation path and the refraction, while the imaginary part is responsible for the attenuation or losses. This work engages statistical-physical modeling of soil properties considering the media as a mixture of solid grains, and gas or liquid filling of pores and contact bridges between compounds treated statistically. The method of this modeling provides an opportunity of characterizing the porosity by general statistical means, and is applicable to various physical properties (thermal, electrical conductivity and dielectric properties) which depend on composition of compounds. The method was developed beyond the SMOS method, but they meet just in RTE, at the dielectric constant. The dielectric constant is observed or measured (retrieved) by SMOS, regardless other properties like the soil porosity and without a direct relation to thermal properties of soils. Relations between thermal properties of soil to the water content are very consistent. Therefore, we took a concept of introducing effects of the soil porosity, and thermal properties of soils into the representation of the dielectric constant in complex measures, and thus gaining new abilities for capturing effects of the porosity by the method of SMOS observations. Currently we are able presenting few effects of relations between thermal properties and the soil moisture content, on examples from wetlands Biebrza and Polesie in Poland, and only search for correlations between SM from SMOS to the moisture content known from the ground. The correlations are poor for SMOS L2 data processed with the version of retrievals using the model of Dobson (501), but we expect more correlation for the version using the model of Mironov (551). If the supposition is confirmed, then we may gain encouragement to employing the statistical-physical modeling of the dielectric constant and thermal properties for the purposes of using this model in RTE and tau-omega method. Treating the soil porosity for a target of research directly is not enough strongly motivated like the use of effects on SM observable in SMOS.

Unique dielectric tunability of Pb0.99[(Zr0.6Sn0.4)0.94Ti0.06]0.98Nb0.02O3 antiferroelectric ceramics

NASA Astrophysics Data System (ADS)

Li, Lei; Spreitzer, Matjaž; Suvorov, Danilo; Chen, Xiang Ming

2016-08-01

The tunable dielectric properties of Pb0.99[(Zr0.6Sn0.4)0.94Ti0.06]0.98Nb0.02O3 antiferroelectric ceramics were investigated, and high relative tunability of 49% was obtained at 25 °C under a low bias electric field of 50 kV/cm. Abrupt changes and a significant hysteresis in dielectric constant and dielectric loss against bias electric field were observed, which are very different from the previously reported antiferroelectric materials. The unique dielectric tunability is attributed to the square-shaped double hysteresis loop and indicates the possible applications in some special tunable devices, such as an electrically-controlled switch. Pb0.99[(Zr0.6Sn0.4)0.94Ti0.06]0.98Nb0.02O3 ceramics also exhibit unique dielectric tunability at -5 °C. Abrupt changes in dielectric constant and dielectric loss were observed when the bias electric field increased to 31 kV/cm for the fresh sample, which is similar to the antiferroelectric-like dielectric tunability at 25 °C. However, the dielectric tunability was ferroelectric-like in the following measurement. This response is consistent with the hysteresis loop and can be explained by the electric field-assisted irreversible antiferroelectric-ferroelectric phase transition.

Focus Article: Oscillatory and long-range monotonic exponential decays of electrostatic interactions in ionic liquids and other electrolytes: The significance of dielectric permittivity and renormalized charges

NASA Astrophysics Data System (ADS)

Kjellander, Roland

2018-05-01

A unified treatment of oscillatory and monotonic exponential decays of interactions in electrolytes is displayed, which highlights the role of dielectric response of the fluid in terms of renormalized (effective) dielectric permittivity and charges. An exact, but physically transparent statistical mechanical formalism is thereby used, which is presented in a systematic, pedagogical manner. Both the oscillatory and monotonic behaviors are given by an equation for the decay length of screened electrostatic interactions that is very similar to the classical expression for the Debye length. The renormalized dielectric permittivities, which have similar roles for electrolytes as the dielectric constant has for pure polar fluids, consist in general of several entities with different physical meanings. They are connected to dielectric response of the fluid on the same length scale as the decay length of the screened interactions. Only in cases where the decay length is very long, these permittivities correspond approximately to a dielectric response in the long-wavelength limit, like the dielectric constant for polar fluids. Experimentally observed long-range exponentially decaying surface forces are analyzed as well as the oscillatory forces observed for short to intermediate surface separations. Both occur in some ionic liquids and in concentrated as well as very dilute electrolyte solutions. The coexisting modes of decay are in general determined by the bulk properties of the fluid and not by the solvation of the surfaces; in the present cases, they are given by the behavior of the screened Coulomb interaction of the bulk fluid. The surface-fluid interactions influence the amplitudes and signs or phases of the different modes of the decay, but not their decay lengths and wavelengths. The similarities between some ionic liquids and very dilute electrolyte solutions as regards both the long-range monotonic and the oscillatory decays are analyzed.

Thermal and ac electrical properties of N-methylanthranilic acid below room temperature

NASA Astrophysics Data System (ADS)

Abdel-Kader, M. M.; Basha, M. A. F.; Ramzy, G. H.; Aboud, A. I.

2018-06-01

In this study, we investigated the thermal and alternating current (ac) electrical properties of N-methylanthranilic acid. Based on data obtained by differential scanning calorimetry, we detected two endothermic transitions at ≈ 213 K and ≈265.41 K. The weakening of hydrogen bonds as the temperature increased appeared to be the main cause of these phase transitions. We also recorded the melting point at about 475.5 K. Both the ac conductivity (σac) and complex dielectric constant (ε∗ = ε ' - jε ' ') were studied as functions of temperature over the frequency range from 1 kHz to 100 kHz. We observed significant variations in the thermal and electrical properties before and after the transition temperature at 265.41 K. The conduction mechanism responsible for the ac electrical properties before this transition was due to overlapping large polarons. These novel results are expected to have impacts on the application of organic semiconductors and dielectrics.

Dielectric properties of (SWCNTs)x GdBa2CuO7-δ superconductor nanocomposites

NASA Astrophysics Data System (ADS)

Anas, M.; Ebrahim, S.; Eldeen, I. G.; Awad, R.; Abou-Aly, A. I.

2017-11-01

Gd-123 superconducting phase was prepared by solid-state reaction technique. Single-walled carbon nanotubes (SWCNTs) were added in Gd-123 superconducting matrix with different concentrations during the final sintering process to obtain (SWCNTs)x GdBa2Cu3O7-δ (x = 0.0-0.1 wt.%) nanoparticles-superconductor composite. The influence of SWCNTs addition on the phase formation, structural, morphological, superconducting and dielectric properties of Gd-123 phase was investigated. It was found that SWCNTs addition enhance the phase formation and does not change the crystal structure of the host Gd-123 superconducting phase. The superconducting properties of Gd-123 samples were improved after the addition of SWCNTs up to x = 0.06 wt.% due to the enhancement in intergrain connectivity by healing up of micro-cracks and reduction of defects, while these properties were retarded with further increase in x. The dielectric response of (SWCNTs)x Gd-123 superconducting phase with x = 0.0, 0.01, 0.04, 0.05, 0.06 and 0.1 wt.% was measured from 100 KHz to 5 MHz at 77 K. The results reveal that for both real (𝜀‧) and imaginary (𝜀″) parts of dielectric constant, the frequency of dispersion increased by increasing SWCNTs amount up to 0.06 wt.%, then this frequency shifted to lower values for x > 0.06 wt.%. The results were discussed according to the presence and interference of both interfacial and dipolar polarizations.

Optical and microwave dielectric properties of pulsed laser deposited Na{sub 0.5}Bi{sub 0.5}TiO{sub 3} thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joseph, Andrews; Goud, J. Pundareekam; Raju, K. C. James

2016-05-23

Optical properties of pulsed laser deposited (PLD) sodium bismuth titanate thin films (NBT), are investigated at wavelengths of 190-2500 nm. Microwave dielectric properties were investigated using the Split Post Dielectric Resonator (SPDR) technique. At 10 GHz, the NBT films have a dielectric constant of 205 and loss tangent of 0.0373 at room temperature. The optical spectra analysis reveals that NBT thin films have an optical band gap E{sub g}=3.55 eV and it has a dielectric constant of 3.37 at 1000 nm with dielectric loss of 0.299. Hence, NBT is a promising candidate for photonic device applications.

Controlling Crystal Microstructure to Minimize Loss in Polymer Dielectrics

NASA Astrophysics Data System (ADS)

Miranda, Daniel; Iacob, Ciprian; Zhang, Shihai; Runt, James

Polymer dielectric films are of great importance for high performance capacitors. For these films it is critical to reduce dielectric loss, as it diminishes efficiency and contributes to waste heat generation during device operation. Here, a model semi-crystalline polymer, poly(ethylene naphthalate) (PEN), was used to examine how morphological factors inhibit chain relaxations responsible for loss. This was achieved by manipulating the extent of crystallization and the crystalline microstructure through a combination of annealing and uniaxial drawing, and investigating their effects on dielectric performance. Varying crystallization conditions influenced the dynamic Tg and extent of rigid amorphous fraction formation, but had a limited effect on loss magnitude. Film orientation however greatly reduced loss, through strain-induced crystallization and development of oriented amorphous mesophasic regions. Post-drawing annealing conditions were capable of further refining the crystal microstructure and, in turn, the dielectric properties. These findings demonstrate that semi-crystalline polymer morphology has a very strong influence on amorphous chain relaxations, and understanding how processing conditions affect morphology is critical to the rational design of polymer dielectrics. Office of Naval Research.

Average Dielectric Property Analysis of Complex Breast Tissue with Microwave Transmission Measurements

PubMed Central

Garrett, John D.; Fear, Elise C.

2015-01-01

Prior information about the average dielectric properties of breast tissue can be implemented in microwave breast imaging techniques to improve the results. Rapidly providing this information relies on acquiring a limited number of measurements and processing these measurement with efficient algorithms. Previously, systems were developed to measure the transmission of microwave signals through breast tissue, and simplifications were applied to estimate the average properties. These methods provided reasonable estimates, but they were sensitive to multipath. In this paper, a new technique to analyze the average properties of breast tissues while addressing multipath is presented. Three steps are used to process transmission measurements. First, the effects of multipath were removed. In cases where multipath is present, multiple peaks were observed in the time domain. A Tukey window was used to time-gate a single peak and, therefore, select a single path through the breast. Second, the antenna response was deconvolved from the transmission coefficient to isolate the response from the tissue in the breast interior. The antenna response was determined through simulations. Finally, the complex permittivity was estimated using an iterative approach. This technique was validated using simulated and physical homogeneous breast models and tested with results taken from a recent patient study. PMID:25585106

Dielectric properties for prediction of moisture content in Vidalia onions

USDA-ARS?s Scientific Manuscript database

Microwave Sensing provides a means for nondestructively determining the amount of moisture in materials by sensing the dielectric properties of the material. In this study, dielectric properties of Vidalia onions were analyzed for moisture dependence at 13.36 GHz and 23°C for moisture content betwee...

A large-scale study of the ultrawideband microwave dielectric properties of normal breast tissue obtained from reduction surgeries.

PubMed

Lazebnik, Mariya; McCartney, Leah; Popovic, Dijana; Watkins, Cynthia B; Lindstrom, Mary J; Harter, Josephine; Sewall, Sarah; Magliocco, Anthony; Booske, John H; Okoniewski, Michal; Hagness, Susan C

2007-05-21

The efficacy of emerging microwave breast cancer detection and treatment techniques will depend, in part, on the dielectric properties of normal breast tissue. However, knowledge of these properties at microwave frequencies has been limited due to gaps and discrepancies in previously reported small-scale studies. To address these issues, we experimentally characterized the wideband microwave-frequency dielectric properties of a large number of normal breast tissue samples obtained from breast reduction surgeries at the University of Wisconsin and University of Calgary hospitals. The dielectric spectroscopy measurements were conducted from 0.5 to 20 GHz using a precision open-ended coaxial probe. The tissue composition within the probe's sensing region was quantified in terms of percentages of adipose, fibroconnective and glandular tissues. We fit a one-pole Cole-Cole model to the complex permittivity data set obtained for each sample and determined median Cole-Cole parameters for three groups of normal breast tissues, categorized by adipose tissue content (0-30%, 31-84% and 85-100%). Our analysis of the dielectric properties data for 354 tissue samples reveals that there is a large variation in the dielectric properties of normal breast tissue due to substantial tissue heterogeneity. We observed no statistically significant difference between the within-patient and between-patient variability in the dielectric properties.

Effect of V2O5 Addition on the Phase Composition of Bi5FeTi3O15 Ceramic and RF/Microwave Dielectric Properties

NASA Astrophysics Data System (ADS)

Aguiar, F. A. A.; Sales, A. J. M.; Araújo, B. S.; Sabóia, K. D. A.; Filho, M. C. Campos; Sombra, A. S. B.; Ayala, A. P.; Fechine, P. B. A.

2017-04-01

Bi5FeTi3O15 (BFT) polycrystalline ceramic with the addition of different concentrations of V2O5 was obtained by a solid-state method. X-ray powder diffraction, Raman spectroscopy and scanning electron microscopy (SEM) were used to study the microstructure and crystalline phases of the ceramics. SEM images showed plate-like morphology with dimensions between 0.32 μm and 3.07 μm (grain size, average around 1.3 μm). For samples with V2O5 concentration below 5%, Raman spectra were mainly determined by the vibrational modes from BFT. Impedance spectroscopy was also performed to evaluate the dielectric properties at microwave and radio frequencies (RF). Two extra phases (Bi4V1.5Fe0.5O10.5 and Bi2Ti2O7) were found due to the chemical reaction between BFT and V2O5. These phases were responsible for the changes in the grain morphology and dielectric response. V2O5 addition increased the real part of the dielectric permittivity ( ɛ') and reduced the dielectric loss tangent (tan δ) values at the RF range of 10 Hz to 1 MHz. For microwave frequencies of 3-3.5 GHz, ɛ' and temperature coefficient of resonant frequency ( τ f) values ranged from 66.52 ppm/°C to 88.60 ppm/°C and -304.3 ppm/°C to -192.6 ppm/°C, respectively. Thereby, BFT ceramics with added V2O5 are good candidates to be used for microwave devices (e.g., cell phones).

Computational screening of organic polymer dielectrics for novel accelerator technologies

DOE PAGES

Pilania, Ghanshyam; Weis, Eric; Walker, Ethan M.; ...

2018-06-18

The use of infrared lasers to power accelerating dielectric structures is a developing area of research. Within this technology, the choice of the dielectric material forming the accelerating structures, such as the photonic band gap (PBG) structures, is dictated by a range of interrelated factors including their dielectric and optical properties, amenability to photo-polymerization, thermochemical stability and other target performance metrics of the particle accelerator. In this direction, electronic structure theory aided computational screening and design of dielectric materials can play a key role in identifying potential candidate materials with the targeted functionalities to guide experimental synthetic efforts. In anmore » attempt to systematically understand the role of chemistry in controlling the electronic structure and dielectric properties of organic polymeric materials, here we employ empirical screening and density functional theory (DFT) computations, as a part of our multi-step hierarchal screening strategy. Our DFT based analysis focused on the bandgap, dielectric permittivity, and frequency-dependent dielectric losses due to lattice absorption as key properties to down-select promising polymer motifs. In addition to the specific application of dielectric laser acceleration, the general methodology presented here is deemed to be valuable in the design of new insulators with an attractive combination of dielectric properties.« less

Temperature dependence of the dielectric properties of rubber wood

Treesearch

Mohammed Firoz Kabir; Wan M. Daud; Kaida B. Khalid; Haji A.A. Sidek

2001-01-01

The effect of temperature on the dielectric properties of rubber wood was investigated in three anisotropic directions—longitudinal, radial, and tangential, and at different measurement frequencies. Low frequency measurements were conducted with a dielectric spectrometer, and high frequencies used microwave applied with open-ended coaxial probe sensors. Dielectric...

Dielectric characterization of Bentonite clay at various moisture contents and with mixtures of biomass in the microwave spectrum

USDA-ARS?s Scientific Manuscript database

This study assesses the potential for using bentonite as a microwave absorber for microwave-assisted biomass pyrolysis based on the dielectric properties. Dielectric properties of bentonite at different moisture contents were measured using a coaxial line dielectric probe and vector network analyzer...

A Facile Strategy to Enhance the Dielectric and Mechanical Properties of MWCNTs/PVDF Composites with the Aid of MMA-co-GMA Copolymer

PubMed Central

Song, Shixin; Xia, Shan; Jiang, Shangkun; Lv, Xue; Sun, Shulin; Li, Quanming

2018-01-01

A facile strategy is adopted to prepare carboxylic functionalized multiwalled carbon nanotube (c-MWCNT) modified high dielectric constant (high-k) poly(vinylidene fluoride) (PVDF) composites with the aid of methyl methacrylate-co-glycidyl methacrylate copolymer (MG). The MG is miscible with PVDF and the epoxy groups of the copolymer can react with the carboxylic groups of c-MWCNT, which induce the uniform dispersion of c-MWCNT and a form insulator layer on the surface of c-MWCNT. The c-MWCNTs/MG/PVDF composites with 8 vol % c-MWCNT present excellent dielectric properties with high dielectric constant (~448) and low dielectric loss (~2.36) at the frequency of 1 KHz, the dielectric loss is much lower than the c-MWCNT/PVDF composites without MG. The obvious improvement in dielectric properties ascribes to the existence of MG, which impede the direct contact of c-MWCNTs and PVDF and avoid the formation of conductive network. Therefore, we propose a practical and simple strategy for preparing composites with excellent dielectric properties, which are promising for applications in electronics devices. PMID:29495491

A Facile Strategy to Enhance the Dielectric and Mechanical Properties of MWCNTs/PVDF Composites with the Aid of MMA-co-GMA Copolymer.

PubMed

Song, Shixin; Xia, Shan; Jiang, Shangkun; Lv, Xue; Sun, Shulin; Li, Quanming

2018-02-27

A facile strategy is adopted to prepare carboxylic functionalized multiwalled carbon nanotube (c-MWCNT) modified high dielectric constant (high- k ) poly(vinylidene fluoride) (PVDF) composites with the aid of methyl methacrylate-co-glycidyl methacrylate copolymer (MG). The MG is miscible with PVDF and the epoxy groups of the copolymer can react with the carboxylic groups of c-MWCNT, which induce the uniform dispersion of c-MWCNT and a form insulator layer on the surface of c-MWCNT. The c-MWCNTs/MG/PVDF composites with 8 vol % c-MWCNT present excellent dielectric properties with high dielectric constant (~448) and low dielectric loss (~2.36) at the frequency of 1 KHz, the dielectric loss is much lower than the c-MWCNT/PVDF composites without MG. The obvious improvement in dielectric properties ascribes to the existence of MG, which impede the direct contact of c-MWCNTs and PVDF and avoid the formation of conductive network. Therefore, we propose a practical and simple strategy for preparing composites with excellent dielectric properties, which are promising for applications in electronics devices.

Zn-Al layered double hydroxide prepared at different molar ratios: Preparation, characterization, optical and dielectric properties

NASA Astrophysics Data System (ADS)

Ahmed, Abdullah Ahmed Ali; Talib, Zainal Abidin; bin Hussein, Mohd Zobir; Zakaria, Azmi

2012-07-01

The co-precipitation method was used to prepare Zn-Al-NO3-LDH at different Zn2+/Al3+ molar ratios (2, 3, 4, 5 and 6) and pH value of 7.5. The structure, textural, composition and morphological properties were investigated using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) and scanning electron microscope (SEM), respectively. The crystallinity of LDH samples were found to improve as molar ratio decreased which is attributed to the distortion of the hydroxide layers networks of the LDH crystal by the larger difference in ionic radii of Zn2+ and Al3+. The optical band gap energy of LDH samples were evaluated using absorbance data from UV-Vis-NIR Diffuse reflectance spectroscopy. Band gaps were affected by the variation of the Zn2+/Al3+ molar ratio is due to the formation of the low crystalline phases (ZnO and ZnAl2O4). The water molecules and anionic NO3- in the LDH interlayer were responsible for the generation of the dielectric response. This response can be described by an anomalous low frequency dispersion using the second type of Universal Power Law. The dominance of ZnO dipoles and charge carriers (NO3- ions) in the dielectric relaxation increases with the increasing molar ratio.

Dielectric property study of poly(4-vinylphenol)-graphene oxide nanocomposite thin film

NASA Astrophysics Data System (ADS)

Roy, Dhrubojyoti

2018-05-01

Thin film capacitor device having a sandwich structure of indium tin oxide (ITO)-coated glass/polymer or polymer nanocomposite /silver has been fabricated and their dielectric and leakage current properties has been studied. The dielectric properties of the capacitors were characterized for frequencies ranging from 1 KHz to 1 MHz. 5 wt% Poly(4-vinylphenol)(PVPh)-Graphene (GO) nanocomposite exhibited an increase in dielectric constant to 5.6 and small rise in dielectric loss to around˜0.05 at 10 KHz w.r.t polymer. The DC conductivity measurements reveal rise of leakage current in nanocomposite.

Submillimeter and far-infrared dielectric properties of thin films

NASA Astrophysics Data System (ADS)

Cataldo, Giuseppe; Wollack, Edward J.

2016-07-01

The complex dielectric function enables the study of a material's refractive and absorptive properties and provides information on a material's potential for practical application. Commonly employed line shape profile functions from the literature are briefly surveyed and their suitability for representation of dielectric material properties are discussed. An analysis approach to derive a material's complex dielectric function from observed transmittance spectra in the far-infrared and submillimeter regimes is presented. The underlying model employed satisfies the requirements set by the Kramers-Kronig relations. The dielectric function parameters derived from this approachtypically reproduce the observed transmittance spectra with an accuracy of < 4%.

Zn-Al layered double hydroxide prepared at different molar ratios: Preparation, characterization, optical and dielectric properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Abdullah Ahmed Ali; Talib, Zainal Abidin, E-mail: zainalat@science.upm.edu.my; Zobir bin Hussein, Mohd

2012-07-15

The co-precipitation method was used to prepare Zn-Al-NO{sub 3}-LDH at different Zn{sup 2+}/Al{sup 3+} molar ratios (2, 3, 4, 5 and 6) and pH value of 7.5. The structure, textural, composition and morphological properties were investigated using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) and scanning electron microscope (SEM), respectively. The crystallinity of LDH samples were found to improve as molar ratio decreased which is attributed to the distortion of the hydroxide layers networks of the LDH crystal by the larger difference in ionic radii of Zn{sup 2+} and Al{sup 3+}. The optical band gap energymore » of LDH samples were evaluated using absorbance data from UV-Vis-NIR Diffuse reflectance spectroscopy. Band gaps were affected by the variation of the Zn{sup 2+}/Al{sup 3+} molar ratio is due to the formation of the low crystalline phases (ZnO and ZnAl{sub 2}O{sub 4}). The water molecules and anionic NO{sub 3}{sup -} in the LDH interlayer were responsible for the generation of the dielectric response. This response can be described by an anomalous low frequency dispersion using the second type of Universal Power Law. The dominance of ZnO dipoles and charge carriers (NO{sub 3}{sup -} ions) in the dielectric relaxation increases with the increasing molar ratio. - Graphical abstract: (a) Schematic diagram of Zn-Al- NO{sub 3}-LDH shows the LDH structure, (b) Kubelka-Munk transformed reflectance spectra and c. The dielectric constant versus frequency of Zn-Al- NO{sub 3}-LDH samples. Highlights: Black-Right-Pointing-Pointer Zn-Al-NO{sub 3}-LDH was prepared at different Zn{sup 2+}/Al{sup 3+} molar ratios (2, 3, 4, 5 and 6). Black-Right-Pointing-Pointer The crystallinity of LDH phase decreased with increase of Zn{sup 2+}/Al{sup 3+} molar ratio. Black-Right-Pointing-Pointer The optical band gaps of LDH samples have been measured. Black-Right-Pointing-Pointer Dielectric response of LDH can be described by anomalous low frequency dispersion.« less

Preparation of a Carbon Doped Tissue-Mimicking Material with High Dielectric Properties for Microwave Imaging Application

PubMed Central

Lan, Siang-Wen; Weng, Min-Hang; Yang, Ru-Yuan; Chang, Shoou-Jinn; Chung, Yaoh-Sien; Yu, Tsung-Chih; Wu, Chun-Sen

2016-01-01

In this paper, the oil-in-gelatin based tissue-mimicking materials (TMMs) doped with carbon based materials including carbon nanotube, graphene ink or lignin were prepared. The volume percent for gelatin based mixtures and oil based mixtures were both around 50%, and the doping amounts were 2 wt %, 4 wt %, and 6 wt %. The effect of doping material and amount on the microwave dielectric properties including dielectric constant and conductivity were investigated over an ultra-wide frequency range from 2 GHz to 20 GHz. The coaxial open-ended reflection technology was used to evaluate the microwave dielectric properties. Six measured values in different locations of each sample were averaged and the standard deviations of all the measured dielectric properties, including dielectric constant and conductivity, were less than one, indicating a good uniformity of the prepared samples. Without doping, the dielectric constant was equal to 23 ± 2 approximately. Results showed with doping of carbon based materials that the dielectric constant and conductivity both increased about 5% to 20%, and the increment was dependent on the doping amount. By proper selection of doping amount of the carbon based materials, the prepared material could map the required dielectric properties of special tissues. The proposed materials were suitable for the phantom used in the microwave medical imaging system. PMID:28773678

Analysis of capacitive force acting on a cantilever tip at solid/liquid interfaces

NASA Astrophysics Data System (ADS)

Umeda, Ken-ichi; Kobayashi, Kei; Oyabu, Noriaki; Hirata, Yoshiki; Matsushige, Kazumi; Yamada, Hirofumi

2013-04-01

Dielectric properties of biomolecules or biomembranes are directly related to their structures and biological activities. Capacitance force microscopy based on the cantilever deflection detection is a useful scanning probe technique that can map local dielectric constant. Here we report measurements and analysis of the capacitive force acting on a cantilever tip at solid/liquid interfaces induced by application of an alternating voltage to explore the feasibility of the measurements of local dielectric constant by the voltage modulation technique in aqueous solutions. The results presented here suggest that the local dielectric constant measurements by the conventional voltage modulation technique are basically possible even in polar liquid media. However, the cantilever deflection is not only induced by the electrostatic force, but also by the surface stress, which does not include the local dielectric information. Moreover, since the voltage applied between the tip and sample are divided by the electric double layer and the bulk polar liquid, the capacitive force acting on the apex of the tip are strongly attenuated. For these reasons, the lateral resolution in the local dielectric constant measurements is expected to be deteriorated in polar liquid media depending on the magnitude of dielectric response. Finally, we present the criteria for local dielectric constant measurements with a high lateral resolution in polar liquid media.

Characterization of dielectric properties of nanocellulose from wood and algae for electrical insulator applications.

PubMed

Le Bras, David; Strømme, Maria; Mihranyan, Albert

2015-05-07

Cellulose is one of the oldest electrically insulating materials used in oil-filled high-power transformers and cables. However, reports on the dielectric properties of nanocellulose for electrical insulator applications are scarce. The aim of this study was to characterize the dielectric properties of two nanocellulose types from wood, viz., nanofibrillated cellulose (NFC), and algae, viz., Cladophora cellulose, for electrical insulator applications. The cellulose materials were characterized with X-ray diffraction, nitrogen gas and moisture sorption isotherms, helium pycnometry, mechanical testing, and dielectric spectroscopy at various relative humidities. The algae nanocellulose sample was more crystalline and had a lower moisture sorption capacity at low and moderate relative humidities, compared to NFC. On the other hand, it was much more porous, which resulted in lower strength and higher dielectric loss than for NFC. It is concluded that the solid-state properties of nanocellulose may have a substantial impact on the dielectric properties of electrical insulator applications.

Effect of Shock Waves on Dielectric Properties of KDP Crystal

NASA Astrophysics Data System (ADS)

Sivakumar, A.; Suresh, S.; Pradeep, J. Anto; Balachandar, S.; Martin Britto Dhas, S. A.

2018-05-01

An alternative non-destructive approach is proposed and demonstrated for modifying electrical properties of crystal using shock-waves. The method alters dielectric properties of a potassium dihydrogen phosphate (KDP) crystal by loading shock-waves generated by a table-top shock tube. The experiment involves launching the shock-waves perpendicular to the (100) plane of the crystal using a pressure driven table-top shock tube with Mach number 1.9. Electrical properties of dielectric constant, dielectric loss, permittivity, impedance, AC conductivity, DC conductivity and capacitance as a function of spectrum of frequency from 1 Hz to 1 MHz are reported for both pre- and post-shock wave loaded conditions of the KDP crystal. The experimental results reveal that dielectric constant of KDP crystal is sensitive to the shock waves such that the value decreases for the shock-loaded KDP sample from 158 to 147. The advantage of the proposed approach is that it is an alternative to the conventional doping process for tailoring dielectric properties of this type of crystal.

Contributions of intrinsic and extrinsic polarization species to energy storage properties of Ba0.95Ca0.05Zr0.2Ti0.8O3 ceramics

NASA Astrophysics Data System (ADS)

Zhan, Di; Xu, Qing; Huang, Duan-Ping; Liu, Han-Xing; Chen, Wen; Zhang, Feng

2018-03-01

Ba0.95Ca0.05Zr0.2Ti0.8O3 ceramics were prepared at different sintering temperatures by citrate precursor and solid-state reaction methods, respectively. The crystal structure and microstructure of the specimens were characterized. In view of energy storage capacitor utilizations, the dielectric properties of the specimens were investigated at room temperature as a function of frequency and applied electric field. Moreover, the nature of mobile charge carriers in the specimens was diagnosed by complex impedance spectroscopy at elevated temperatures. While the dielectric constants of the specimens prepared by different methods are quite different (4.4 × 103-2.2 × 104 at 10 kHz) at zero electric field, the energy storage densities at an identical strong electric field are similar (e.g. 0.32-0.41 J/cm3 at 120 kV/cm). The dielectric constants under bias electric field were fitted to a multipolarization mechanism model to resolve the contributions of intrinsic and extrinsic polarization mechanisms. It turned out that the extrinsic contributions fade out within low electric field range (<20 kV/cm) and thereby the intrinsic lattice polarization governs the overall dielectric responses at higher fields. Based on the fitting result, the energy storage properties of the specimens were interpreted.

Novel photoswitchable dielectric properties on nanomaterials of electronic core-shell γ-FeOx@Au@fullerosomes for GHz frequency applications.

PubMed

Wang, Min; Su, Chefu; Yu, Tzuyang; Tan, Loon-Seng; Hu, Bin; Urbas, Augustine; Chiang, Long Y

2016-03-28

We unexpectedly observed a large amplification of the dielectric properties associated with the photoswitching effect and the new unusual phenomenon of delayed photoinduced capacitor-like (i.e. electric polarization) behavior at the interface on samples of three-layered core-shell (γ-FeOx@AuNP)@[C60(>DPAF-C9)](n)2 nanoparticles (NPs) in frequencies of 0.5-4.0 GHz. The detected relative dielectric constant amplification was initiated upon switching off the light followed by relaxation to give an excellent recyclability. These NPs having e(-)-polarizable fullerosomic structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@AuNPs. Surface-stabilized 2 in a core-shell structure was found to be capable of photoinducing the surface plasmonic resonance (SPR) effect by white LED light. The accumulated SPR energy was subsequently transferred to the partially bilayered C60(>DPAF-C9) fullerosomic membrane layer in a near-field (∼1.5 nm) region without producing radiation heat. Since the monostatic SAR signal is dielectric property-dependent, we used these measurements to provide evidence of derived reflectivity changes on a surface coated with 2 at 0.5-4.0 GHz upon illumination of LED white light. We found that a high, >99%, efficiency of response amplification in image amplitude can be achieved.

Interface plasmonic properties of silver coated by ultrathin metal oxides

NASA Astrophysics Data System (ADS)

Sytchkova, A.; Zola, D.; Grilli, M. L.; Piegari, A.; Fang, M.; He, H.; Shao, J.

2011-09-01

Many fields of high technology take advantage of conductor-dielectric interface properties. Deeper knowledge of physical processes that determine the optical response of the structures containing metal-dielectric interfaces is important for improving the performance of thin film devices containing such materials. Here we present a study on optical properties of several ultrathin metal oxides deposited over thin silver layers. Some widely used materials (Al2O3, SiO2, Y2O3, HfO2) were selected for deposition by r.f. sputtering, and the created metal-dielectric structures with two of them, alumina and silica, were investigated in this work using attenuated total reflectance (ATR) technique and by variable-angle spectroscopic ellipsometry (VASE). VASE was performed with a help of a commercial ellipsometer at various incident angles and in a wide spectral range. A home-made sample holder manufactured for WVASE ellipsometer and operational in Otto configuration has been implemented for angle-resolved and spectral ATR measurements. Simultaneous analysis of data obtained by these two independent techniques allows elaboration of a representative model for plasmonic-related phenomena at metal-dielectric interface. The optical constants of the interface layers formed between metal and ultrathin oxide layers are investigated. A series of oxides chosen for this study allows a comparative analysis aimed for selection of the most appropriate materials for different applications.

Electronic and optical properties of RESn{sub 3} (RE=Pr & Nd) intermetallics: A first principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pagare, G., E-mail: gita-pagare@yahoo.co.in; Abraham, Jisha A.; Department of Physics, National Defence Academy, Pune-411023

2015-06-24

A theoretical study of structural, electronic and optical properties of RESn{sub 3} (RE = Pr & Nd) intermetallics have been investigated systematically using first principles density functional theory. The calculations are carried out within the PBE-GGA and LSDA for the exchange correlation potential. The ground state properties such as lattice parameter (a{sub 0}), bulk modulus (B) and its pressure derivative (B′) are calculated and the calculated lattice parameters show well agreement with the experimental results. We first time predict elastic constants for these compounds. From energy dispersion curves, it is found that these compounds are metallic in nature. The linearmore » optical response of these compounds are also studied and the higher value of static dielectric constant shows the possibility to use them as good dielectric materials.« less

Probing the dielectric response of the interfacial buffer layer in epitaxial graphene via optical spectroscopy

NASA Astrophysics Data System (ADS)

Hill, Heather M.; Rigosi, Albert F.; Chowdhury, Sugata; Yang, Yanfei; Nguyen, Nhan V.; Tavazza, Francesca; Elmquist, Randolph E.; Newell, David B.; Hight Walker, Angela R.

2017-11-01

Monolayer epitaxial graphene (EG) is a suitable candidate for a variety of electronic applications. One advantage of EG growth on the Si face of SiC is that it develops as a single crystal, as does the layer below, referred to as the interfacial buffer layer (IBL), whose properties include an electronic band gap. Although much research has been conducted to learn about the electrical properties of the IBL, not nearly as much work has been reported on the optical properties of the IBL. In this work, we combine measurements from Mueller matrix ellipsometry, differential reflectance contrast, atomic force microscopy, and Raman spectroscopy, as well as calculations from Kramers-Kronig analyses and density-functional theory, to determine the dielectric function of the IBL within the energy range of 1 eV to 8.5 eV.

Intrinsic and extrinsic relaxation of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics: Effect of sintering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, J. Y.; Zhao, X. T.; Li, S. T.

2010-11-15

The effect of sintering process on the electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramic dielectrics were investigated in this paper. It was found that grain size is affected by sintering and the nonlinear current-voltage (I-V) property will decrease with the increased sintering time. Also, the frequency and temperature dependences of dielectric permittivity and loss in the ranges of 10{sup -1}-10{sup 7} Hz and 130-270 K were studied. Two relaxation processes with activation energy of 0.51 eV and 0.10 eV, respectively, were found in the frequency dependence of tan {delta} and Cole-Cole planes, which can be interpreted in termsmore » of insulating grain boundaries and semiconducting grains. It was suggested that grain boundary Maxwell-Wagner relaxation and ionization of oxygen vacancy V{sub O}{sup ++}, proposed as extrinsic and intrinsic relaxations, are responsible for the dielectric behaviors of CCTO ceramics.« less

Ultrawideband temperature-dependent dielectric properties of animal liver tissue in the microwave frequency range.

PubMed

Lazebnik, Mariya; Converse, Mark C; Booske, John H; Hagness, Susan C

2006-04-07

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.

Dielectric Spectroscopy in Biomaterials: Agrophysics

PubMed Central

El Khaled, Dalia; Castellano, Nuria N.; Gázquez, Jose A.; Perea-Moreno, Alberto-Jesus; Manzano-Agugliaro, Francisco

2016-01-01

Being dependent on temperature and frequency, dielectric properties are related to various types of food. Predicting multiple physical characteristics of agri-food products has been the main objective of non-destructive assessment possibilities executed in many studies on horticultural products and food materials. This review manipulates the basic fundamentals of dielectric properties with their concepts and principles. The different factors affecting the behavior of dielectric properties have been dissected, and applications executed on different products seeking the characterization of a diversity of chemical and physical properties are all pointed out and referenced with their conclusions. Throughout the review, a detailed description of the various adopted measurement techniques and the mostly popular equipment are presented. This compiled review serves in coming out with an updated reference for the dielectric properties of spectroscopy that are applied in the agrophysics field. PMID:28773438

Effect of doping ions on the structural defect and the electrical behavior of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Renzhong; Department of Technology and Physics, Zhengzhou University of Light Industry, Zhengzhou 450002; Zhao, Gaoyang, E-mail: zhaogy@xaut.edu.cn

Graphical abstract: The dielectric constant decreases with Ta doping, increases with Y doping and keeps almost constant with Zr doping compared with that of pure CCTO. - Highlights: • Y and Ta doping cause different defect types and concentration. • Defect influences the grain boundary mobility and results in different grain size. • Y doping increases the dielectric constant and decreases the nonlinear property. • Ta doping decreases the dielectric constant and enhances the nonlinear property. • Zr doped sample has nearly the defect type and dielectric properties as CaCu{sub 3}Ti{sub 4}O{sub 12}. - Abstract: The microstructure, dielectric and electricalmore » properties of CaCu{sub 3}Ti{sub 4−x}R{sub x}O{sub 12} (R = Y, Zr, Ta; x = 0 and 0.005) ceramics were investigated by XRD, Raman spectra, SEM and dielectric spectrum measurements. Positron annihilation measurements have been performed to investigate the influence of doping on the defects. The results show that all samples form a single crystalline phase. Y and Ta doping cause different defect types and increase the defect size and concentration, which influence the mobility of grain boundary and result in the different grain size. Y doping increases the dielectric constant and decreases the nonlinear property while Ta doping lead to an inverse result. Zr-doped sample has nearly the defect type, grain morphology and dielectric properties as pure CaCu{sub 3}Ti{sub 4}O{sub 12}. The effects of microstructure including the grain morphology and the vacancy defects on the mechanism of the dielectric and electric properties by doping are discussed.« less

A dielectric logging tool with insulated collar for formation fluid detection around borehole

NASA Astrophysics Data System (ADS)

Wang, Bin; Li, Kang; Kong, Fan-Min; Zhao, Jia

2015-08-01

A dielectric tool with insulated collar for analyzing fluid saturation outside a borehole was introduced. The UWB (ultra-wideband) antenna mounted on the tool was optimized to launch a transient pulse. The broadband evaluation method provided more advantages when compared with traditional dielectric tools. The EM (electromagnetic) power distribution outside the borehole was studied, and it was shown that energy was propagated in two modes. Furthermore, the mechanism of the modes was discussed. In order to increase this tools' investigation depth, a novel insulated collar was introduced. In addition, operation in difference formations was discussed and this tool proved to be able to efficiently launch lateral EM waves. Response voltages indicated that the proposed scheme was able to evaluate the fluid saturation of reservoir formations and dielectric dispersion properties. It may be used as an alternative tool for imaging logging applications.

Temperature-dependent ac conductivity and dielectric response of vanadium doped CaCu3Ti4O12 ceramic

NASA Astrophysics Data System (ADS)

Sen, A.; Maiti, U. N.; Thapa, R.; Chattopadhyay, K. K.

2011-09-01

Successful incorporation of vanadium dopant within the giant dielectric material CaCu 3Ti 4O12 (CCTO) through a conventional solid-state sintering process is achieved and its influence on the dielectric as well as electrical properties as a function of temperature and frequency is reported here. Proper crystalline phase formation together with dopant induced lattice constant shrinkage was confirmed through X-ray diffraction. The temperature dependence of the dielectric constant at different constant frequencies was investigated. We infer that the correlated barrier hopping (CBH) model is dominant in the conduction mechanism of the ceramic as per the temperature-dependent ac conductivity measurements. The electronic parameters such as density of the states at the Fermi level, N( E f) and hopping distance, R ω of the ceramic were also calculated using this model.

Lead halide perovskites: Crystal-liquid duality, phonon glass electron crystals, and large polaron formation

PubMed Central

Miyata, Kiyoshi; Atallah, Timothy L.; Zhu, X.-Y.

2017-01-01

Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices. These materials are characterized by coherent band transport expected from crystalline semiconductors, but dielectric responses and phonon dynamics typical of liquids. This “crystal-liquid” duality implies that lead halide perovskites belong to phonon glass electron crystals, a class of materials believed to make the most efficient thermoelectrics. We show that the crystal-liquid duality and the resulting dielectric response are responsible for large polaron formation and screening of charge carriers, leading to defect tolerance, moderate charge carrier mobility, and radiative recombination properties. Large polaron formation, along with the phonon glass character, may also explain the marked reduction in hot carrier cooling rates in these materials. PMID:29043296

Dielectric properties of Ni-coated BaTiO/sub 3-/PMMA composite.

PubMed

Park, Jung Min; Lee, Hee Young; Kim, Jeong-Joo; Park, Eun Tae; Chung, Yul-Kyo

2008-05-01

Dielectric properties of Ni-coated BaTiO(3)-PMMA (polymethyl methacrylate) composite were studied from an embedded capacitor application viewpoint. Volume loading of up to 50% was attempted, and the results were compared with uncoated BaTiO(3)-PMMA composite. Ni-coating on BaTiO(3) powder was found to greatly improve the dielectric properties of the composite, especially the dielectric constant value. K values of about 100 with temperature-stable X7E characteristics were realized.

Current understanding of structure-processing-property relationships in BaTiO 3-Bi( M)O 3 dielectrics

DOE PAGES

Beuerlein, Michaela A.; Kumar, Nitish; Usher, Tedi -Marie; ...

2016-09-01

Here, as part of a continued push for high permittivity dielectrics suitable for use at elevated operating temperatures and/or large electric fields, modifications of BaTiO 3 with Bi( M)O 3, where M represents a net-trivalent B-site occupied by one or more species, have received a great deal of recent attention. Materials in this composition family exhibit weakly coupled relaxor behavior that is not only remarkably stable at high temperatures and under large electric fields, but is also quite similar across various identities of M. Moderate levels of Bi content (as much as 50 mol%) appear to be crucial to themore » stability of the dielectric response. In addition, the presence of significant Bi reduces the processing temperatures required for densification and increases the required oxygen content in processing atmospheres relative to traditional X7R-type BaTiO 3-based dielectrics. Although detailed understanding of the structure–processing–property relationships in this class of materials is still in its infancy, this article reviews the current state of understanding of the mechanisms underlying the high and stable values of both relative permittivity and resistivity that are characteristic of BaTiO 3-Bi( M)O 3 dielectrics as well as the processing challenges and opportunities associated with these materials.« less

FAST TRACK COMMUNICATION: Ferroelectric properties and dielectric responses of multiferroic BiFeO3 films grown by RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Qi, Xiaoding; Tsai, Po-Chou; Chen, Yi-Chun; Ko, Cheng-Hung; Huang, Jung-Chun-Andrew; Chen, In-Gann

2008-12-01

Multiferroic BiFeO3 films have been grown on LaNiO3-x/SrTiO3 and Pt/Si substrates by RF magnetron sputtering. The films showed fully saturated ferroelectric hysteresis loops with large remanent polarization of 64 µC cm-2, suitable for most device applications. Piezoresponse force microscopy confirmed that the films were electrically writable. In addition to the high-frequency intrinsic dielectric loss of epitaxial films, the Argand diagram also revealed low-frequency contributions from both dc conductivity and interfacial polarization at electrodes. For polycrystalline films on Pt/Si, the dominant contribution to dielectric loss was space charge polarization at grain boundaries.

Influence of Ag substitution on structural and dielectric properties of TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Ali, T.; Ahmed, Ateeq; Siddique, M. Naseem; Aftab, Tabish; Tripathi, P.

2018-04-01

In this paper, we report the structural, electrical and dielectric properties of Ag-substituted TiO2 nanoparticles synthesized by sol-gel method. The X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles are pure and crystalline in nature and showing tetragonal anatase phase of TiO2. TEM micrograph shows that shapes of the nanoparticles are non-spherical. We have also studied the dielectric properties and in relation to it the dielectric constants, dielectric loss and A.C. conductivity have been studied as the function of frequency and composition of iron. The above theory may be explained by `Maxwell Wagner Model'.

Submillimeter and Far-Infrared Dielectric Properties of Thin Films

NASA Technical Reports Server (NTRS)

Cataldo, Giuseppe; Wollack, Edward J.

2016-01-01

The complex dielectric function enables the study of a material's refractive and absorptive properties and provides information on a material's potential for practical application. Commonly employed line shape profile functions from the literature are briefly surveyed and their suitability for representation of dielectric material properties are discussed. An analysis approach to derive a material's complex dielectric function from observed transmittance spectra in the far-infrared and submillimeter regimes is presented. The underlying model employed satisfies the requirements set by the Kramers-Kronig relations. The dielectric function parameters derived from this approach typically reproduce the observed transmittance spectra with an accuracy of less than 4%.

Metal clusters and nanoparticles in dielectric matrices: Formation and optical properties

NASA Astrophysics Data System (ADS)

Gladskikh, I. A.; Vartanyan, T. A.

2016-12-01

The optical properties of thin dielectric films with metal inclusions and their dependence on thermal and laser annealing are studied experimentally. Metal clusters (Ag, Au, and Cu) in dielectric materials (Al2O3 and SiO2) are obtained by simultaneous vacuum deposition of metal and dielectric on the surface of a corresponding dielectric substrate (sapphire and quartz). It is shown that, depending on the deposited dielectric material, on the weight ratio of deposited metal and dielectric, and on the subsequent thermal treatment, one can obtain different metal structures, from clusters with a small number of atoms to complex dendritic plasmonic structures.

Microwave measurement and modeling of the dielectric properties of vegetation

NASA Astrophysics Data System (ADS)

Shrestha, Bijay Lal

Some of the important applications of microwaves in the industrial, scientific and medical sectors include processing and treatment of various materials, and determining their physical properties. The dielectric properties of the materials of interest are paramount irrespective of the applications, hence, a wide range of materials covering food products, building materials, ores and fuels, and biological materials have been investigated for their dielectric properties. However, very few studies have been conducted towards the measurement of dielectric properties of green vegetations, including commercially important plant crops such as alfalfa. Because of its high nutritional value, there is a huge demand for this plant and its processed products in national and international markets, and an investigation into the possibility of applying microwaves to improve both the net yield and quality of the crop can be beneficial. Therefore, a dielectric measurement system based upon the probe reflection technique has been set up to measure dielectric properties of green plants over a frequency range from 300 MHz to 18 GHz, moisture contents from 12%, wet basis to 79%, wet basis, and temperatures from -15°C to 30°C. Dielectric properties of chopped alfalfa were measured with this system over frequency range of 300 MHz to 18 GHz, moisture content from 11.5%, wet basis, to 73%, wet basis, and density over the range from 139 kg m-3 to 716 kg m-3 at 23°C. The system accuracy was found to be +/-6% and +/-10% in measuring the dielectric constant and loss factor respectively. Empirical, semi empirical and theoretical models that require only moisture content and operating frequency were determined to represent the dielectric properties of both leaves and stems of alfalfa at 22°C. The empirical models fitted the measured dielectric data extremely well. The root mean square error (RMSE) and the coefficient of determination (r2) for dielectric constant and loss factor of leaves were 0.89 and 0.99, and 0.52 and 0.99 respectively. The RMSE and r2 values for dielectric constant and loss factor of stems were 0.89 and 0.99, and 0.77 and 0.99 respectively. Among semi empirical or theoretical models, Power law model showed better performance (RMSE = 1.78, r2 = 0.96) in modeling dielectric constant of leaves, and Debye-ColeCole model was more appropriate (RMSE = 1.23, r2 = 0.95) for the loss factor. For stems, the Debye-ColeCole models (developed on an assumption that they do not shrink as they dry) were found to be the best models to calculate the dielectric constant with RMSE 0.53 and r2 = 0.99, and dielectric loss factor with RMSE = 065 and r2 = 0.95. (Abstract shortened by UMI.)

Open-Ended Coaxial Probe Technique for Dielectric Measurement of Biological Tissues: Challenges and Common Practices.

PubMed

La Gioia, Alessandra; Porter, Emily; Merunka, Ilja; Shahzad, Atif; Salahuddin, Saqib; Jones, Marggie; O'Halloran, Martin

2018-06-05

Electromagnetic (EM) medical technologies are rapidly expanding worldwide for both diagnostics and therapeutics. As these technologies are low-cost and minimally invasive, they have been the focus of significant research efforts in recent years. Such technologies are often based on the assumption that there is a contrast in the dielectric properties of different tissue types or that the properties of particular tissues fall within a defined range. Thus, accurate knowledge of the dielectric properties of biological tissues is fundamental to EM medical technologies. Over the past decades, numerous studies were conducted to expand the dielectric repository of biological tissues. However, dielectric data is not yet available for every tissue type and at every temperature and frequency. For this reason, dielectric measurements may be performed by researchers who are not specialists in the acquisition of tissue dielectric properties. To this end, this paper reviews the tissue dielectric measurement process performed with an open-ended coaxial probe. Given the high number of factors, including equipment- and tissue-related confounders, that can increase the measurement uncertainty or introduce errors into the tissue dielectric data, this work discusses each step of the coaxial probe measurement procedure, highlighting common practices, challenges, and techniques for controlling and compensating for confounders.

Electrocaloric Refrigeration for Superconductors

DTIC Science & Technology

1977-02-01

Dielectric properties 40 3.3.2. Relation to capacitance thermometer manufacturing . . 42 3.4. SrTiO, Glass-Ceramic Multilayer Samples 42 3.4.1...Experimental Methods 66 3.6.1. Dielectric properties 66 3.6.2. Thermodynamic properties 7 0 3.6.3. Thermal conductivity. .... 80 3.7...Discussion of Experimental Results 143 3.8.1. Dielectric Troperties 143 3.8.2. Thermal Properties 150 3.8.3. Recommendations for further work

Research Update: Polyimide/CaCu3Ti4O12 nanofiber functional hybrid films with improved dielectric properties

NASA Astrophysics Data System (ADS)

Yang, Yang; Wang, Ziyu; Ding, Yi; Lu, Zhihong; Sun, Haoliang; Li, Ya; Wei, Jianhong; Xiong, Rui; Shi, Jing; Liu, Zhengyou; Lei, Qingquan

2013-11-01

This work reports the excellent dielectric properties of polyimide (PI) embedded with CaCu3Ti4O12 (CCTO) nanofibers. The dielectric behaviors were investigated over a frequency of 100 Hz-1 MHz. It is shown that embedding CCTO nanofibers with high aspect ratio (67) is an effective means to enhance the dielectric permittivity and reduce the percolation threshold. The dielectric permittivity of PI/CCTO nanofiber composites is 85 with 1.5 vol.% loading of filler, also the dielectric loss is only 0.015 at 100 Hz. Monte Carlo simulation was used to investigate the percolation threshold of CCTO nanofibers reinforced polyimide matrix by using excluded volume theory and soft, hard-core models. The results are in good agreement with the percolation theory and the hard-core model can well explain the percolation phenomena in PI/CCTO nanofiber composites. The dielectric properties of the composites will meet the practical requirements for the application in high dielectric constant capacitors and high energy density materials.

Nonthermal combined ultraviolet and vacuum-ultraviolet curing process for organosilicate dielectrics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, H.; Guo, X.; Pei, D.

2016-06-13

Porous SiCOH films are of great interest in semiconductor fabrication due to their low-dielectric constant properties. Post-deposition treatments using ultraviolet (UV) light on organosilicate thin films are required to decompose labile pore generators (porogens) and to ensure optimum network formation to improve the electrical and mechanical properties of low-k dielectrics. The goal of this work is to choose the best vacuum-ultraviolet photon energy in conjunction with vacuum ultraviolet (VUV) photons without the need for heating the dielectric to identify those wavelengths that will have the most beneficial effect on improving the dielectric properties and minimizing damage. VUV irradiation between 8.3more » and 8.9 eV was found to increase the hardness and elastic modulus of low-k dielectrics at room temperature. Combined with UV exposures of 6.2 eV, it was found that this “UV/VUV curing” process is improved compared with current UV curing. We show that UV/VUV curing can overcome drawbacks of UV curing and improve the properties of dielectrics more efficiently without the need for high-temperature heating of the dielectric.« less

New calibration algorithms for dielectric-based microwave moisture sensors

USDA-ARS?s Scientific Manuscript database

New calibration algorithms for determining moisture content in granular and particulate materials from measurement of the dielectric properties at a single microwave frequency are proposed. The algorithms are based on identifying empirically correlations between the dielectric properties and the par...

A Study of Dielectric Properties of Proteinuria between 0.2 GHz and 50 GHz

PubMed Central

Mun, Peck Shen; Ting, Hua Nong; Ong, Teng Aik; Wong, Chew Ming; Ng, Kwan Hong; Chong, Yip Boon

2015-01-01

This paper investigates the dielectric properties of urine in normal subjects and subjects with chronic kidney disease (CKD) at microwave frequency of between 0.2 GHz and 50 GHz. The measurements were conducted using an open-ended coaxial probe at room temperature (25°C), at 30°C and at human body temperature (37°C). There were statistically significant differences in the dielectric properties of the CKD subjects compared to those of the normal subjects. Statistically significant differences in dielectric properties were observed across the temperatures for normal subjects and CKD subjects. Pearson correlation test showed the significant correlation between proteinuria and dielectric properties. The experimental data closely matched the single-pole Debye model. The relaxation dispersion and relaxation time increased with the proteinuria level, while decreasing with the temperature. As for static conductivity, it increased with proteinuria level and temperature. PMID:26066351

Changes in the dielectric properties of rat tissue as a function of age at microwave frequencies

NASA Astrophysics Data System (ADS)

Peyman, A.; Rezazadeh, A. A.; Gabriel, C.

2001-06-01

The dielectric properties of ten rat tissues at six different ages were measured at 37 °C in the frequency range of 130 MHz to 10 GHz using an open-ended coaxial probe and a computer controlled network analyser. The results show a general decrease of the dielectric properties with age. The trend is more apparent for brain, skull and skin tissues and less noticeable for abdominal tissues. The variation in the dielectric properties with age is due to the changes in the water content and the organic composition of tissues. The percentage decrease in the dielectric properties of certain tissues in the 30 to 70 day old rats at cellular phone frequencies have been tabulated. These data provide an important input in the provision of rigorous dosimetry in lifetime-exposure animal experiments. The results provide some insight into possible differences in the assessment of exposure for children and adults.

The review of various synthesis methods of barium titanate with the enhanced dielectric properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

More, S. P., E-mail: smitalomte@gmail.com; Topare, R. J., E-mail: r-topare@yahoo.com

2016-05-06

The Barium Titanate is a very well known dielectric ceramic belongs to perovskite structure. It has very wide applications in the field of electronic, electro ceramic, electromechanical and electro-optical applications. Barium Titanate has very high dielectric constant as well as low dielectric loss. Substituted dielectrics are one of the most important technological compounds in modern electro ceramics. Its electrical properties can be tuned flexibly by a simple substitution technique. This has encouraged researchers to select a typical cation to be substituted at cationic sites. In the present paper, the review of various synthesis methods of Barium Titanate compound with themore » effect of different dopants, the grain size on the dielectric properties at various temperatures is discussed.« less

Study by molecular dynamics of the influence of temperature and pressure on the optical properties of undoped 3C-SiC structures

NASA Astrophysics Data System (ADS)

Domingues, Gilberto; Monthe, Aubin Mekeze; Guévelou, Simon; Rousseau, Benoit

2018-01-01

Silicon carbide (SiC)-based open-cell foams appear to be promising porous materials for designing high-temperature energy conversion systems such as volumetric solar receivers. In these media, heat transfers and fluid flows occur simultaneously. The numerical models developed for computing the thermal efficiencies of SiC foams must take into account the energy contribution of thermal radiation. In particular, the thermal radiative properties of these foams must be accurately known. This explains why knowledge of the pressure and temperature dependences of the optical properties of the crystalline parts, which compose the foams, is of primary concern for computing the latter properties correctly. However, the data available in the literature provide the evolution laws of the dielectric functions, needed to calculate the optical properties, as dependent on one thermodynamic parameter at a time. To deal with this issue, a study of the temperature/pressure influence on the dielectric functions of a silicon carbide structure by simulation with molecular dynamics (MD) is presented in this paper. The Vashishta interaction potential, based on the sum of two- and three-body terms, is used in this study. The simulations are carried out on undoped 3C-SiC at pressures ranging from 0.2 to 20 GPa and temperatures ranging from 300 K to 1500 K. The dielectric functions are obtained by applying the linear response theory and comparing them with values provided in the literature, using a Lorentz model. The simulated results, in good agreement with the experimental ones, make it possible to establish the evolution laws of the dielectric functions with both parameters, temperature and pressure, applicable to any field requiring the use of undoped silicon carbide.

Enhanced dielectric and piezoelectric responses in Zn 1 -xMg xO thin films near the phase separation boundary

DOE PAGES

Kang, Xiaoyu; Shetty, Smitha; Garten, Lauren; ...

2017-01-23

Dielectric and piezoelectric properties for Zn 1-xMg xO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn 1-xMg xO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane ( d33,f) and in-plane ( e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectricmore » coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. As a result, the enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn 1-xMg xO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.« less

Dielectric Properties of Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC)-CaCu3Ti4O12 (CCTO) Composite

NASA Astrophysics Data System (ADS)

Mallmann, E. J. J.; Silva, M. A. S.; Sombra, A. S. B.; Botelho, M. A.; Mazzetto, S. E.; de Menezes, A. S.; Almeida, A. F. L.; Fechine, P. B. A.

2015-01-01

The main object of this work is to study two materials with giant dielectric constants: CaCu3Ti4O12 (CCTO) and Ca0.7Bi0.3Ti0.7Cr0.3O3 (CBTC). CBTC1- x -CCTO x composites were also obtained to create a new dielectric material with dielectric properties between these two phases. Structural properties were studied by x-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy and dielectric measurements. CCTO showed a cubic phase and CBTC an orthorhombic phase. An interesting result was that the dielectric constant ( K) did not follow the rule of the mixture of Lichtnecker, and this happened due to the presence of other phases of its crystalline structure, which decreases the value of K when compared to the predicted values of Lichtnecker. It was also found that the dielectric properties of the composite are very promising for use in microelectronics, according to the miniaturization factor, which is crucial for those applications.

Characterization of polybenzimidazole (PBI) film at high temperatures

NASA Astrophysics Data System (ADS)

Hammoud, Ahmad N.; Suthar, J. L.

1992-04-01

Polybenzimidazole, a linear thermoplastic polymer with excellent thermal stability and strength retention over a wide range of temperatures, was evaluated for its potential use as the main dielectric in high temperature capacitors. The film was characterized in terms of its dielectric properties in a frequency range of 50 Hz to 100 kilo-Hz. These properties, which include the dielectric constant and dielectric loss, were also obtained in a temperature range from 20 C to 300 C with an electrical stress of 60 Hz, 50 V/mil present. The alternating and direct current breakdown voltages of silicone oil impregnated films as a function of temperature were also determined. The results obtained indicate that while the film remained relatively stable up to 200 C, it exhibited an increase in its dielectric properties as the temperature was raised to 300 C. It was also found that conditioning of the film by heat treatment at 60 C for six hours tended to improve its dielectric and breakdown properties. The results are discussed and conclusions made concerning the suitability of the film as a high temperature capacitor dielectric.

Characterization of polybenzimidazole (PBI) film at high temperatures

NASA Technical Reports Server (NTRS)

Hammoud, Ahmad N.; Suthar, J. L.

1992-01-01

Polybenzimidazole, a linear thermoplastic polymer with excellent thermal stability and strength retention over a wide range of temperatures, was evaluated for its potential use as the main dielectric in high temperature capacitors. The film was characterized in terms of its dielectric properties in a frequency range of 50 Hz to 100 kilo-Hz. These properties, which include the dielectric constant and dielectric loss, were also obtained in a temperature range from 20 C to 300 C with an electrical stress of 60 Hz, 50 V/mil present. The alternating and direct current breakdown voltages of silicone oil impregnated films as a function of temperature were also determined. The results obtained indicate that while the film remained relatively stable up to 200 C, it exhibited an increase in its dielectric properties as the temperature was raised to 300 C. It was also found that conditioning of the film by heat treatment at 60 C for six hours tended to improve its dielectric and breakdown properties. The results are discussed and conclusions made concerning the suitability of the film as a high temperature capacitor dielectric.

Characterization of the effective electrostriction coefficients in ferroelectric thin films

NASA Astrophysics Data System (ADS)

Kholkin, A. L.; Akdogan, E. K.; Safari, A.; Chauvy, P.-F.; Setter, N.

2001-06-01

Electromechanical properties of a number of ferroelectric films including PbZrxTi1-xO3(PZT), 0.9PbMg1/3Nb2/3O3-0.1PbTiO3(PMN-PT), and SrBi2Ta2O9(SBT) are investigated using laser interferometry combined with conventional dielectric measurements. Effective electrostriction coefficients of the films, Qeff, are determined using a linearized electrostriction equation that couples longitudinal piezoelectric coefficient, d33, with the polarization and dielectric constant. It is shown that, in PZT films, electrostriction coefficients slightly increase with applied electric field, reflecting the weak contribution of non-180° domains to piezoelectric properties. In contrast, in PMN-PT and SBT films electrostriction coefficients are field independent, indicating the intrinsic nature of the piezoelectric response. The experimental values of Qeff are significantly smaller than those of corresponding bulk materials due to substrate clamping and possible size effects. Electrostriction coefficients of PZT layers are shown to depend strongly on the composition and preferred orientation of the grains. In particular, Qeff of (100) textured rhombohedral films (x=0.7) is significantly greater than that of (111) layers. Thus large anisotropy of the electrostrictive coefficients is responsible for recently observed large piezoelectric coefficients of (100) textured PZT films. Effective electrostriction coefficients obtained by laser interferometry allow evaluation of the electromechanical properties of ferroelectric films based solely on the dielectric parameters and thus are very useful in the design and fabrication of microsensors and microactuators.

Thermal remote sensing: theory, sensors, and applications

USDA-ARS?s Scientific Manuscript database

Applications of thermal infrared remote sensing for Earth science research are both varied and wide in scope. They range from understanding thermal energy responses that drive land-atmosphere energy exchanges in the hydrologic cycle, to measurement of dielectric surface properties for snow, ice, an...

Effect of crystal orientation on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Huaping, E-mail: wuhuaping@gmail.com, E-mail: hpwu@zjut.edu.cn; State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024; Ma, Xuefu

2016-01-15

The influence of crystal orientations on the phase diagrams, dielectric and piezoelectric properties of epitaxial BaTiO{sub 3} thin films has been investigated using an expanded nonlinear thermodynamic theory. The calculations reveal that crystal orientation has significant influence on the phase stability and phase transitions in the misfit strain-temperature phase diagrams. In particular, the (110) orientation leads to a lower symmetry and more complicated phase transition than the (111) orientation in BaTiO{sub 3} films. The increase of compressive strain will dramatically enhance the Curie temperature T{sub C} of (110)-oriented BaTiO{sub 3} films, which matches well with previous experimental data. The polarizationmore » components experience a great change across the boundaries of different phases at room temperature in both (110)- and (111)-oriented films, which leads to the huge dielectric and piezoelectric responses. A good agreement is found between the present thermodynamics calculation and previous first-principles calculations. Our work provides an insight into how to use crystal orientation, epitaxial strain and temperature to tune the structure and properties of ferroelectrics.« less

Electrical properties of AC{sub 3}B{sub 4}O{sub 12}-type perovskite ceramics with different cation vacancies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Guizhong; Chen, Zhi; Sun, Xiaojun

2015-05-15

Highlights: • AC{sub 3}B{sub 4}O{sub 12} perovskite with different concentration cation vacancies were prepared. • Cell parameter decreases with the increase of concentration of cation vacancies. • PTCO and CTO remain high dielectric permittivity but depress loss greatly. • Dielectric loss associates with cation vacancies and motion of oxygen vacancies. - Abstract: AC{sub 3}B{sub 4}O{sub 12}-type perovskite CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO), □{sub 0.34}Pr{sub 0.67}Cu{sub 3}Ti{sub 4}O{sub 12} (PCTO), □{sub 1}Cu{sub 3}Ta{sub 2}Ti{sub 2}O{sub 12} (CTTO), □{sub 2}Cu{sub 2}Ta{sub 4}O{sub 12} (CTO) ceramics with different concentration cation vacancies were prepared through traditional solid state reaction method. X-ray diffraction analysis indicatedmore » that CCTO and PCTO are perovskite cubic with space group Im-3 (no. 204) while CTTO and CTO are Pm-3 (no. 200). Cell parameter of the samples dramatically increases with the increase of cation vacancies. Dielectric permittivity of them maintains very high value of ∼10{sup 4} from room temperature to 550 K but the dielectric loss is depressed with the increase of cation vacancies in the same space group. The dielectric properties and conductivity behavior were described by the Debye relaxation and the universal dielectric response, respectively. The effect mechanism of cation vacancy and crystal structure on carrier transposition were discussed.« less

Investigation of dielectric properties of polymer composites reinforced with carbon nanotubes in the frequency band of 0.01 Hz - 10 MHz

NASA Astrophysics Data System (ADS)

Goshev, A. A.; Eseev, M. K.; Kapustin, S. N.; Vinnik, L. N.; Volkov, A. S.

2016-08-01

The goal of this work is experimental study of dielectric properties of polymer nanocomposites reinforced with multiwalled carbon nanotubes (MWCNTs) in alternating electric field in low frequency band of 0.01 Hz - 10 MHz. We investigated the influence, functionalization degree, aspect ratio, concentration of carbon nanotubes (CNTs) on dielectric properties of polymer sample. We also studied the dependence of dielectric properties on the polymerization temperature. The dependence of CNTs agglomeration on sample polymerization temperature and temperature's influence on conductivity has been shown. We conducted model calculation of percolation threshold and figured out its dependence on CNTs aspect ratio.

Depolarization current relaxation process of insulating dielectrics after corona poling under different charging conditions

NASA Astrophysics Data System (ADS)

Zhang, J. W.; Zhou, T. C.; Wang, J. X.; Yang, X. F.; Zhu, F.; Tian, L. M.; Liu, R. T.

2017-10-01

As an insulating dielectric, polyimide is favorable for the application of optoelectronics, electrical insulation system in electric power industry, insulating, and packaging materials in space aircraft, due to its excellent thermal, mechanical and electrical insulating stability. The charge storage profile of such insulating dielectric is utmost important to its application, when it is exposed to electron irradiation, high voltage corona discharge or other treatments. These treatments could induce changes in physical and chemical properties of treated samples. To investigate the charge storage mechanism of the insulating dielectrics after high-voltage corona discharge, the relaxation processes responsible for corona charged polyimide films under different poling conditions were analyzed by the Thermally Stimulated Discharge Currents method (TSDC). In the results of thermal relaxation process, the appearance of various peaks in TSDC spectra provided a deep insight into the molecular status in the dielectric material and reflected stored space charge relaxation process in the insulating polymers after corona discharge treatments. Furthermore, the different space charge distribution status under various poling temperature and different discharge voltage level were also investigated, which could partly reflect the influence of the ambiance condition on the functional dielectrics after corona poling.

Nonlinear Dynamical Model of a Soft Viscoelastic Dielectric Elastomer

NASA Astrophysics Data System (ADS)

Zhang, Junshi; Chen, Hualing; Li, Dichen

2017-12-01

Actuated by alternating stimulation, dielectric elastomers (DEs) show a behavior of complicated nonlinear vibration, implying a potential application as dynamic electromechanical actuators. As is well known, for a vibrational system, including the DE system, the dynamic properties are significantly affected by the geometrical sizes. In this article, a nonlinear dynamical model is deduced to investigate the geometrical effects on dynamic properties of viscoelastic DEs. The DEs with square and arbitrary rectangular geometries are considered, respectively. Besides, the effects of tensile forces on dynamic performances of rectangular DEs with comparably small and large geometrical sizes are explored. Phase paths and Poincaré maps are utilized to detect the periodicity of the nonlinear vibrations of DEs. The resonance characteristics of DEs incorporating geometrical effects are also investigated. The results indicate that the dynamic properties of DEs, including deformation response, vibrational periodicity, and resonance, are tuned when the geometrical sizes vary.

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

NASA Astrophysics Data System (ADS)

Krohns, S.; Lu, J.; Lunkenheimer, P.; Brizé, V.; Autret-Lambert, C.; Gervais, M.; Gervais, F.; Bourée, F.; Porcher, É. F.; Loidl, A.

2009-11-01

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and X-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T. At low temperatures the dielectric constant shows a minor but significant dependence on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.

Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite

PubMed Central

Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao

2015-01-01

The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 108 Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 108 Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913

Low-loss electromagnetic composites for RF and microwave applications.

PubMed

Wang, Hong; Yang, Haibo; Xiang, Feng; Yao, Xi

2011-09-01

Low-loss electromagnetic composites with high permittivity and permeability will benefit the miniaturization and multifunctional of RF devices. A kind of low-loss dielectric-magnetic ceramic-ceramic composite was developed by hybrid processing technology with the goal of integrating the dielectric properties and magnetic properties. The hybrid processing technology exhibits the advantage of lowered sintering temperatures for the composites while retaining good microstructure and high performance. By introducing elastomer as matrix, a kind of flexible low-loss dielectric-magnetic ceramic-polymer composite was prepared and studied. The obtained flexible dielectric-magnetic ceramic-polymer composite exhibited low loss and good mechanical properties. The results show good effects on lowering the dielectric loss and extending the cut-off magnetic frequency of the electromagnetic composite. Methods for tailoring the properties of the multifunctional composites were proposed and discussed.

Enhanced dielectric properties of Fe-substituted TiO2 nanoparticles

NASA Astrophysics Data System (ADS)

Ali, T.; Ahmed, Ateeq; Naseem siddique, M.; Tripathi, P.

2018-04-01

We report the structural and dielectric properties Ti1-xFexO2 (0.00 < x < 0.10) nanoparticles (NPs) synthesized by sol-gel method. The synthesized material has been characterized by soft X-ray absorption spectroscopy (SXAS) in order to investigate the fine structure and electronic valence state. SXAS analysis reveals that Fe-ions exist only in 3+ valance state in all the samples. The dielectric properties were studied by the use of LCR impedance spectroscopy. The dielectric constants, dielectric loss and A.C. conductivity have been determined as a function of frequency and composition of iron. At higher frequencies, the materials exhibited high AC Conductivity and low dielectric constant. The above theory could be explained by 'Maxwell Wagner Model' and may provide a new insight to fabricate nanomaterials having possible electrical application.

Microwave dielectric properties of boreal forest trees

NASA Technical Reports Server (NTRS)

Xu, G.; Ahern, F.; Brown, J.

1993-01-01

The knowledge of vegetation dielectric behavior is important in studying the scattering properties of the vegetation canopy and radar backscatter modelling. Until now, a limited number of studies have been published on the dielectric properties in the boreal forest context. This paper presents the results of the dielectric constant as a function of depth in the trunks of two common boreal forest species: black spruce and trembling aspen, obtained from field measurements. The microwave penetration depth for the two species is estimated at C, L, and P bands and used to derive the equivalent dielectric constant for the trunk as a whole. The backscatter modelling is carried out in the case of black spruce and the results are compared with the JPL AIRSAR data. The sensitivity of the backscatter coefficient to the dielectric constant is also examined.

Heat treatment effects on dielectric properties of SRFe{sub 12}O{sub 19} hexaferrite prepared by an SHS route

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panchal, Nital R.; Jotania, Rajshree B., E-mail: natal_panchal@yahoo.co.in, E-mail: rbjotania@gmail.com

2011-07-01

The M-type Strontium Hexaferrite SRFe{sub 12}O{sub 19} particles were prepared by a Self propagating High temperature Synthesis (SHS) route. Precursors were heated under two different conditions: microwave heating for 30 minutes and sintered at 950 deg C for 4 hrs. The dielectric properties: dielectric constant ({epsilon}{sup '}), dielectric loss (tan {delta} ) and ac conductivity ({sigma}{sub ac}) were measured at room temperature in the frequency range from 100 Hz to 2 MHz. The samples present a non-linear behavior for the dielectric constant at 1 kHz, 100 kHz and 2 MHz. The dielectric properties of prepared Strontium Hexaferrite samples were discussedmore » in view of applications as a material for microwave devices, permanent magnets and high density magnetic recording media. (author)« less

Dielectric properties of proteins from simulations: tools and techniques

NASA Astrophysics Data System (ADS)

Simonson, Thomas; Perahia, David

1995-09-01

Tools and techniques to analyze the dielectric properties of proteins are described. Microscopic dielectric properties are determined by a susceptibility tensor of order 3 n, where n is the number of protein atoms. For perturbing charges not too close to the protein, the dielectric relaxation free energy is directly related to the dipole-dipole correlation matrix of the unperturbed protein, or equivalently to the covariance matrix of its atomic displacements. These are straightforward to obtain from existing molecular dynamics packages such as CHARMM or X- PLOR. Macroscopic dielectric properties can be derived from the dipolar fluctuations of the protein, by idealizing the protein as one or more spherical media. The dipolar fluctuations are again directly related to the covariance matrix of the atomic displacements. An interesting consequence is that the quasiharmonic approximation, which by definition exactly reproduces this covariance matrix, gives the protein dielectric constant exactly. Finally a technique is reviewed to obtain normal or quasinormal modes of vibration of symmetric protein assemblies. Using elementary group theory, and eliminating the high-frequency modes of vibration of each monomer, the limiting step in terms of memory and computation is finding the normal modes of a single monomer, with the other monomers held fixed. This technique was used to study the dielectric properties of the Tobacco Mosaic Virus protein disk.

Atomistic determination of flexoelectric properties of crystalline dielectrics

NASA Astrophysics Data System (ADS)

Maranganti, R.; Sharma, P.

2009-08-01

Upon application of a uniform strain, internal sublattice shifts within the unit cell of a noncentrosymmetric dielectric crystal result in the appearance of a net dipole moment: a phenomenon well known as piezoelectricity. A macroscopic strain gradient on the other hand can induce polarization in dielectrics of any crystal structure, even those which possess a centrosymmetric lattice. This phenomenon, called flexoelectricity, has both bulk and surface contributions: the strength of the bulk contribution can be characterized by means of a material property tensor called the bulk flexoelectric tensor. Several recent studies suggest that strain-gradient induced polarization may be responsible for a variety of interesting and anomalous electromechanical phenomena in materials including electromechanical coupling effects in nonuniformly strained nanostructures, “dead layer” effects in nanocapacitor systems, and “giant” piezoelectricity in perovskite nanostructures among others. In this work, adopting a lattice dynamics based microscopic approach we provide estimates of the flexoelectric tensor for certain cubic crystalline ionic salts, perovskite dielectrics, III-V and II-VI semiconductors. We compare our estimates with experimental/theoretical values wherever available and also revisit the validity of an existing empirical scaling relationship for the magnitude of flexoelectric coefficients in terms of material parameters. It is interesting to note that two independent groups report values of flexoelectric properties for perovskite dielectrics that are orders of magnitude apart: Cross and co-workers from Penn State have carried out experimental studies on a variety of materials including barium titanate while Catalan and co-workers from Cambridge used theoretical ab initio techniques as well as experimental techniques to study paraelectric strontium titanate as well as ferroelectric barium titanate and lead titanate. We find that, in the case of perovskite dielectrics, our estimates agree to an order of magnitude with the experimental and theoretical estimates for strontium titanate. For barium titanate however, while our estimates agree to an order of magnitude with existing ab initio calculations, there exists a large discrepancy with experimental estimates. The possible reasons for the observed deviations are discussed.

Evidence for power-law frequency dependence of intrinsic dielectric response in the Ca Cu3 Ti4 O12

NASA Astrophysics Data System (ADS)

Tselev, Alexander; Brooks, Charles M.; Anlage, Steven M.; Zheng, Haimei; Salamanca-Riba, Lourdes; Ramesh, R.; Subramanian, M. A.

2004-10-01

We investigated the dielectric response of CaCu3Ti4O12 (CCTO) thin films grown epitaxially on LaAlO3 (001) substrates by pulsed laser deposition. The dielectric response of the films was found to be strongly dominated by a power law in frequency, typical of materials with localized hopping charge carriers, in contrast to the Debye-like response of the bulk material. The film conductivity decreases with annealing in oxygen, and it suggests that oxygen deficit is a cause of the relatively high film conductivity. With increase of the oxygen content, the room temperature frequency response of the CCTO thin films changes from the response indicating the presence of some relatively low conducting capacitive layers to purely power law, and then toward a frequency independent response with a relative dielectric constant ɛ'˜102 . The film conductance and dielectric response decrease upon decrease of the temperature, with dielectric response being dominated by the power-law frequency dependence. Below ˜80K , the dielectric response of the films is frequency independent with ɛ' close to 102 . The results provide another piece of evidence for an extrinsic, Maxwell-Wagner type, origin of the colossal dielectric response of the bulk CCTO material, connected with electrical inhomogeneity of the bulk material.

Nonlocality and particle-clustering effects on the optical response of composite materials with metallic nanoparticles

NASA Astrophysics Data System (ADS)

Chen, C. W.; Chung, H. Y.; Chiang, H.-P.; Lu, J. Y.; Chang, R.; Tsai, D. P.; Leung, P. T.

2010-10-01

The optical properties of composites with metallic nanoparticles are studied, taking into account the effects due to the nonlocal dielectric response of the metal and the coalescing of the particles to form clusters. An approach based on various effective medium theories is followed, and the modeling results are compared with those from the cases with local response and particles randomly distributed through the host medium. Possible observations of our modeling results are illustrated via a calculation of the transmission of light through a thin film made of these materials. It is found that the nonlocal effects are particularly significant when the particles coalesce, leading to blue-shifted resonances and slightly lower values in the dielectric functions. The dependence of these effects on the volume fraction and fractal dimension of the metal clusters is studied in detail.

A recipe for free-energy functionals of polarizable molecular fluids

NASA Astrophysics Data System (ADS)

Sundararaman, Ravishankar; Letchworth-Weaver, Kendra; Arias, T. A.

2014-04-01

Classical density-functional theory is the most direct approach to equilibrium structures and free energies of inhomogeneous liquids, but requires the construction of an approximate free-energy functional for each liquid of interest. We present a general recipe for constructing functionals for small-molecular liquids based only on bulk experimental properties and ab initio calculations of a single solvent molecule. This recipe combines the exact free energy of the non-interacting system with fundamental measure theory for the repulsive contribution and a weighted density functional for the short-ranged attractive interactions. We add to these ingredients a weighted polarization functional for the long-range correlations in both the rotational and molecular-polarizability contributions to the dielectric response. We also perform molecular dynamics calculations for the free energy of cavity formation and the high-field dielectric response, and show that our free-energy functional adequately describes these properties (which are key for accurate solvation calculations) for all three solvents in our study: water, chloroform, and carbon tetrachloride.

Structural, photoconductivity, and dielectric studies of polythiophene-tin oxide nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Murugavel, S., E-mail: starin85@gmail.com; Malathi, M., E-mail: mmalathi@vit.ac.in

2016-09-15

Highlights: • Synthesis of polythiophene-tin oxide nanocomposites confirmed by FTIR and EDAX. • SEM shows SnO{sub 2} nanoparticles embedded within polythiophene matrix. • Stability and isoelectric point suggest nanoparticle–matrix interaction. • High dielectric constant due to high Maxwell–Wagner interfacial polarization. - Abstract: Polythiophene-tinoxide (PT-SnO{sub 2}) nanocomposites were prepared by in situ chemical oxidative polymerization, in the presence of various concentrations of SnO{sub 2} nanoparticles. Samples were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and Zeta potential measurements. Morphologies and elemental compositions were investigated by transmission electron microscopy, field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy.more » The photoconductivity of the nanocomposites was studied by field-dependent dark and photo conductivity measurements. Their dielectric properties were investigated using dielectric spectroscopy, in the frequency range of 1kHz–1 MHz. The results indicated that the SnO{sub 2} nanoparticles in the PT-SnO{sub 2} nanocomposite were responsible for its enhanced dielectric performance.« less

Measuring and modeling of radiofrequency dielectric properties of chicken breast meat

USDA-ARS?s Scientific Manuscript database

Dielectric properties of chicken breast meat are important for both dielectric heating and quality sensing applications. In heating applications they allow optimization of energy transfer and uniformity of heating. In sensing applications, they can be used to predict quality attributes of the chicke...

Development of electroactive polymer nanocomposites with porous structured materials

NASA Astrophysics Data System (ADS)

Lopes, Ana Catarina Teixeira Castro

Electroactive polymer composites are interesting materials for advance technological applications due to the possibility to combine the electroactive properties of the polymer matrix with a large variety of fillers that allow tailored responses for specific applications. The best all-around electroactive polymers are poly(vinylidene fluoride) (PVDF) and its copolymers which allied with the properties of porous zeolite materials, with tailored shape, size and Si/Al ratio, among others, leads to the possibility of development of promising PVDF/zeolite composites. In this way, a study of the structural, thermal and electrical properties of PVDF composites prepared with different framework zeolite types (LTL, LTA, FAU and MFI), different polymer solvents (DMF, DMSO, TEP) and different zeolite (NaY) concentrations (4, 16, 24 and 32 wt %) was performed. Further, the dielectric response, electrical conductivity and electric modulus of the composites were investigated as a function of NaYzeolite content. The zeolite influence on the electroactive gamma-phase crystallization of PVDF was explored, as well as the effect of clay layered structure (Montmorillonite, Kaolinite and Laponite) on the electroactive gamma-phase nucleation and on the optical transparency of the composite. It was found that the obtained composites showed an electrical response dependence on the pore structure and chemical content of the inorganic host. The dielectric response of the composites is directly related to the Si/Al ratio, leading zeolites with lower Si/Al ratios to larger dielectric responses and encapsulation efficiencies in the composites. It was also found that the zeolite content strongly influences the macroscopic response of dielectric response, which increases for increasing filler content. The dielectric constant at room temperature reaches values larger than 1000 for the 32 wt.% composite at 1 kHz what is mainly attributed to restricted ion mobility and interfacial polarization effects due to the zeolite inclusion, leading also to high dielectric losses. For the higher zeolite concentrations the composite d.c. electrical conductivity is characterized by two conducting regimes separated by a concentration independent breaking voltage of 4 V, which is associated to an intrazeolite charge transport. Dielectric relaxation studies show that the main relaxation process (?-relaxation) of the amorphous phase of the polymer matrix is not affected by the presence of the zeolite and, in a similar way, the zeolite low temperature relaxation is not significantly affected by the polymer phase. On the other hand, the electric modulus formalism reveals significant contributions of the fillers to the electrical permittivity and conductivity of the composites. The presence of the zeolite particles increases a.c. conductivity and the Maxwell-Wagner-Sillars contribution that is predominant at low frequencies with respect to the ohmic contribution to permittivity. The ability of zeolites to induce the eletroactive gamma-phase nucleation of PVDF is directly dependent on the Si/Al ratio and zeolite content; however it only occurs when the composite is melted at temperatures below 200 ºC. The complete ?-phase crystallization of the polymer crystalline phase occurs for a filler content of 16 wt% of LTA or FAU zeolite structure. The even higher surface interaction of clays when exfoliated leads to the same phenomenon with an amount of 0.50 % of Montmorillonite clay content. The electroactivity of the material has been proven by measuring the piezoelectric d33 response of the material, which presents a value of -7 pC/N, lower than for beta-PVDF obtained by mechanical stretching but still among the largest coefficients obtained for polymers. Further, the optical transmittance in the visible range is strongly enhanced with respect to the transmittance of the pure polymer. The development, characterization and physical-chemical understanding of these PVDF/zeolite and PVDF/clay composites resulted in suitable materials for applications in diverse areas including battery separator membranes and biomedical applications.

Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mangeri, John; Espinal, Yomery; Jokisaari, Andrea M.

Here, composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO 3 or BaTiO 3 nanoparticles embedded in a dielectric medium, including air. The equilibrium polarization topology is strongly affected by particlemore » diameter, as well as the choice of inclusion and matrix materials, with monodomain, vortex-like and multidomain patterns emerging for various combinations of size and materials parameters. This leads to radically different polarization vs electric field responses, resulting in highly tunable size-dependent dielectric properties that should be possible to observe experimentally. Our calculations show that there is a critical particle size below which ferroelectricity vanishes. For the PbTiO 3 particle, this size is 2 and 3.4 nm, respectively, for high- and low-permittivity media. For the BaTiO 3 particle, it is ~3.6 nm regardless of the medium dielectric strength.« less

Topological phase transformations and intrinsic size effects in ferroelectric nanoparticles

DOE PAGES

Mangeri, John; Espinal, Yomery; Jokisaari, Andrea M.; ...

2017-01-06

Here, composite materials comprised of ferroelectric nanoparticles in a dielectric matrix are being actively investigated for a variety of functional properties attractive for a wide range of novel electronic and energy harvesting devices. However, the dependence of these functionalities on shapes, sizes, orientation and mutual arrangement of ferroelectric particles is currently not fully understood. In this study, we utilize a time-dependent Ginzburg-Landau approach combined with coupled-physics finite-element-method based simulations to elucidate the behavior of polarization in isolated spherical PbTiO 3 or BaTiO 3 nanoparticles embedded in a dielectric medium, including air. The equilibrium polarization topology is strongly affected by particlemore » diameter, as well as the choice of inclusion and matrix materials, with monodomain, vortex-like and multidomain patterns emerging for various combinations of size and materials parameters. This leads to radically different polarization vs electric field responses, resulting in highly tunable size-dependent dielectric properties that should be possible to observe experimentally. Our calculations show that there is a critical particle size below which ferroelectricity vanishes. For the PbTiO 3 particle, this size is 2 and 3.4 nm, respectively, for high- and low-permittivity media. For the BaTiO 3 particle, it is ~3.6 nm regardless of the medium dielectric strength.« less

Optically controlled dielectric properties of single-walled carbon nanotubes for terahertz wave applications.

PubMed

Smirnov, Serguei; Anoshkin, Ilya V; Demchenko, Petr; Gomon, Daniel; Lioubtchenko, Dmitri V; Khodzitsky, Mikhail; Oberhammer, Joachim

2018-06-21

Materials with tunable dielectric properties are valuable for a wide range of electronic devices, but are often lossy at terahertz frequencies. Here we experimentally report the tuning of the dielectric properties of single-walled carbon nanotubes under light illumination. The effect is demonstrated by measurements of impedance variations at low frequency as well as complex dielectric constant variations in the wide frequency range of 0.1-1 THz by time domain spectroscopy. We show that the dielectric constant is significantly modified for varying light intensities. The effect is also practically applied to phase shifters based on dielectric rod waveguides, loaded with carbon nanotube layers. The carbon nanotubes are used as tunable impedance surface controlled by light illumination, in the frequency range of 75-500 GHz. These results suggest that the effect of dielectric constant tuning with light, accompanied by low transmission losses of the carbon nanotube layer in such an ultra-wide band, may open up new directions for the design and fabrication of novel Terahertz and optoelectronic devices.

The electrical and dielectric properties of the Au/Ti/HfO2/n-GaAs structures

NASA Astrophysics Data System (ADS)

Karabulut, Abdulkerim; Türüt, Abdulmecit; Karataş, Şükrü

2018-04-01

In this work, temperature dependent electrical and dielectric properties of the Au/Ti/HfO2/n-GaAs structures were investigated using capacitance-voltage (C-V) and conductance-voltage (G-V) measurements in the temperature range of 60-320 K by steps of 20 K at 1 MHz. The dielectric constant (ε‧), dielectric loss (ε″), dielectric loss tangent (tanδ) and ac electrical conductivities (σac) have been calculated as a function of temperature. These values of the ε‧, ε″, tanδ and σac have been found to be 2.272, 5.981, 2.631 and 3.32 × 10-6 (Ω-1cm-1) at 80 K, respectively, 1.779, 2.315, 1.301 and 1.28 × 10-6 (Ω-1cm-1), respectively at 320 K. These decrease of the dielectric parameters (ε‧, ε″, tanδ and σac) have been observed at high temperatures. The experimental results show that electrical and dielectric properties are strongly temperature and bias voltage dependent.

γ-rays irradiation effects on dielectric properties of Ti/Au/GaAsN Schottky diodes with 1.2%N

NASA Astrophysics Data System (ADS)

Teffahi, A.; Hamri, D.; Djeghlouf, A.; Abboun Abid, M.; Saidane, A.; Al Saqri, N.; Felix, J. F.; Henini, M.

2018-06-01

Dielectric properties of As grown and irradiated Ti /Au/GaAsN Schottky diodes with 1.2%N are investigated using capacitance/conductance-voltage measurements in 90-290 K temperature range and 50-2000 kHz frequency range. Extracted parameters are interface state density, series resistance, dielectric constant, dielectric loss, tangent loss and ac conductivity. It is shown that exposure to γ-rays irradiation leads to reduction in effective trap density believed to result from radiation-induced traps annulations. An increase in series resistance is attributed to a net doping reduction. Dielectric constant (ε') shows usual step-like transitions with corresponding relaxation peaks in dielectric loss. These peaks shift towards lower temperature as frequency decrease. Temperature dependant ac conductivity followed an Arrhenius relation with activation energy of 153 meV in the 200-290 K temperature range witch correspond to As vacancy. The results indicate that γ-rays irradiation improves the dielectric and electrical properties of the diode due to the defect annealing effect.

Nanostructure and strain effects in active thin films for novel electronic device applications

NASA Astrophysics Data System (ADS)

Yuan, Zheng

2007-12-01

There are many potential applications of ferroelectric thin films that take advantage of their unique dielectric and piezoelectric properties, such as tunable microwave devices and thin-film active sensors for structural health monitoring (SHM). However, many technical issues still restrict practical applications of ferroelectric thin films, including high insertion loss, limited figure of merit, soft mode effect, large temperature coefficients, and others. The main theme of this thesis is the advanced technique developments, and the new ferroelectric thin films syntheses and investigations for novel device applications. A novel method of additional doping has been adopted to (Ba,Sr)TiO 3 (BSTO) thin films on MgO. By introducing 2% Mn into the stoichiometric BSTO, Mn:BSTO thin films have shown a greatly enhanced dielectric tunability and a reduced insertion loss at high frequencies (10-30 GHz). A new record of a large tunability of 80% with a high dielectric constant of 3800 and an extra low dielectric loss of 0.001 at 1 MHz at room-temperature was achieved. Meanwhile, the new highly epitaxial ferroelectric (Pb,Sr)TiO3 (PSTO) thin films have been synthesized on (001) MgO substrates. PSTO films demonstrated excellent high frequency dielectric properties with high dielectric constants above 1420 and large dielectric tunabilities above 34% at room-temperature up to 20 GHz. In addition, a smaller temperature coefficient from 80 K to 300 K was observed in PSTO films compared to BSTO films. These results indicate that the Mn:BSTO and PSTO films are both good candidates for developing room-temperature tunable microwave devices. Furthermore, crystalline ferroelectric BaTiO3 (BTO) thin films have been deposited directly on metal substrate Ni through a unique in-situ substrate pre-oxidation treatment. The highly oriented nanopillar structural BTO films were grown on the buffered layers created by the pre-oxidation treatment. No interdiffusion or reaction was observed at the interface. As-grown BTO films demonstrated good ferroelectric properties and an extremely large piezoelectric response of 130 (x 10-12 C/N). These excellent preliminary results enable the long-term perspective on the unobtrusive ferroelectric thin-film active sensors for SHM applications.

Dielectric properties of dried vegetable powders and their temperature profile during radio frequency heating

USDA-ARS?s Scientific Manuscript database

Recently, Salmonella contamination was identified in low-moisture foods including dried vegetable powder. Radio Frequency (RF) dielectric heating is a potential alternative pasteurization method with short heating time. Dielectric properties of broccoli powder with 6.9, 9.1, 12.2, and 14.9%, w. b....

Temperature dependent dielectric properties of Au/ZnO/n-Si heterojuntion

NASA Astrophysics Data System (ADS)

Kocyigit, Adem; Orak, İkram; Turut, Abdulmecit

2018-03-01

Owing to importance of ZnO in electronics, Au/ZnO/n-type Si device was fabricated to investigate its dielectric properties by aid of capacitance-conductance-voltage measurements. While the ZnO thin film layer on the n-type Si was formed by atomic layer deposition (ALD) technique, the rectifying and ohmic contacts were obtained by thermal evaporation. The surface morphology of ZnO thin film was characterized using atomic force microscopy (AFM) to show its compatibility as interfacial layer in the Au/ZnO/n-type Si device. The dielectric properties of the device were examined in terms of dielectric parameters such as dielectric constant (ɛ‧), dielectric loss (ɛ″), loss tangent (tan δ), the real and imaginary parts of electric modulus (M ‧ and M ″) and ac electrical conductivity (σ) depending on applied voltages (from -1 to 2 V) and temperatures (from 140 K to 360 K) ranges. The results have revealed that interfacial polarization and charge carriers are the important parameters to affect the dielectric properties of the device with changing temperature. The device can be used at wide range temperatures for diode applications.

Variation in dielectric properties due to pathological changes in human liver.

PubMed

Peyman, Azadeh; Kos, Bor; Djokić, Mihajlo; Trotovšek, Blaž; Limbaeck-Stokin, Clara; Serša, Gregor; Miklavčič, Damijan

2015-12-01

Dielectric properties of freshly excised human liver tissues (in vitro) with several pathological conditions including cancer were obtained in frequency range 100 MHz-5 GHz. Differences in dielectric behavior of normal and pathological tissues at microwave frequencies are discussed based on histological information for each tissue. Data presented are useful for many medical applications, in particular nanosecond pulsed electroporation techniques. Knowledge of dielectric properties is vital for mathematical calculations of local electric field distribution inside electroporated tissues and can be used to optimize the process of electroporation for treatment planning procedures. © 2015 Wiley Periodicals, Inc.

Structural, Dielectric, and Electrical Properties of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3

NASA Astrophysics Data System (ADS)

Panda, Niranjan; Pattanayak, Samita; Choudhary, R. N. P.

2015-12-01

Polycrystalline samples of Bi1- x Pb x Fe1- x (Zr0.5Ti0.5) x O3 (BPFZTO) with x = 0.0, 0.2, 0.3, and 0.4 were prepared by high-temperature solid-state reaction. Preliminary structural analysis of calcined powders of the materials by use of x-ray powder diffraction confirmed formation of single-phase systems with the tetragonal structure. Room-temperature scanning electron micrographs of the samples revealed uniform distribution of grains of low porosity and different dimensions on the surface of the samples. The frequency-temperature dependence of dielectric and electric properties was studied by use of dielectric and complex impedance spectroscopy over a wide range of frequency (1 kHz to 1 MHz) at different temperatures (25-500°C). The dielectric constant of BiFeO3 (BFO) was enhanced by substitution with Pb(Zr0.5Ti0.5)O3 (PZT) whereas the dielectric loss of the BPFZTO compounds decreased with increasing PZT content. A significant contribution of both grains and grain boundaries to the electrical response of the materials was observed. The frequency-dependence of the ac conductivity of BPFZTO followed Jonscher's power law. Negative temperature coefficient of resistance behavior was observed for all the BPFZTO samples. Conductivity by thermally excited charge carriers and oxygen vacancies in the materials was believed to be of the Arrhenius-type.

Analytical scanning evanescent microwave microscope and control stage

DOEpatents

Xiang, Xiao-Dong; Gao, Chen; Duewer, Fred; Yang, Hai Tao; Lu, Yalin

2013-01-22

A scanning evanescent microwave microscope (SEMM) that uses near-field evanescent electromagnetic waves to probe sample properties is disclosed. The SEMM is capable of high resolution imaging and quantitative measurements of the electrical properties of the sample. The SEMM has the ability to map dielectric constant, loss tangent, conductivity, electrical impedance, and other electrical parameters of materials. Such properties are then used to provide distance control over a wide range, from to microns to nanometers, over dielectric and conductive samples for a scanned evanescent microwave probe, which enable quantitative non-contact and submicron spatial resolution topographic and electrical impedance profiling of dielectric, nonlinear dielectric and conductive materials. The invention also allows quantitative estimation of microwave impedance using signals obtained by the scanned evanescent microwave probe and quasistatic approximation modeling. The SEMM can be used to measure electrical properties of both dielectric and electrically conducting materials.

Analytical scanning evanescent microwave microscope and control stage

DOEpatents

Xiang, Xiao-Dong; Gao, Chen; Duewer, Fred; Yang, Hai Tao; Lu, Yalin

2009-06-23

A scanning evanescent microwave microscope (SEMM) that uses near-field evanescent electromagnetic waves to probe sample properties is disclosed. The SEMM is capable of high resolution imaging and quantitative measurements of the electrical properties of the sample. The SEMM has the ability to map dielectric constant, loss tangent, conductivity, electrical impedance, and other electrical parameters of materials. Such properties are then used to provide distance control over a wide range, from to microns to nanometers, over dielectric and conductive samples for a scanned evanescent microwave probe, which enable quantitative non-contact and submicron spatial resolution topographic and electrical impedance profiling of dielectric, nonlinear dielectric and conductive materials. The invention also allows quantitative estimation of microwave impedance using signals obtained by the scanned evanescent microwave probe and quasistatic approximation modeling. The SEMM can be used to measure electrical properties of both dielectric and electrically conducting materials.

[Effects of simulated hypoxia on dielectric properties of mouse erythrocytes].

PubMed

Ma, Qing; Tang, Zhi-Yuan; Wang, Qin-Wen; Zhao, Xin

2008-02-01

To explore the influence of simulated altitude hypoxia on dielectric properties of mouse erythrocytes. Experimental animals were divided into the plain control group(control) and simulated altitude hypoxia group (altitude). The AC impedance of mouse erythrocytes was measured with the Agilent 4294A impedance analyzer, the influence of simulated altitude hypoxia on dielectric properties of mouse erythrocytes was observed by cell dielectric spectroscopy, Cole-Cole plots, loss factor spectrum, loss tangent spectrum, and curve fitting analysis of Cole-Cole equation. After mice were exposed to hypoxia at simulated 5000 m altitude for 4 weeks, permittivity at low frequency (epsilonl) and dielectric increment (deltaepsilon) increased 57% and 59% than that of control group respectively, conductivity at low frequency (kappal) and conductivity at high frequency (kappah) reduced 49% and 11% than that of control group respectively. The simulated altitude hypoxia could arise to increase dielectric capability and depress conductive performance on mouse erythrocytes.

Real-time detection of dielectric anisotropy or isotropy in unconventional oil-gas reservoir rocks supported by the oblique-incidence reflectivity difference technique

NASA Astrophysics Data System (ADS)

Zhan, Honglei; Wang, Jin; Zhao, Kun; Lű, Huibin; Jin, Kuijuan; He, Liping; Yang, Guozhen; Xiao, Lizhi

2016-12-01

Current geological extraction theory and techniques are very limited to adequately characterize the unconventional oil-gas reservoirs because of the considerable complexity of the geological structures. Optical measurement has the advantages of non-interference with the earth magnetic fields, and is often useful in detecting various physical properties. One key parameter that can be detected using optical methods is the dielectric permittivity, which reflects the mineral and organic properties. Here we reported an oblique-incidence reflectivity difference (OIRD) technique that is sensitive to the dielectric and surface properties and can be applied to characterization of reservoir rocks, such as shale and sandstone core samples extracted from subsurface. The layered distribution of the dielectric properties in shales and the uniform distribution in sandstones are clearly identified using the OIRD signals. In shales, the micro-cracks and particle orientation result in directional changes of the dielectric and surface properties, and thus, the isotropy and anisotropy of the rock can be characterized by OIRD. As the dielectric and surface properties are closely related to the hydrocarbon-bearing features in oil-gas reservoirs, we believe that the precise measurement carried with OIRD can help in improving the recovery efficiency in well-drilling process.

Real-time detection of dielectric anisotropy or isotropy in unconventional oil-gas reservoir rocks supported by the oblique-incidence reflectivity difference technique

PubMed Central

Zhan, Honglei; Wang, Jin; Zhao, Kun; Lű, Huibin; Jin, Kuijuan; He, Liping; Yang, Guozhen; Xiao, Lizhi

2016-01-01

Current geological extraction theory and techniques are very limited to adequately characterize the unconventional oil-gas reservoirs because of the considerable complexity of the geological structures. Optical measurement has the advantages of non-interference with the earth magnetic fields, and is often useful in detecting various physical properties. One key parameter that can be detected using optical methods is the dielectric permittivity, which reflects the mineral and organic properties. Here we reported an oblique-incidence reflectivity difference (OIRD) technique that is sensitive to the dielectric and surface properties and can be applied to characterization of reservoir rocks, such as shale and sandstone core samples extracted from subsurface. The layered distribution of the dielectric properties in shales and the uniform distribution in sandstones are clearly identified using the OIRD signals. In shales, the micro-cracks and particle orientation result in directional changes of the dielectric and surface properties, and thus, the isotropy and anisotropy of the rock can be characterized by OIRD. As the dielectric and surface properties are closely related to the hydrocarbon-bearing features in oil-gas reservoirs, we believe that the precise measurement carried with OIRD can help in improving the recovery efficiency in well-drilling process. PMID:27976746

Microwave performance of photoresist-alumina microcomposites for batch fabrication of thick polymer-based dielectric structures

NASA Astrophysics Data System (ADS)

Rashidian, Atabak; Klymyshyn, David M.; Tayfeh Aligodarz, Mohammadreza; Boerner, Martin; Mohr, Jürgen

2012-10-01

The goal of this paper is to investigate the electrical properties of photoresist-alumina microcomposites with different portions of ceramic content. Substrates of photoresist-alumina microcomposites are fabricated and a comprehensive analysis is performed to characterize their dielectric constant and dielectric loss tangent at microwave frequencies up to 40 GHz. To evaluate the performance of these materials for microwave applications, the properties of various lithographically fabricated antenna elements are examined and analysed based on the measured electrical properties. The experimental results show that the electrical properties of the photoresist composite are nonlinearly affected by ceramic content and also a minimum percentage of ceramic portion is required to improve the electrical properties of the photoresist composite. For instance, comparison of 0 wt% with 23 wt% SU8-alumina shows that no reduction is achieved for the dielectric loss tangent. Comparison of 38 wt% with 48 wt% SU8-alumina microcomposite shows that the dielectric loss tangent is improved from 0.03 to 0.01 and the dielectric constant is increased from 3.8 to 5.0 at 25 GHz. These improvements can result in superior performance for the photoresist-based microwave components.

Properties-Adjustable Alumina-Zirconia Nanolaminate Dielectric Fabricated by Spin-Coating.

PubMed

Peng, Junbiao; Wei, Jinglin; Zhu, Zhennan; Ning, Honglong; Cai, Wei; Lu, Kuankuan; Yao, Rihui; Tao, Hong; Zheng, Yanqiong; Lu, Xubing

2017-11-29

In this paper, an alumina-zirconia (Al₂O₃-ZrO₂) nanolaminate dielectric was fabricated by spin-coating and the performance was investigated. It was found that the properties of the dielectric can be adjusted by changing the content of Al₂O₃/ZrO₂ in nanolaminates: when the content of Al₂O₃ was higher than 50%, the properties of nanolaminates, such as the optical energy gap, dielectric strength (V ds ), capacitance density, and relative permittivity were relatively stable, while the change of these properties became larger when the content of Al₂O₃ was less than 50%. With the content of ZrO₂ varying from 50% to 100%, the variation of these properties was up to 0.482 eV, 2.12 MV/cm, 135.35 nF/cm², and 11.64, respectively. Furthermore, it was demonstrated that the dielectric strength of nanolaminates were influenced significantly by the number (n) of bilayers. Every increment of one Al₂O₃-ZrO 2 bilayer will enhance the dielectric strength by around 0.39 MV/cm (V ds ≈ 0.86 + 0.39n). This could be contributed to the amorphous alumina which interrupted the grain boundaries of zirconia.

Dielectric Properties of BST/(Y 2O 3) x(ZrO 2) 1-x/BST Trilayer Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahoo, Santosh K.; Misra, D.

2011-01-31

Thin films of Ba1-xSrxTiO3 (BST) are being actively investigated for applications in dynamic random access memories (DRAM) because of their properties such as high dielectric constant, low leakage current, and high dielectric breakdown strength. Various approaches have been used to improve the dielectric properties of BST thin films such as doping, graded compositions, and multilayer structures. We have found that inserting a ZrO2 layer in between two BST layers results in a significant reduction in dielectric constant as well as dielectric loss. In this work the effect of Y2O3 doped ZrO2 on the dielectric properties of BST/ZrO2/BST trilayer structure ismore » studied. The structure Ba0.8Sr0.2TiO3/(Y2O3)x(ZrO2)1-x/Ba0.8Sr0.2TiO3 is deposited by a sol-gel process on platinized Si substrate. The composition (x) of the middle layer is varied while keeping the total thickness of the trilayer film constant. The dielectric constant of the multilayer film decreases with the increase of Y2O3 amount in the film whereas there is a slight variation in dielectric loss. In Y2O3 doped multilayer thin films, the dielectric loss is lower in comparison to other films and also there is good frequency stability in the loss in the measured frequency range and hence very suitable for microwave device applications.« less

Dual-cycle dielectrophoretic collection rates for probing the dielectric properties of nanoparticles

PubMed Central

Bakewell, David J; Holmes, David

2013-01-01

A new DEP spectroscopy method and supporting theoretical model is developed to systematically quantify the dielectric properties of nanoparticles using continuously pulsed DEP collection rates. Initial DEP collection rates, that are dependent on the nanoparticle dielectric properties, are an attractive alternative to the crossover frequency method for determining dielectric properties. The new method introduces dual-cycle amplitude modulated and frequency-switched DEP (dual-cycle DEP) where the first collection rate with a fixed frequency acts as a control, and the second collection rate frequency is switched to a chosen value, such that, it can effectively probe the dielectric properties of the nanoparticles. The application of the control means that measurement variation between DEP collection experiments is reduced so that the frequency-switched probe collection is more effective. A mathematical model of the dual-cycle method is developed that simulates the temporal dynamics of the dual-cycle DEP nanoparticle collection system. A new statistical method is also developed that enables systematic bivariate fitting of the multifrequency DEP collection rates to the Clausius–Mossotti function, and is instrumental for determining dielectric properties. A Monte-Carlo simulation validates that collection rates improve estimation of the dielectric properties, compared with the crossover method, by exploiting a larger number of independent samples. Experiments using 200 nm diameter latex nanospheres suspended in 0.2 mS/m KCl buffer yield a nanoparticle conductivity of 26 mS/m that lies within 8% of the expected value. The results show that the dual-frequency method has considerable promise particularly for automated DEP investigations and associated technologies. PMID:23172363

Dielectric properties of Asteroid Vesta's surface as constrained by Dawn VIR observations

NASA Astrophysics Data System (ADS)

Palmer, Elizabeth M.; Heggy, Essam; Capria, Maria T.; Tosi, Federico

2015-12-01

Earth and orbital-based radar observations of asteroids provide a unique opportunity to characterize surface roughness and the dielectric properties of their surfaces, as well as potentially explore some of their shallow subsurface physical properties. If the dielectric and topographic properties of asteroid's surfaces are defined, one can constrain their surface textural characteristics as well as potential subsurface volatile enrichment using the observed radar backscatter. To achieve this objective, we establish the first dielectric model of asteroid Vesta for the case of a dry, volatile-poor regolith-employing an analogy to the dielectric properties of lunar soil, and adjusted for the surface densities and temperatures deduced from Dawn's Visible and InfraRed mapping spectrometer (VIR). Our model suggests that the real part of the dielectric constant at the surface of Vesta is relatively constant, ranging from 2.3 to 2.5 from the night- to day-side of Vesta, while the loss tangent shows slight variation as a function of diurnal temperature, ranging from 6 × 10-3 to 8 × 10-3. We estimate the surface porosity to be ∼55% in the upper meter of the regolith, as derived from VIR observations. This is ∼12% higher than previous estimation of porosity derived from previous Earth-based X- and S-band radar observation. We suggest that the radar backscattering properties of asteroid Vesta will be mainly driven by the changes in surface roughness rather than potential dielectric variations in the upper regolith in the X- and S-band.

Fruit and Vegetable Quality Assessment via Dielectric Sensing

PubMed Central

El Khaled, Dalia; Novas, Nuria; Gazquez, Jose A.; Garcia, Rosa M.; Manzano-Agugliaro, Francisco

2015-01-01

The demand for improved food quality has been accompanied by a technological boost. This fact enhances the possibility of improving the quality of horticultural products, leading towards healthier consumption of fruits and vegetables. A better electrical characterization of the dielectric properties of fruits and vegetables is required for this purpose. Moreover, a focused study of dielectric spectroscopy and advanced dielectric sensing is a highly interesting topic. This review explains the dielectric property basics and classifies the dielectric spectroscopy measurement techniques. It comprehensively and chronologically covers the dielectric experiments explored for fruits and vegetables, along with their appropriate sensing instrumentation, analytical modelling methods and conclusions. An in-depth definition of dielectric spectroscopy and its usefulness in the electric characterization of food materials is presented, along with the various sensor techniques used for dielectric measurements. The collective data are tabulated in a summary of the dielectric findings in horticultural field investigations, which will facilitate more advanced and focused explorations in the future. PMID:26131680

Solid-dielectric compound parabolic concentrators: on their use with photovoltaic devices.

PubMed

Goodman, N B; Ignatius, R; Wharton, L; Winston, R

1976-10-01

Prototype solid dielectric compound parabolic concentrators have been made and tested. By means of the geometry and refractive properties of a transparent solid they provide a technique for increasing the power output of silicon solar cells exposed to the sun by an amount nearly equal to the increase in effective collecting area. The response is uniform over a large angle which eliminates the necessity of diurnal tracking of the sun. The technique can be applied to the construction of thin panels and has the potential for significantly reducing, their cost per unit area.

Nonlinear effective permittivity of field grading composite dielectrics

NASA Astrophysics Data System (ADS)

Yang, Xiao; Zhao, Xiaolei; Li, Qi; Hu, Jun; He, Jinliang

2018-02-01

Field grading composite dielectrics with good nonlinear electrical properties can function as smart materials for electrical field control in a high-voltage apparatus. Besides the well-documented nonlinear conducting behavior, the field-dependent effective permittivity of field grading composites were also reported; however, in-depth research on the mechanism and influencing factors of this nonlinear permittivity are absent. This paper theoretically discusses the origin of the nonlinear effective permittivity, and the mechanism is illustrated through the waveform analysis of the nonlinear response of ZnO microvaristor/silicone rubber composites under a pure AC field. The field-dependent effective permittivity and loss property of the ZnO composites are measured by a dielectric spectrometer in both DC and AC fields under different frequencies. Through comparison of measurement results and theoretical models, the influence of the filler concentration, frequency, and time domain characteristics of the applied field on the nonlinear permittivity of the field grading composites are well explained. This paper provides insight into the nonlinear permittivity of field grading composites, and will be helpful for further tuning the performance of field grading composites.

Iron oxide nanoparticles as dielectric and piezoelectric enhancers for silicone elastomers

NASA Astrophysics Data System (ADS)

Iacob, Mihail; Tugui, Codrin; Tiron, Vasile; Bele, Adrian; Vlad, Stelian; Vasiliu, Tudor; Cazacu, Maria; Vasiliu, Ana-Lavinia; Racles, Carmen

2017-10-01

Iron oxide nanoparticles were prepared using an alkaline precipitation method to tune the reaction time so as to afford ferrihydrite with spherical morphology or goethite nanorods. These two nanoparticle types, surface-treated with a surfactant (Pluronic L81), were each incorporated in 10, 20 and 30 wt% within a polydimethylsiloxane-α,ω-diol (Mn = 60 000 g mol-1). The mixtures were processed as films and crosslinked by condensation with tetraethoxysilane at room temperature. The aged films were investigated concerning filler distribution (by SEM coupled with an energy-dispersive x-ray spectroscopy module), mechanical (tensile strength, elongation and Young’s modulus), and dielectric properties (permittivity, loss, conductivity and strength). The results show that the fillers have a relatively homogeneous distribution within the matrix and, dependent on the filler nature and amount, generally manifest a mechanical reinforcing effect and act as dielectric permittivity and strength enhancers. In addition, it has been found that the crystalline nanoparticles induce a piezoelectric response, emphasized by piezoelectric force microscopy. The improved properties of the composites make them suitable for applications in mechanical/electrical energy conversion, as theoretical estimates showed.

Highly efficient birefringent quarter-wave plate based on all-dielectric metasurface and graphene

NASA Astrophysics Data System (ADS)

Owiti, Edgar O.; Yang, Hanning; Liu, Peng; Ominde, Calvine F.; Sun, Xiudong

2018-07-01

All-dielectric metasurfaces offer remarkable properties including high efficiency and flexible control of the optical response. However, extreme, narrow bandwidth is a limitation that lowers applicability of these structures in photonic sensing applications. In this work, we numerically design and propose a switchable quarter-wave plate by hybridizing an all-dielectric metasurface with graphene. By using a single layer of graphene between a highly refractive index silicon and a silica substrate, the transmissive resonance is enhanced and broadened. Additionally, integrating graphene with silicon effectively modulates the Q-factor and the trapped magnetic modes in the silicon. A stable birefringence output is obtained and manipulated through the structure dimensions and the Fermi energy of graphene. A 95% polarization conversion ratio is achieved through converting linearly polarized light into circularly polarized light, and a 96% ellipticity ratio is obtained at the resonance wavelength. The structure is compact and has an ultrathin design thickness of 0 . 1 λ, in the telecommunication region. The above properties are essential for integration into photonic sensing devices and the structure has potential for compatibility with the CMOS devices.

Low dielectric response in enzyme active site

PubMed Central

Mertz, Edward L.; Krishtalik, Lev I.

2000-01-01

The kinetics of charge transfer depend crucially on the dielectric reorganization of the medium. In enzymatic reactions that involve charge transfer, atomic dielectric response of the active site and of its surroundings determines the efficiency of the protein as a catalyst. We report direct spectroscopic measurements of the reorganization energy associated with the dielectric response in the active site of α-chymotrypsin. A chromophoric inhibitor of the enzyme is used as a spectroscopic probe. We find that water strongly affects the dielectric reorganization in the active site of the enzyme in solution. The reorganization energy of the protein matrix in the vicinity of the active site is similar to that of low-polarity solvents. Surprisingly, water exhibits an anomalously high dielectric response that cannot be described in terms of the dielectric continuum theory. As a result, sequestering the active site from the aqueous environment inside low-dielectric enzyme body dramatically reduces the dielectric reorganization. This reduction is particularly important for controlling the rate of enzymatic reactions. PMID:10681440

Influence of sodium dodecyl sulfate concentration on the photocatalytic activity and dielectric properties of intercalated sodium dodecyl sulfate into Zn–Cd–Al layered double hydroxide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Abdullah Ahmed Ali, E-mail: abdullah2803@gmail.com; Talib, Zainal Abidin; Hussein, Mohd Zobir

2015-02-15

Highlights: • Zn–Cd–Al–LDH–DS were synthesized with different SDS concentrations. • Photocatalytic activity of samples was improved by increasing SDS concentration. • Dielectric response of LDH can be described by anomalous low frequency dispersion. • The dc conductivity values were calculated for Zn–Cd–Al–LDH–DS samples. • ESR spectra exhibited the successful intercalation of DS molecule into LDH gallery. - Abstract: Sodium dodecyl sulfate (SDS) has been successfully intercalated into Zn–Cd–Al–LDH precursor with different SDS concentrations (0.2, 0.3, 0.4, 0.5 and 1 mol L{sup −1}) using the coprecipitation method at (Zn{sup 2+} + Cd{sup 2+})/Al{sup 3+} molar ratio of 13 and pH 8.more » The structural, morphological, texture and composition properties of the synthesized (Zn–Cd–Al–LDH–DS) nanostructure were investigated using powder X-ray diffraction (PXRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR), respectively. The photocatalytic activity of these materials was developed by increasing the concentration of intercalated SDS. The absorbance spectra have been used to detect an anion in the LDH interlayer before and after the intercalation process, which confirmed the presence of the dodecyl sulfate (DS{sup −}) anion into LDH gallery after intercalation. The anomalous low frequency dispersion (ALFD) has been used to describe the dielectric response of Zn–Cd–Al–LDH–DS nanostructure using the second type of universal power law. At low frequency, the polarization effect of electrodes caused the rising in dielectric constant and loss values. An important result of the dielectric measurements is the calculated dc conductivity values, which are new in dielectric spectroscopy of LDH materials. An important result of the electron spin resonance (ESR) spectra exhibited the successful intercalation of DS molecule into LDH gallery. The g-factor value was affected by the SDS concentration which indicated changes to the environment around the DS molecule in LDH interlayer.« less

Plasmon transmutation: inducing new modes in nanoclusters by adding dielectric nanoparticles.

PubMed

Wen, Fangfang; Ye, Jian; Liu, Na; Van Dorpe, Pol; Nordlander, Peter; Halas, Naomi J

2012-09-12

Planar clusters of coupled plasmonic nanoparticles support nanoscale electromagnetic "hot spots" and coherent effects, such as Fano resonances, with unique near and far field signatures, currently of prime interest for sensing applications. Here we show that plasmonic cluster properties can be substantially modified by the addition of individual, discrete dielectric nanoparticles at specific locations on the cluster, introducing new plasmon modes, or transmuting existing plasmon modes to new ones, in the resulting metallodielectric nanocomplex. Depositing a single carbon nanoparticle in the junction between a pair of adjacent nanodisks induces a metal-dielectric-metal quadrupolar plasmon mode. In a ten-membered cluster, placement of several carbon nanoparticles in junctions between multiple adjacent nanoparticles introduces a collective magnetic plasmon mode into the Fano dip, giving rise to an additional subradiant mode in the metallodielectric nanocluster response. These examples illustrate that adding dielectric nanoparticles to metallic nanoclusters expands the number and types of plasmon modes supported by these new mixed-media nanoscale assemblies.

Ultrastable Natural Ester-Based Nanofluids for High Voltage Insulation Applications.

PubMed

Peppas, Georgios D; Bakandritsos, Aristides; Charalampakos, Vasilis P; Pyrgioti, Eleftheria C; Tucek, Jiri; Zboril, Radek; Gonos, Ioannis F

2016-09-28

Nanofluids for high voltage insulation systems have emerged as a potential substitute for liquid dielectrics in industrial applications. Nevertheless, the sedimentation of nanoparticles has been so far a serious barrier for their wide and effective exploitation. The present work reports on the development and in-depth characterization of colloidally ultrastable natural ester oil insulation systems containing iron oxide nanocrystals which lift the problem of sedimentation and phase separation. Compared to state-of-the-art systems, the final product is endowed with increased dielectric strength, faster thermal response, lower dielectric losses (decreased dissipation factor: tan δ), and very high endurance during discharge stressing. The developed nanofluid was studied and compared with a similar system containing commercial iron oxide nanoparticles, the latter demonstrating extensive sedimentation. Herein, the dielectric properties of the nanofluids are analyzed at various concentrations by means of breakdown voltage and dissipation factor measurements. The characterization techniques unequivocally demonstrate the high performance reliability of the reported nanofluid, which constitutes a significant breakthrough in the field of high voltage insulation technologies.

Dielectric properties and microstructures for various MLCCs coated with additives

NASA Astrophysics Data System (ADS)

Oh, Min Wook; Yeo, Dong Hun; Shin, Hyo Soon; Jeong, Dae Yong

2013-12-01

As electronic devices become smaller and have higher capacity, dielectric thin films are being used in the development of multilayer ceramic capacitors (MLCCs). Smaller BaTiO3 dielectric particles should be used to obtain the thickness of low dielectric layers. Further, MLCC properties are achieved through the uniform addition of various additives, but the existing method of adding nano additives has limitations. As such, this study evaluated the dielectric properties of BaTiO3 pellets after using the liquid coating method to add additives such as Dy, Mg, Mn, Cr, and Si to 150 nm BaTiO3 dielectric powder. Mn, Cr, and Si ions were each fixed at 0.1, 0.1, and 0.65 mol-%. Sintering was performed in a reducing atmosphere, and the microstructure and the dielectric properties were evaluated while varying Dy from 0.5 to 1.0 mol-% and Mg from 1.0 to 2.0 mol-%. Grain growth was observed for higher amounts of Dy, but were suppressed for higher amounts of Mg. With regards to changes in particle size, both the permittivity and the temperature coefficient of capacitance (TCC) increased with increasing particle size. The permittivity was highest for Si=0.65, Mn=0.1, Cr=0.1 Dy=0.75, and Mg=2.0 mol-%. These levels also satisfied the TCC properties of X7R. In the microstructure, the core-shell was the most developed.

Microwave dielectric properties of BNT-BT0.08 thin films prepared by sol-gel technique

NASA Astrophysics Data System (ADS)

Huitema, L.; Cernea, M.; Crunteanu, A.; Trupina, L.; Nedelcu, L.; Banciu, M. G.; Ghalem, A.; Rammal, M.; Madrangeas, V.; Passerieux, D.; Dutheil, P.; Dumas-Bouchiat, F.; Marchet, P.; Champeaux, C.

2016-04-01

We report for the first time the microwave characterization of 0.92(Bi0.5Na0.5)TiO3-0.08BaTiO3 (BNT-BT0.08) ferroelectric thin films fabricated by the sol-gel method and integrated in both planar and out-of-plane tunable capacitors for agile high-frequency applications and particularly on the WiFi frequency band from 2.4 GHz to 2.49 GHz. The permittivity and loss tangent of the realized BNT-BT0.08 layers have been first measured by a resonant cavity method working at 12.5 GHz. Then, we integrated the ferroelectric material in planar inter-digitated capacitors (IDC) and in out-of-plane metal-insulator-metal (MIM) devices and investigated their specific properties (dielectric tunability and losses) on the whole 100 MHz-15 GHz frequency domain. The 3D finite-elements electromagnetic simulations of the IDC capacitances are fitting very well with their measured responses and confirm the dielectric properties determined with the cavity method. While IDCs are not exhibiting an optimal tunability, the MIM capacitor devices with optimized Ir/MgO(100) bottom electrodes demonstrate a high dielectric tunability, of 30% at 2.45 GHz under applied voltages as low as 10 V, and it is reaching 50% under 20 V voltage bias at the same frequency. These high-frequency properties of the MIM devices integrating the BNT-BT0.08 films, combining a high tunability under low applied voltages indicate a wide integration potential for tunable devices in the microwave domain and particularly at 2.45 GHz, corresponding to the widely used industrial, scientific, and medical frequency band.

Hydration and dielectrical properties of aqueous pyrrolidinium trifluoroacetate solutions

NASA Astrophysics Data System (ADS)

Lyashchenko, A. K.; Balakaeva, I. V.; Simonova, Yu. A.; Timofeeva, L. M.

2017-10-01

Results from microwave measurements of the dielectrical properties of aqueous pyrrolidinium trifluoroacetate solutions at maximum water dispersion frequencies (13-25 GHz) and temperatures of 288, 298, and 308 K are given. The static dielectrical constants, times, and activation parameters of the dielectrical relaxation of solutions are calculated. The enthalpy and time of dielectrical relaxation activation are increased by deceleration of the motion of water molecules in the hydrate shells of ions. The changes in dielectrical parameters are in this case minimal in a series of aqueous solutions of diallylammonium salts with cations of different structures and degrees of substitution. It is shown that pyrrolidinium ions are characterized by weak hydrophobic hydration.

Structural stability, enhanced magnetic, piezoelectric, and transport properties in (1-x)BiFeO3-(x)Ba0.70Sr0.30TiO3 nanoparticles

NASA Astrophysics Data System (ADS)

Sharma, Subhash; Singh, Vikash; Anshul, Avneesh; Siqueiros, J. M.; Dwivedi, R. K.

2018-05-01

Multiferroic samples with composition (1-x)BiFeO3-(x)(Ba0.70Sr0.30)TiO3 (BFO-BST) were synthesized using a sol-gel route to study the effect of BST doping on structural, transport, and magnetic properties in BiFeO3 (BFO). X-ray diffraction studies with Rietveld analysis revealed that a phase transition occurred from rhombohedral (R3c) (0.0 ≤ × ≤ 0.15) to tetragonal (P4 mm) for x = 0.20 and nanocrystalline nature confirmed by transmission electron microscopy measurements. Piezoelectric properties improved as x increased from x = 0.0 (58 pC/N) to x = 0.20 (112 pC/N) increasing distortion in the crystal structure as evinced by Williamson-Hall analysis. Ferromagnetism was observed in doped BFO, different from the antiferromagnetic ordering in bulk BFO, indicating the noteworthy size effects and Fe-O-Fe bond angle variations in the magnetic ordering of BFO. An improvement in ferroelectric properties is observed with doping of BST compared to pristine BFO. Thermally activated conduction behavior occurred at low and high temperature regions as revealed by temperature dependent dc resistivity measurement. Effective improvements in dielectric response, meaning high dielectric constant with a low dielectric loss, were found in the doped samples.

Dielectric properties-based method for rapid and nondestructive moisture sensing in almonds

USDA-ARS?s Scientific Manuscript database

A dielectric-based method is presented for moisture determination in almonds independent of bulk density. The dielectric properties of almond were measured between 5 and 15 GHz, with a 1-GHz increments, for samples with moisture contents ranging from 4.8% to 16.5%, wet basis, bulk densities ranging ...

Frequency and temperature dependence of dielectric properties of chicken meat

USDA-ARS?s Scientific Manuscript database

Dielectric properties of chicken breast meat were measured with an open-ended coaxial-line probe between 200 MHz and 20 GHz at temperatures ranging from -20 degree C to +25 degree C. At a given temperature, the frequency dependence of the dielectric constant reveals two relaxations while those of th...

Dielectric properties of almond shells in the development of radio frequency and microwave pasteurization

USDA-ARS?s Scientific Manuscript database

To develop pasteurization treatments based on radio frequency (RF) or microwave energy, dielectric properties of almond shells were determined using an open-ended coaxial-probe with an impedance analyzer over a frequency range of 10 to 1800 MHz. Both the dielectric constant and loss factor of almond...

Controlling dielectric and relaxor-ferroelectric properties for energy storage by tuning Pb0.92La0.08Zr0.52Ti0.48O3 film thickness.

PubMed

Brown, Emery; Ma, Chunrui; Acharya, Jagaran; Ma, Beihai; Wu, Judy; Li, Jun

2014-12-24

The energy storage properties of Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films grown via pulsed laser deposition were evaluated at variable film thickness of 125, 250, 500, and 1000 nm. These films show high dielectric permittivity up to ∼1200. Cyclic I-V measurements were used to evaluate the dielectric properties of these thin films, which not only provide the total electric displacement, but also separate contributions from each of the relevant components including electric conductivity (D1), dielectric capacitance (D2), and relaxor-ferroelectric domain switching polarization (P). The results show that, as the film thickness increases, the material transits from a linear dielectric to nonlinear relaxor-ferroelectric. While the energy storage per volume increases with the film thickness, the energy storage efficiency drops from ∼80% to ∼30%. The PLZT films can be optimized for different energy storage applications by tuning the film thickness to optimize between the linear and nonlinear dielectric properties and energy storage efficiency.

Controlling Dielectric and Relaxor-Ferroelectric Properties for Energy Storage by Tuning Pb 0.92La 0.08Zr 0.52Ti 0.48O 3 Film Thickness

DOE PAGES

Brown, Emery; Ma, Chunrui; Acharya, Jagaran; ...

2014-12-24

The energy storage properties of Pb 0.92La 0.08Zr 0.52Ti 0.48O 3 (PLZT) films grown via pulsed laser deposition were evaluated at variable film thickness of 125, 250, 500, and 1000 nm. These films show high dielectric permittivity up to ~1200. Cyclic I–V measurements were used to evaluate the dielectric properties of these thin films, which not only provide the total electric displacement, but also separate contributions from each of the relevant components including electric conductivity (D1), dielectric capacitance (D2), and relaxor-ferroelectric domain switching polarization (P). Our results show that, as the film thickness increases, the material transits from a linearmore » dielectric to nonlinear relaxor-ferroelectric. And while the energy storage per volume increases with the film thickness, the energy storage efficiency drops from ~80% to ~30%. The PLZT films can be optimized for different energy storage applications by tuning the film thickness to optimize between the linear and nonlinear dielectric properties and energy storage efficiency.« less

Dielectric properties and nonlinear I-V electrical behavior of (Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics

NASA Astrophysics Data System (ADS)

Sun, Li; Ni, Qing; Guo, Jianqin; Cao, Ensi; Hao, Wentao; Zhang, Yongjia; Ju, Lin

2018-06-01

(Li1+, Al3+) co-doped CaCu3Ti4O12 ceramics (CaCu3-2 x Li x Al x Ti4O12, x = 0.05, 0.1, 0.15) were prepared by a sol-gel method and were sintered at 1020-1080 °C for 8 h to improve the geometric microstructure, dielectric and nonlinear I-V electrical properties. Notably, very high dielectric constant of 1 × 105 with good dielectric-frequency as well as dielectric-temperature stability can be achieved in CaCu2.8Li0.1Al0.1Ti4O12 ceramic sintered at 1060 °C. The average grain sizes, resistivity and the non-Ohmic properties are also improved compared to pure CaCu3Ti4O12. These results indicate that (Li1+, Al3+) co-doping at the Cu2+ site can improve the dielectric properties of CaCu3Ti4O12, supporting the internal barrier layer capacitance effect of Schottky barriers at grain boundaries.

An empirical model for the complex dielectric permittivity of soils as a function of water content

NASA Technical Reports Server (NTRS)

Wang, J. R.; Chmugge, T. J.

1978-01-01

The recent measurements on the dielectric properties of soils shows that the variation of dielectric constant with moisture content depends on soil types. The observed dielectric constant increases only slowly with moisture content up to a transition point. Beyond the transition it increases rapidly with moisture content. The moisture value of transition region was found to be higher for high clay content soils than for sandy soils. Many mixing formulas were compared with, and were found incompatible with, the measured dielectric variations of soil-water mixtures. A simple empirical model was proposed to describe the dielectric behavior of ths soil-water mixtures. The relationship between transition moisture and wilting point provides a means of estimating soil dielectric properties on the basis of texture information.

Synthesis, microstructure and dielectric properties of zirconium doped barium titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Rohtash; School of Physical Sciences, Jawaharlal Nehru University, New Delhi; Asokan, K.

2016-05-23

We report on synthesis, microstructural and relaxor ferroelectric properties of Zirconium(Zr) doped Barium Titanate (BT) samples with general formula Ba(Ti{sub 1-x}Zr{sub x})O{sub 3} (x=0.20, 0.35). These lead-free ceramics were prepared by solid state reaction route. The phase transition behavior and temperature dependent dielectric properties and composition dependent ferroelectric properties were investigated. XRD analysis at room temperature confirms phase purity of the samples. SEM observations revealed retarded grain growth with increasing Zr mole fraction. Dielectric properties of BZT ceramics is influenced significantly by small addition of Zr mole fraction. With increasing Zr mole fraction, dielectric constant decreases while FWHM and frequencymore » dispersion increases. Polarization vs electric field hysteresis measurements reveal ferroelectric relaxor phase at room temperature. The advantages of such substitution maneuvering towards optimizing ferroelectric properties of BaTiO{sub 3} are discussed.« less

Effect of mechanical alloying synthesis process on the dielectric properties of (Bi{sub 0.5}Na{sub 0.5}){sub 0.94}Ba{sub 0.06}TiO{sub 3} piezoceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghazanfari, Mohammad Reza, E-mail: Ghazanfari.mr@gmail.com; Amini, Rasool; Shams, Seyyedeh Fatemeh

Highlights: • MA samples show higher dielectric permittivity and Curie temperature. • In MA samples, dielectric loss is almost 27% less than conventional ones. • In MA samples, sintering time and temperature are lower than conventional ones. • In MA samples, particle morphology is more homogeneous conventional ones. • In MA samples, crystallite size is smaller conventional ones. - Abstract: In present work, in order to study the effects of synthesis techniques on dielectric properties, the BNBT lead-free piezoceramics with (Bi{sub 0.5}Na{sub 0.5}){sub 0.94}Ba{sub 0.06}TiO{sub 3} stoichiometry (called as BNBT6) were synthesized by mechanical alloying (MA) and conventional mixed oxidesmore » methods. The structural, microstructural, and dielectric properties were carried out by X-ray diffractometer (XRD), scanning electron microscope (SEM), and impedance analyzer LCR meter, respectively. Based on results, the density of MA samples is considerably higher than conventional samples owning to smaller particles size and more uniformity of particle shape of MA samples. Moreover, the dielectric properties of MA samples are comparatively improved in which the dielectric loss of these samples is almost 27% less than conventional ones. Furthermore, MA samples exhibit obviously higher dielectric permittivity and Curie temperature compared to the conventional samples.« less

Effect of surface moisture on dielectric behavior of ultrafine BaTiO3 particulates.

NASA Technical Reports Server (NTRS)

Mountvala, A. J.

1971-01-01

The effects of adsorbed H2O on the dielectric properties of ultrafine BaTiO3 particulates of varying particle size and environmental history were determined. The dielectric behavior depends strongly on surface hydration. No particle size dependence of dielectric constant was found for dehydroxylated surfaces in ultrafine particulate (unsintered) BaTiO3 materials. For equivalent particle sizes, the ac conductivity is sensitive to surface morphology. Reactions with H2O vapor appear to account for the variations in dielectric properties. Surface dehydration was effectively accomplished by washing as-received powders in isopropanol.

The Effect of Multi Wall Carbon Nanotubes on Some Physical Properties of Epoxy Matrix

NASA Astrophysics Data System (ADS)

Al-Saadi, Tagreed M.; hammed Aleabi, Suad; Al-Obodi, Entisar E.; Abdul-Jabbar Abbas, Hadeel

2018-05-01

This research involves using epoxy resin as a matrix for making a composite material, while the multi wall carbon nanotubes (MWNCTs) is used as a reinforcing material with different fractions (0.0,0.02, 0.04, 0.06) of the matrix weight. The mechanical ( hardness ), electrical ( dielectric constant, dielectric loss factor, dielectric strength, electrical conductivity ), and thermal properties (thermal conductivity ) were studied. The results showed the increase of hardness, thermal conductivity, electrical conductivity and break down strength with the increase of MWCNT concentration, but the behavior of dielectric loss factor and dielectric constant is opposite that.

Microwave dielectric study of polar liquids at 298 K

NASA Astrophysics Data System (ADS)

Maharolkar, Aruna P.; Murugkar, A.; Khirade, P. W.

2018-05-01

Present paper deals with study of microwave dielectric properties like dielectric constant, viscosity, density and refractive index for the binary mixtures of Dimethylsulphoxide (DMSO) and Methanol over the entire concentration range were measured at 298K. The experimental data further used to determine the excess properties viz. excess static dielectric constant, excess molar volume, excess viscosity& derived properties viz. molar refraction&Bruggman factor. The values of excess properties further fitted with Redlich-Kister (R-K Fit) equation to calculate the binary coefficients and standard deviation. The resulting excess parameters are used to indicate the presence of intermolecular interactions and strength of intermolecular interactions between the molecules in the binary mixtures. Excess parameters indicate structure breaking factor in the mixture predominates in the system.

Material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties produced using multi-wall carbon nanotubes wrapped with poly(ether sulphone) in a poly(ether ether ketone) matrix

NASA Astrophysics Data System (ADS)

Zhang, Shuling; Wang, Hongsong; Wang, Guibin; Jiang, Zhenhua

2012-07-01

A material with high dielectric constant, low dielectric loss, and good mechanical and thermal properties was produced using multi-wall carbon nanotubes (MWCNTs) wrapped with poly(ether sulphone) (PES) dispersed in a poly(ether ether ketone) (PEEK) matrix. The material was fabricated using melt-blending, and MWCNT/PEEK composites show different degrees of improvement in the measured dielectric, mechanical, and thermal properties as compared to pure PEEK. This is attributed to the high conductivity of MWCNTs, the effect of wrapping MWCNTs with PES, the good dispersion of the wrapped MWCNTs in PEEK, and the strong interfacial adhesion between the wrapped MWCNTs and the PEEK.

ZrO2 Layer Thickness Dependent Electrical and Dielectric Properties of BST/ZrO2/BST Multilayer Thin Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sahoo, S. K.; Misra, D.; Agrawal, D. C.

2011-01-01

Recently, high K materials play an important role in microelectronic devices such as capacitors, memory devices, and microwave devices. Now a days ferroelectric barium strontium titanate [Ba{sub x}Sr{sub 1-x}TiO{sub 3}, (BST)] thin film is being actively investigated for applications in dynamic random access memories (DRAM), field effect transistor (FET), and tunable devices because of its properties such as high dielectric constant, low leakage current, low dielectric loss, and high dielectric breakdown strength. Several approaches have been used to optimize the dielectric and electrical properties of BST thin films such as doping, graded compositions, and multilayer structures. We have found thatmore » inserting a ZrO{sub 2} layer in between two BST layers results in a significant reduction in dielectric constant, loss tangent, and leakage current in the multilayer thin films. Also it is shown that the properties of multilayer structure are found to depend strongly on the sublayer thicknesses. In this work the effect of ZrO{sub 2} layer thickness on the dielectric, ferroelectric as well as electrical properties of BST/ZrO{sub 2}/BST multilayer structure is studied. The multilayer Ba{sub 0.8}Sr{sub 0.2}TiO{sub 3}/ZrO{sub 2}/Ba{sub 0.8}Sr{sub 0.2}TiO{sub 3} film is deposited by a sol-gel process on the platinized Si substrate. The thickness of the middle ZrO{sub 2} layer is varied while keeping the top and bottom BST layer thickness as fixed. It is observed that the dielectric constant, dielectric loss tangent, and leakage current of the multilayer films reduce with the increase of ZrO{sub 2} layer thickness and hence suitable for memory device applications. The ferroelectric properties of the multilayer film also decrease with the ZrO{sub 2} layer thickness.« less

Terahertz Artificial Dielectric Lens.

PubMed

Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M

2016-03-14

We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

Terahertz Artificial Dielectric Lens

PubMed Central

Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

2016-01-01

We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices. PMID:26973294

Magnetically tunable liquid dielectric with giant dielectric permittivity based on core-shell superparamagnetic iron oxide.

PubMed

Vinayasree, S; Nitha, T S; Tiwary, C S; Ajayan, P M; Joy, P A; Anantharaman, M R

2018-06-29

A liquid dielectric based on a core-shell architecture having a superparamagnetic iron oxide core and a shell of silicon dioxide was synthesized. The frequency dependence of dielectric properties was evaluated for different concentrations of iron oxide. The dependence of magnetic field on the dielectric properties was also studied. Aqueous ferrofluid exhibited a giant dielectric constant of 6.4 × 10 5 at 0.1 MHz at a concentration of 0.2 vol% and the loss tangent was 3. The large rise in dielectric constant at room temperature is modelled and explained using percolation theory and Maxwell-Wagner-Sillars type polarization. The ferrofluid is presumed to consist of nanocapacitor networks which are wired in series along the lateral direction and parallel along longitudinal direction. On the application of an external magnetic field, the chain formation and its alignment results in the variation of dielectric permittivity.

Dielectric relaxation and electrical conduction mechanism in A2HoSbO6 (A=Ba, Sr, Ca) Double Perovskite Ceramics: An impedance spectroscopic analysis

NASA Astrophysics Data System (ADS)

Halder, Saswata; Dutta, Alo; Sinha, T. P.

2017-03-01

The AC electrical properties of polycrystalline double perovskite oxides A2HoSbO6 (A=Ba, Sr, Ca; AHS) synthesized by solid state reaction technique has been explored by using impedance spectroscopic studies. The Rietveld refinement of the room temperature X-ray diffraction data show that Ba2HoSbO6 (BHS) has cubic phase and Sr2HoSbO6 (SHS) and Ca2HoSbO6 (CHS) crystallize in monoclinic phase. The samples show significant frequency dispersion in their dielectric properties. The polydispersive nature of the relaxation mechanism is explained by the modified Cole-Cole model. The scaling behavior of dielectric loss indicate the temperature independence of the relaxation mechanism. The magnitude of the activation energy indicates that the hopping mechanism is responsible for carrier transport in AHS. The frequency dependent conductivity spectra follow the double power law. Impedance spectroscopic data presented in the Nyquist plot (Z" versus Z‧) are used to identify an equivalent circuit along with to know the grain, grain boundary and interface contributions. The constant phase element (CPE) is used to analyze the experimental response of BHS, SHS and CHS comprehending the contribution of different microstructural features to the conduction process. The temperature dependent electrical conductivity shows a semiconducting behavior.

Effects of Interphase Modification and Biaxial Orientation on Dielectric Properties of Poly(ethylene terephthalate)/Poly(vinylidene fluoride-co-hexafluoropropylene) Multilayer Films.

PubMed

Yin, Kezhen; Zhou, Zheng; Schuele, Donald E; Wolak, Mason; Zhu, Lei; Baer, Eric

2016-06-01

Recently, poly(vinylidene fluoride) (PVDF)-based multilayer films have demonstrated enhanced dielectric properties, combining high energy density and high dielectric breakdown strength from the component polymers. In this work, further enhanced dielectric properties were achieved through interface/interphase modulation and biaxial orientation for the poly(ethylene terephthalate)/poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoropropylene) [PET/PMMA/P(VDF-HFP)] three-component multilayer films. Because PMMA is miscible with P(VDF-HFP) and compatible with PET, the interfacial adhesion between PET and P(VDF-HFP) layers should be improved. Biaxial stretching of the as-extruded multilayer films induced formation of highly oriented fibrillar crystals in both P(VDF-HFP) and PET, resulting in improved dielectric properties with respect to the unstretched films. First, the parallel orientation of PVDF crystals reduced the dielectric loss from the αc relaxation in α crystals. Second, biaxial stretching constrained the amorphous phase in P(VDF-HFP) and thus the migrational loss from impurity ions was reduced. Third, biaxial stretching induced a significant amount of rigid amorphous phase in PET, further enhancing the breakdown strength of multilayer films. Due to the synergistic effects of improved interfacial adhesion and biaxial orientation, the PET/PMMA/P(VDF-HFP) 65-layer films with 8 vol % PMMA exhibited optimal dielectric properties with an energy density of 17.4 J/cm(3) at breakdown and the lowest dielectric loss. These three-component multilayer films are promising for future high-energy-density film capacitor applications.

A molecular Debye-Hückel theory and its applications to electrolyte solutions: The size asymmetric case

DOE PAGES

Xiao, Tiejun; Song, Xueyu

2017-03-28

We developed a molecular Debye-Hückel theory for electrolyte solutions with size asymmetry, where the dielectric response of an electrolyte solution is described by a linear combination of Debye-Hückel-like response modes. Furthermore, as the size asymmetry of an electrolyte solution leads to a charge imbalanced border zone around a solute, the dielectric response to the solute is characterized by two types of charge sources, namely, a bare solute charge and a charge distribution due to size asymmetry. These two kinds of charge sources are screened by the solvent differently, our theory presents a method to calculate the mean electric potential asmore » well as the electrostatic contributions to thermodynamic properties. Finally, the theory was successfully applied to binary as well as multi-component primitive models of electrolyte solutions.« less

Nonlinear dielectric properties and tunability of 0.9Pb(Mg1/3,Nb2/3)O3-0.1 PbTiO3 and Ba(Ti0.85,Sn0.15)O3 paraelectrics

NASA Astrophysics Data System (ADS)

Akdogan, E. K.; Hall, A.; Simon, W. K.; Safari, A.

2007-01-01

We investigate the nonlinear dielectric properties of 0.9Pb(Mg1/3,Nb2/3)O3•0.1PbTiO3 (PMN-PT) and Ba[Ti0.85,Sn0.15]O3 (BTS) paraelectrics experimentally and theoretically. We measure the nonlinear dielectric response in the parallel plate capacitor configuration, whereby we obtain the low frequency linear permittivity (ε33), and the higher order permittivities (ε3333,ε333333) at 298K as ε33PMN-PT=2.1×10-7 and ε33BTS=4.1×10-8F /m, ε3333PMN-PT=-4.9×10-20 and ε3333BTS=-7.3×10-21F3m /C2, and ε333333PMN-PT=7.6×10-33 and ε333333BTS=9.85×10-34F5m3/C4. By using a self-consistent thermodynamic theory in conjunction with the experimental data, we compute the E3 dependence of electrostatic free energy ΔG, the field-induced polarization P3, and the thermodynamic tunability ∂2P3/∂E32, and prove that electrostatic free energy has to be expanded at least up to the sixth order in the electric field to define the critical field ∣E3*∣ at which maximum tunability is attained. We also show that ∣E3*∣ is a function on ∣ε3333∣/ε333333 only. Consequently, we find ∣E3*∣PMN-PT=8.0×105V /m and ∣E3*∣BTS=8.6×105V/m. We compute the engineering tunabilities as ΓPMN-PT=65% and ΓBTS=55%, and then define a normalized tunability ξ to take into account the ∣E3*∣ parameter. Thereof, we determine ∣ξ ∣PMT-PT=8.1×10-5%/Vm-1 and ∣ξ∣BTS=6.4×10-5%/Vm-1. Our results reveal that ∣E3*∣BTS>∣E3*∣PMN-PT although ΓBTS<ΓPMN-PT, unequivocally showing the need for defining a critical field parameter in evaluating the nonlinear dielectric response and tunability, in particular, and in nonlinear dielectrics in general. The results also indicate that the nonlinear dielectric properties of PMN-PT are an order of magnitude higher than that of BTS, which we discuss in the context of structure-property relations of relaxors.

Dielectric response of asphaltene in solvents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheu, E.Y.; De Tar, M.M.; Storm, D.A.

1993-12-31

Asphaltenes derived from Ratawi (Neutral Zone) crude oil, by heptane extraction, self-associate in toluene. The structure of the disperse aggregates are similar to water-in-oil microemulsion droplets. The origin of the self-association is not yet understood, but has been speculated to be related to the electric properties of asphaltenes. In this study, the authors measured the dielectric response as a function of applied frequency from 1 kHz to 10 MHz. The results suggest that the charge dynamics is confined within a spatial length scale similar to the aggregate size. This indicates that the aggregates are more conductive than the continuous (toluene)more » phase. Additionally, the authors analyzed the loss modules using the Cole-Cole equation, form which the inter-aggregate interactions were determined.« less

Three dimensional reflectance properties of superconductor-dielectric photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, G. N., E-mail: gnpandey@amity.edu; Sancheti, Bhagyashree; Pandey, J. P.

2016-05-06

In this present communication, we have studied the optical properties of Photonics Crystals with super conducting constituent using the TMM method for a stratified medium. We also studied the three dimensional reflectance property of superconductor-dielectric photonic crystal at different temperature and thickness. From above study we show that the superconductor-dielectric photonic crystal may be used as broad band reflector and omnidirectional reflector at low temperature below to the critical temperature. Such property may be applied to make of the reflector which can be used in low temperature region.

Lead free dielectric ceramic with stable relative permittivity of 0.90(Na0.50Bi0.50Ti)O3-0.10AgNbO3

NASA Astrophysics Data System (ADS)

Verma, Anita; Yadav, Arun Kumar; Kumar, Sunil; Sen, Somaditya

2018-04-01

Structural, dielectric and ferroelectric properties in perovskite 0.90(Na0.50Bi0.50Ti)03-0.10AgNb03 polycrystalline powders prepared by sol-gel method are discussed. Diffuse phase transition and new type of dielectric anomaly was observed with highly steady capacitive properties in the 135-450 °C temperature range. This compound shows remarkable dielectric with dielectric constant ɛr 1000 with a variation of ± 7% and tan δ = 0.004 0.25 in 135- 450 °C temperature. In addition, it also showed excellent ferroelectric properties with saturation polarization Ps = 13.5 μC/cm2, remnant polarization of Pr = 7.6 μC/cm2 and a low coercive field Ec = 36 kV/cm at room temperature. Stable dielectric constant (ɛr) and low dielectric loss (tan δ) in a wide temperature range observed for the titled composition makes it an interesting candidate for potential use in fast growing "high-temperature electronics" industry applications.

The Study of Electrical Properties for Multilayer La2O3/Al2O3 Dielectric Stacks and LaAlO3 Dielectric Film Deposited by ALD.

PubMed

Feng, Xing-Yao; Liu, Hong-Xia; Wang, Xing; Zhao, Lu; Fei, Chen-Xi; Liu, He-Lei

2017-12-01

The capacitance and leakage current properties of multilayer La 2 O 3 /Al 2 O 3 dielectric stacks and LaAlO 3 dielectric film are investigated in this paper. A clear promotion of capacitance properties is observed for multilayer La 2 O 3 /Al 2 O 3 stacks after post-deposition annealing (PDA) at 800 °C compared with PDA at 600 °C, which indicated the recombination of defects and dangling bonds performs better at the high-k/Si substrate interface for a higher annealing temperature. For LaAlO 3 dielectric film, compared with multilayer La 2 O 3 /Al 2 O 3 dielectric stacks, a clear promotion of trapped charges density (N ot ) and a degradation of interface trap density (D it ) can be obtained simultaneously. In addition, a significant improvement about leakage current property is observed for LaAlO 3 dielectric film compared with multilayer La 2 O 3 /Al 2 O 3 stacks at the same annealing condition. We also noticed that a better breakdown behavior for multilayer La 2 O 3 /Al 2 O 3 stack is achieved after annealing at a higher temperature for its less defects.

Research on sintering behavior and microwave dielectric property of (Mg0.95Ca0.05)TiO3 ceramics for cross coupling filter

NASA Astrophysics Data System (ADS)

Luo, Chunya; Ma, Zhichao; Hu, Laisheng; Hu, Mingzhe; Huang, Xiaomin

2015-12-01

The microwave dielectric properties of 0.95%MgTiO3-0.05%CaTiO3 (abbreviated as 95MCT hereafter) ceramics have been studied for application in dielectric cross coupling filters. ZnO and Nb2O5 were selected as liquid sintering aids to lower the sintering temperature and enhance the Qf value of 95MCT and simultaneously we varied the mole ratio of ZnO : Nb2O5 to tune the microwave dielectric properties of 95MCT. When the ZnO : Nb2O5 mole ratio was 1.5 and the co-doping content was 0.25 wt.%, the optimal sintering temperature of 95MCT ceramic could be lowered from 1400∘C to 1320∘C and the Qf value could be improved by about 7.7%. The optimal microwave dielectric properties obtained under this condition were Qf = 72730 GHz (6.8 GHz), ɛr = 20.29 and τf = -6.84ppm/∘C, which demonstrated great potential usage in ceramic industry. High values of Qf ceramic were used to design the dielectric cross coupling filter. The dielectric filter measured at 2.35 GHz exhibited a 6.7% bandwidth (insert loss > -3 dB) of center frequency.

Water and ion transport in ultra-adsorbing porous magnesium carbonate studied by dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Pochard, Isabelle; Frykstrand, Sara; Ahlström, Olle; Forsgren, Johan; Strømme, Maria

2014-01-01

Porous materials are used in application areas ranging from drug and vaccine delivery, medical implants, molecular sieves and cosmetics to catalysis and humidity control. In the present work, we employed an alternative approach to gain in-depth understanding about water interaction properties in such materials by the use of dielectric spectroscopy and thereby show that it is possible to obtain information that is not accessible from the more commonly employed water interaction analysis techniques. Specifically, the complex dielectric response of Upsalite, a novel, super-hydroscopic, high-surface area, porous magnesium carbonate material was measured in isothermal frequency scans between 10-3 and 106 Hz at controlled relative humidity (RH). We found the dielectric constant of the dry material to be 1.82. The ratio of bound to free water present in Upsalite after adsorption at room temperature was found to be high irrespective of the surrounding humidity with values ranging from ˜67% to ˜90%. We further found that OH- ions are the charge carriers responsible for the electrode polarization observed in the dielectric response and that the amount of these ions that are free to move in the material corresponds to a concentration of the order of 1-10 μmol l-1 independent of RH. Finally, the OH- diffusion coefficient displayed a drastic decrease with decreasing RH, typical of transport in unsaturated conditions. The presented results provide detailed insight about water interactions in the novel water adsorbing material under study and it is foreseen that the employed analysis methods can be used to evaluate other types of moisture adsorbing materials as well as the movement of functional species in the pores of inorganic drug delivery materials and materials tailored for adsorption of harmful charged species.

Parametric Dielectric Model of Comet Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Heggy, E.; Palmer, E. M.; Kofman, W. W.; Clifford, S. M.; Righter, K.; Herique, A.

2012-12-01

In 2014, the European Space Agency's Rosetta mission is scheduled to rendezvous with Comet 67P/Churyumov-Gerasimenko (Comet 67P). Rosetta's CONSERT experiment aims to explore the cometary nucleus' geophysical properties using radar tomography. The expected scientific return and inversion algorithms are mainly dependent on our understanding of the dielectric properties of the comet nucleus and how they vary with the spatial distribution of geophysical parameters. Using observations of comets 9P/Tempel 1 and 81P/Wild 2 in combination with dielectric laboratory measurements of temperature, porosity, and dust-to-ice mass ratio dependencies for cometary analog material, we have constructed two hypothetical three-dimensional parametric dielectric models of Comet 67P's nucleus to assess different dielectric scenarios of the inner structure. Our models suggest that dust-to-ice mass ratios and porosity variations generate the most significant measurable dielectric contrast inside the comet nucleus, making it possible to explore the structural and compositional hypotheses of cometary nuclei. Surface dielectric variations, resulting from temperature changes induced by solar illumination of the comet's faces, have also been modeled and suggest that the real part of the dielectric constant varies from 1.9 to 3.0, hence changing the surface radar reflectivity. For CONSERT, this variation could be significant at low incidence angles, when the signal propagates through a length of dust mantle comparable to the wavelength. The overall modeled dielectric permittivity spatial and temporal variations are therefore consistent with the expected deep penetration of CONSERT's transmitted wave through the nucleus. It is also clear that changes in the physical properties of the nucleus induce sufficient variation in the dielectric properties of cometary material to allow their inversion from radar tomography.

Diurnal changes in the dielectric properties and water status of eastern hemlock and red spruce from Howland, ME

NASA Technical Reports Server (NTRS)

Salas, W. A.; Ranson, K. J.; Rock, B. N.; Moss, D. M.

1991-01-01

The diurnal characteristics of microwave dielectric properties and water potential of two conifer species were investigated in July and September, 1990. P-band and C-band radial dielectric profiles of hemlock and red spruce, as well as hemlock diurnal water potential and dielectric profiles, are presented. The resulting radial dielectric profiles matched the regions of the functional sapwood (water transport component of the active xylem) in both species such that the sapwood was characterized by a higher dielectric than the bark and heartwood tissues. This is probably due to characteristic differences in the water content of each tissue. As the hemlocks progressed through their diurnal water potential pattern, the dielectric profile remained static until mid-afternoon. As the tension in the water column relaxed (2 to 3 bars) the dielectric constant decreased by 30 to 40 percent. There are several possible explanations for this phenomenon, and these may relate to the dependency of the dielectric measurements on temperature, salinity, and volumetric water content.

Broadband dielectric response of CaCu3Ti4O12 : From dc to the electronic transition regime

NASA Astrophysics Data System (ADS)

Kant, Ch.; Rudolf, T.; Mayr, F.; Krohns, S.; Lunkenheimer, P.; Ebbinghaus, S. G.; Loidl, A.

2008-01-01

We report on phonon properties and electronic transitions in CaCu3Ti4O12 , a material which reveals a colossal dielectric constant at room temperature without any ferroelectric transition. The results of far- and midinfrared measurements are compared to those obtained by broadband dielectric and millimeter-wave spectroscopy on the same single crystal. The unusual temperature dependence of phonon eigenfrequencies, dampings, and ionic plasma frequencies of low-lying phonon modes is analyzed and discussed in detail. Electronic excitations below 4eV are identified as transitions between full and empty hybridized oxygen-copper bands and between oxygen-copper and unoccupied Ti3d bands. The unusually small band gap determined from the dc conductivity (˜200meV) compares well with the optical results.

Effects of applied electric field during postannealing on the tunable properties of (Ba,Sr)TiO3 thin films

NASA Astrophysics Data System (ADS)

Xia, Yidong; Cheng, Jinbo; Pan, Bai; Wu, Di; Meng, Xiangkang; Liu, Zhiguo

2005-08-01

The impact of postannealing in electric field on the structure, tunability, and dielectric behavior of rf magnetron sputtering derived (Ba,Sr)TiO3 films has been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability remarkably and destroy the symmetry of capacitance-voltage characteristics of the films. The increased out-of-plane lattice constant and the appearance of the hysteresis loops in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature.

Numerical studies on the electromagnetic properties of the nonlinear Lorentz Computational model for the dielectric media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abe, H.; Okuda, H.

We study linear and nonlinear properties of a new computer simulation model developed to study the propagation of electromagnetic waves in a dielectric medium in the linear and nonlinear regimes. The model is constructed by combining a microscopic model used in the semi-classical approximation for the dielectric media and the particle model developed for the plasma simulations. It is shown that the model may be useful for studying linear and nonlinear wave propagation in the dielectric media.

Development and study of a heat pipe with dielectric properties

NASA Astrophysics Data System (ADS)

Semena, M. G.; Gershuni, A. N.; Chepurnoi, A. B.

Requirements for the structural elements of heat pipes with dielectric properties are examined. To obtain information necessary for the thermal analysis of heat pipes, a study is made of the capillary-transport characteristics of a dielectric capillary structure consisting of quartz fibers; the capillary pressure and the liquid penetration coefficient are determined. The results of the study are used to develop dielectric heat pipes for the cooling of a vacuum electronic instrument. Experimentally determined characteristics of the heat pipes are presented.

Dielectric Spectroscopy Study of ZnSe Grown by Physical Vapor Transport

NASA Technical Reports Server (NTRS)

Kokan, J.; Gerhardt, R.; Su, Ching-Hua

1997-01-01

The dielectric properties of ZnSe samples grown by physical vapor transport were measured as a function of frequency. Differences can be seen in the dielectric properties of samples grown under different conditions. The spectra of heat treated samples were also acquired and were found to exhibit significant deviations from those of the as grown crystals.

Assessing Chicken Meat Freshness through Measurement of Radio-Frequency Dielectric Properties

USDA-ARS?s Scientific Manuscript database

Change in freshness of chicken meat was assessed through measurement of the dielectric properties with a vector network analyzer and an open-ended coaxial-line probe between 200 MHz and 20 GHz at 23 oC. Chicken meat samples were stored in a refrigerator for 8 days at 4 oC. Changes in dielectric cons...

Investigating the influence of aging on radiofrequency dielectric properties of chicken meat

USDA-ARS?s Scientific Manuscript database

Changes in quality attributes of aging chicken meat were tracked through measurement of the dielectric properties with an open-ended coaxial probe between 200 MHz and 20 GHz at 23 degree C. The chicken meat was stored in a refrigerator for 8 days at 4 degree C. Changes in dielectric constant and los...

Measurement of complex terahertz dielectric properties of polymers using an improved free-space technique

NASA Astrophysics Data System (ADS)

Chang, Tianying; Zhang, Xiansheng; Yang, Chuanfa; Sun, Zhonglin; Cui, Hong-Liang

2017-04-01

The complex dielectric properties of non-polar solid polymer materials were measured in the terahertz (THz) band by a free-space technique employing a frequency-extended vector network analyzer (VNA), and by THz time-domain spectroscopy (TDS). Mindful of THz wave’s unique characteristics, the free-space method for measurement of material dielectric properties in the microwave band was expanded and improved for application in the THz frequency region. To ascertain the soundness and utility of the proposed method, measurements of the complex dielectric properties of a variety of polymers were carried out, including polytetrafluoroethylene (PTFE, known also by the brand name Teflon), polypropylene (PP), polyethylene (PE), and glass fiber resin (Composite Stone). The free-space method relies on the determination of electromagnetic scattering parameters (S-parameters) of the sample, with the gated-reflect-line (GRL) calibration technique commonly employed using a VNA. Subsequently, based on the S-parameters, the dielectric constant and loss characteristic of the sample were calculated by using a Newtonian iterative algorithm. To verify the calculated results, THz TDS technique, which produced Fresnel parameters such as reflection and transmission coefficients, was also used to independently determine the dielectric properties of these polymer samples, with results satisfactorily corroborating those obtained by the free-space extended microwave technique.

Microstructures and dielectric properties of CaCu3Ti4O12 ceramics via combustion method

NASA Astrophysics Data System (ADS)

Yuan, W. X.; Li, Z. J.

2012-01-01

CaCu3Ti4O12 (CCTO) powder was synthesized by the combustion method. The effect of sintering temperature was studied on dielectric properties of the prepared ceramic samples. They have the dielectric constant of ~31 000 and 80 000 for the grain size of 0.3 and 30-100 μm. It is unusual for CCTO with a grain size of 0.3 μm to have a dielectric constant of ~31 000. Their giant dielectric constant could be explained by a two-step internal-barrier-layer-capacitor model, associated with grain boundaries and domain boundaries. The existence of domain boundaries helped to explain the contradiction of the dielectric mechanisms between polycrystalline and single-crystal CCTO.

Local representation of the electronic dielectric response function

DOE PAGES

Lu, Deyu; Ge, Xiaochuan

2015-12-11

We present a local representation of the electronic dielectric response function, based on a spatial partition of the dielectric response into contributions from each occupied Wannier orbital using a generalized density functional perturbation theory. This procedure is fully ab initio, and therefore allows us to rigorously define local metrics, such as “bond polarizability,” on Wannier centers. We show that the locality of the bare response function is determined by the locality of three quantities: Wannier functions of the occupied manifold, the density matrix, and the Hamiltonian matrix. Furthermore, in systems with a gap, the bare dielectric response is exponentially localized,more » which supports the physical picture of the dielectric response function as a collection of interacting local responses that can be captured by a tight-binding model.« less

All-optically tunable EIT-like dielectric metasurfaces hybridized with thin phase change material layers

NASA Astrophysics Data System (ADS)

Petronijevic, Emilija; Sibilia, Concita

2017-05-01

Electromagnetically induced transparency (EIT), a pump-induced narrow transparency window within the absorption region of a probe, had offered new perspectives in slow-light control in atomic physics. For applications in nanophotonics, the implementation on chip-scaled devices has later been obtained by mimicking this effect by metallic metamaterials. High losses in visible and near infrared range of metal-based metamaterialls have recently opened a new field of all-dielectric metamaterials; a proper configuration of high refractive index dielectric nanoresonators can mimick this effect without losses to get high Q, slow-light response. The next step would be the ability to tune their optical response, and in this work we investigate thin layers of phase change materials (PCM) for all-optical control of EIT-like all-dielectric metamaterials. PCM can be nonvolatively and reversibly switched between two stable phases that differ in optical properties by applying a visible laser pulse. The device is based on Si nanoresonators covered by a thin layer of PCM GeTe; optical and transient thermal simulations have been done to find and optimize the fabrication parameters and switching parameters such as the intensity and duration of the pulse. We have found that the EIT-like response can be switched on and off by applying the 532nm laser pulse to change the phase of the upper GeTe layer. We strongly believe that such approach could open new perspectives in all-optically controlled slow-light metamaterials.

Annealing effect on the structural and dielectric properties of hematite nanoparticles

NASA Astrophysics Data System (ADS)

Kumar, Vijay; Chahal, Surjeet; Singh, Dharamvir; Kumar, Ashok; Kumar, Parmod; Asokan, K.

2018-05-01

In the present work, we have synthesized hematite (α-Fe2O3) nanoparticles by sol-gel method and sintered them at different temperatures (200 °C, 400 °C and 800 °C for six hours). The samples were then characterized using versatile characterization techniques such as X-ray diffraction (XRD), dielectric measurement and temperature dependent resistivity (RT) for their structural, dielectric and electrical properties. XRD measurements infer that intensity of peak increases with an increase in temperature resulting an increase in crystallite size. Temperature dependent resistivity also shows decrease in the resistivity of the samples. Furthermore, the dielectric measurements correspond to the increase in the dielectric constant. Based on these observations, it can be inferred that sintering temperature plays an important role in tailoring the various physical properties of hematite nanoparticles.

Analysis of terahertz dielectric properties of pork tissue

NASA Astrophysics Data System (ADS)

Huang, Yuqing; Xie, Qiaoling; Sun, Ping

2017-10-01

Seeing that about 70% component of fresh biological tissues is water, many scientists try to use water models to describe the dielectric properties of biological tissues. The classical water dielectric models are Debye model, Double Debye model and Cole-Cole model. This work aims to determine a suitable model by comparing three models above with experimental data. These models are applied to fresh pork tissue. By means of least square method, the parameters of different models are fitted with the experimental data. Comparing different models on both dielectric function, the Cole-Cole model is verified the best to describe the experiments of pork tissue. The correction factor α of the Cole-Cole model is an important modification for biological tissues. So Cole-Cole model is supposed to be a priority selection to describe the dielectric properties for biological tissues in the terahertz range.

Studies of ferroelectric and dielectric properties of pure and doped barium titanate prepared by sol-gel method

NASA Astrophysics Data System (ADS)

Bisen, Supriya; Mishra, Ashutosh; Jarabana, Kanaka M.

2016-05-01

In this work, Barium Titanate (BaTiO3) powders were synthesized via Sol-Gel auto combustion method using citric acid as a chelating agent. We study the behavior of ferroelectric and dielectric properties of pure and doped BaTiO3 on different concentration. To understand the phase and structure of the powder calcined at 900°C were characterized by X-ray Diffraction shows that tetragonal phase is dominant for pure and doped BTO and data fitted by Rietveld Refinement. Electric and Dielectric properties were characterized by P-E Hysteresis and Dielectric measurement. In P-E measurement ferroelectric loop tracer applied for different voltage. The temperature dependant dielectric constant behavior was observed as a function of frequency recorded on hp-Hewlett Packard 4192A, LF impedance, 5Hz-13Hz analyzer.

Ferroelectric and paraelectric Ba0.5Sr0.5TiO3 film structure distortions at room temperature and their effects on tunable microwave properties

NASA Astrophysics Data System (ADS)

Alldredge, L. M. B.; Chang, Wontae; Qadri, Syed B.; Kirchoefer, Steven W.; Pond, Jeffrey M.

2007-05-01

Sputter-deposited Ba0.5Sr0.5TiO3 films on (001) MgO were characterized for their dielectric properties with different lattice structures. With varying Ar :O2 ratios during deposition, the films showed either in-plane (ca) tetragonal distortions, significantly affecting the dielectric constant and tunability. The dielectric constant exhibited clear hysteresis with dc bias at room temperature, indicating that the films were ferroelectric. The relationship between the dielectric properties and the distortions was the reverse of that observed in films deposited by pulsed laser deposition. The anisotropic in-plane dielectric behavior can be understood by relating polarization to film distortions and to the presence of permanent dipoles.

Precise dielectric property measurements and E-field probe calibration for specific absorption rate measurements using a rectangular waveguide

PubMed Central

Hakim, B M; Beard, B B; Davis, C C

2018-01-01

Specific absorption rate (SAR) measurements require accurate calculations of the dielectric properties of tissue-equivalent liquids and associated calibration of E-field probes. We developed a precise tissue-equivalent dielectric measurement and E-field probe calibration system. The system consists of a rectangular waveguide, electric field probe, and data control and acquisition system. Dielectric properties are calculated using the field attenuation factor inside the tissue-equivalent liquid and power reflectance inside the waveguide at the air/dielectric-slab interface. Calibration factors were calculated using isotropicity measurements of the E-field probe. The frequencies used are 900 MHz and 1800 MHz. The uncertainties of the measured values are within ±3%, at the 95% confidence level. Using the same waveguide for dielectric measurements as well as calibrating E-field probes used in SAR assessments eliminates a source of uncertainty. Moreover, we clearly identified the system parameters that affect the overall uncertainty of the measurement system. PMID:29520129

Study of dielectric properties of adulterated milk concentration and freshness

NASA Astrophysics Data System (ADS)

Jitendra Murthy, V.; Sai Kiranmai, N.; Kumar, Sanjeev

2017-08-01

The knowledge of dielectric properties may hold a potential to develop a new technique for quality evaluation of milk. The dielectric properties of water diluted cow’s milk with milk concentration from 70 percent to 100 percent stored during 36hour storage at 22°C and 144 hour at 5°C were measured at room temperature for frequencies ranging from 10 to 4500 MHz and at low, high & at microwave frequencies using X band bench and open-ended coaxial-line probe technology, along with electrical conductivity. The raw milk had the lowest dielectric constant (ɛ‧) when the frequency was higher than about 20M.Hz, and had the highest loss (ɛ″) or decepation factor tan (δ) at each frequency. The penetration depth (dp) increased with decreasing frequency, water content and storage time, which was large enough to detect dielectric properties changes in milk samples and provide large scale RF pasteurization processes. The loss factor can be an indicator in predicting milk concentration and freshness.

Parameter Search Algorithms for Microwave Radar-Based Breast Imaging: Focal Quality Metrics as Fitness Functions.

PubMed

O'Loughlin, Declan; Oliveira, Bárbara L; Elahi, Muhammad Adnan; Glavin, Martin; Jones, Edward; Popović, Milica; O'Halloran, Martin

2017-12-06

Inaccurate estimation of average dielectric properties can have a tangible impact on microwave radar-based breast images. Despite this, recent patient imaging studies have used a fixed estimate although this is known to vary from patient to patient. Parameter search algorithms are a promising technique for estimating the average dielectric properties from the reconstructed microwave images themselves without additional hardware. In this work, qualities of accurately reconstructed images are identified from point spread functions. As the qualities of accurately reconstructed microwave images are similar to the qualities of focused microscopic and photographic images, this work proposes the use of focal quality metrics for average dielectric property estimation. The robustness of the parameter search is evaluated using experimental dielectrically heterogeneous phantoms on the three-dimensional volumetric image. Based on a very broad initial estimate of the average dielectric properties, this paper shows how these metrics can be used as suitable fitness functions in parameter search algorithms to reconstruct clear and focused microwave radar images.

Intrinsic and extrinsic dielectric responses of CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Rubinger, C. P. L.; Moreira, R. L.; Ribeiro, G. M.; Matinaga, F. M.; Autier Laurent, S.; Mercey, B.; Lobo, R. P. S. M.

2011-10-01

CaCu3Ti4O12 thin films were epitaxially grown on (001) LaAlO3 substrates by pulsed laser deposition under optimized growth conditions. The crystal structure and sample morphology were characterized by x-ray diffraction, AFM, TEM, ellipsometry, and Raman spectroscopy. The dielectric responses of the films were investigated in a large temperature range (5 to 375 K) by infrared reflectivity and impedance spectroscopies. The films exhibited a colossal dielectric response, with the dielectric permittivity reaching 104 at 100 Hz. The results obtained in a broad frequency range allowed us to investigate the behavior of intrinsic and extrinsic dielectric responses of this material. The room temperature centrosymmetrical cubic structure remains stable down to 5 K, though softening of the lower frequency infrared phonon modes indicates an incipient ferroelectric character. The radio frequency dielectric response reveals two relaxations of extrinsic origin, a primary higher frequency relaxation responsible for the colossal dielectric behavior and a secondary one of lower frequency. The activation energies of these processes are compatible with the presence of shallow defect levels created by oxygen vacancies.

Nonlinear dielectric properties of planar structures based on ferroelectric betaine phosphite films

NASA Astrophysics Data System (ADS)

Balashova, E. V.; Krichevtsov, B. B.; Svinarev, F. B.; Yurko, E. I.

2014-02-01

Ferroelectric films of partly deuterated betaine phosphite are grown on NdGaO3(001) substrates with an interdigitated system of electrodes on their surfaces by evaporation at room temperature. These films have a high capacitance in the ferroelectric phase transition range. The dielectric nonlinearity of the grown structures is studied in small-signal and strong-signal response modes and in the intermediate region between these two modes by measuring the capacitance in a dc bias field, dielectric hysteresis loops, and the Fourier spectra of an output signal in the Sawyer-Tower circuit. In the phase transition range, the capacitance control ratio at a bias voltage U bias = 40 V is K ≅ 7. The dielectric nonlinearity of the structures in the paraelectric phase is described by the Landau theory of second-order phase transitions. The additional contribution to the nonlinearity in the ferroelectric phase is related to the motion of domain walls and manifests itself when the input signal amplitude is higher than U st ˜ 0.7-1.0 V. The relaxation times of domain walls are determined from an analysis of the frequency dependences of the dielectric hysteresis.

Active Tuning of Spontaneous Emission by Mie-Resonant Dielectric Metasurfaces.

PubMed

Bohn, Justus; Bucher, Tobias; Chong, Katie E; Komar, Andrei; Choi, Duk-Yong; Neshev, Dragomir N; Kivshar, Yuri S; Pertsch, Thomas; Staude, Isabelle

2018-06-13

Mie-resonant dielectric metasurfaces offer comprehensive opportunities for the manipulation of light fields with high efficiency. Additionally, various strategies for the dynamic tuning of the optical response of such metasurfaces were demonstrated, making them important candidates for reconfigurable optical devices. However, dynamic control of the light-emission properties of active Mie-resonant dielectric metasurfaces by an external control parameter has not been demonstrated so far. Here, we experimentally demonstrate the dynamic tuning of spontaneous emission from a Mie-resonant dielectric metasurface that is situated on a fluorescent substrate and embedded into a liquid crystal cell. By switching the liquid crystal from the nematic state to the isotropic state via control of the cell temperature, we induce a shift of the spectral position of the metasurface resonances. This results in a change of the local photonic density of states, which, in turn, governs the enhancement of spontaneous emission from the substrate. Specifically, we observe spectral tuning of both the electric and magnetic dipole resonances, resulting in a 2-fold increase of the emission intensity at λ ≈ 900 nm. Our results demonstrate a viable strategy to realize flat tunable light sources based on dielectric metasurfaces.

Enhanced dielectric properties of poly(vinylidene fluoride) composites filled with nano iron oxide-deposited barium titanate hybrid particles

NASA Astrophysics Data System (ADS)

Zhang, Changhai; Chi, Qingguo; Dong, Jiufeng; Cui, Yang; Wang, Xuan; Liu, Lizhu; Lei, Qingquan

2016-09-01

We report enhancement of the dielectric permittivity of poly(vinylidene fluoride) (PVDF) generated by depositing magnetic iron oxide (Fe3O4) nanoparticles on the surface of barium titanate (BT) to fabricate BT-Fe3O4/PVDF composites. This process introduced an external magnetic field and the influences of external magnetic field on dielectric properties of composites were investigated systematically. The composites subjected to magnetic field treatment for 30 min at 60 °C exhibited the largest dielectric permittivity (385 at 100 Hz) when the BT-Fe3O4 concentration is approximately 33 vol.%. The BT-Fe3O4 suppressed the formation of a conducting path in the composite and induced low dielectric loss (0.3) and low conductivity (4.12 × 10-9 S/cm) in the composite. Series-parallel model suggested that the enhanced dielectric permittivity of BT-Fe3O4/PVDF composites should arise from the ultrahigh permittivity of BT-Fe3O4 hybrid particles. However, the experimental results of the BT-Fe3O4/PVDF composites treated by magnetic field agree with percolation theory, which indicates that the enhanced dielectric properties of the BT-Fe3O4/PVDF composites originate from the interfacial polarization induced by the external magnetic field. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry.

Enhanced dielectric properties of poly(vinylidene fluoride) composites filled with nano iron oxide-deposited barium titanate hybrid particles.

PubMed

Zhang, Changhai; Chi, Qingguo; Dong, Jiufeng; Cui, Yang; Wang, Xuan; Liu, Lizhu; Lei, Qingquan

2016-09-16

We report enhancement of the dielectric permittivity of poly(vinylidene fluoride) (PVDF) generated by depositing magnetic iron oxide (Fe3O4) nanoparticles on the surface of barium titanate (BT) to fabricate BT-Fe3O4/PVDF composites. This process introduced an external magnetic field and the influences of external magnetic field on dielectric properties of composites were investigated systematically. The composites subjected to magnetic field treatment for 30 min at 60 °C exhibited the largest dielectric permittivity (385 at 100 Hz) when the BT-Fe3O4 concentration is approximately 33 vol.%. The BT-Fe3O4 suppressed the formation of a conducting path in the composite and induced low dielectric loss (0.3) and low conductivity (4.12 × 10(-9) S/cm) in the composite. Series-parallel model suggested that the enhanced dielectric permittivity of BT-Fe3O4/PVDF composites should arise from the ultrahigh permittivity of BT-Fe3O4 hybrid particles. However, the experimental results of the BT-Fe3O4/PVDF composites treated by magnetic field agree with percolation theory, which indicates that the enhanced dielectric properties of the BT-Fe3O4/PVDF composites originate from the interfacial polarization induced by the external magnetic field. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry.

Enhanced dielectric properties of poly(vinylidene fluoride) composites filled with nano iron oxide-deposited barium titanate hybrid particles

PubMed Central

Zhang, Changhai; Chi, Qingguo; Dong, Jiufeng; Cui, Yang; Wang, Xuan; Liu, Lizhu; Lei, Qingquan

2016-01-01

We report enhancement of the dielectric permittivity of poly(vinylidene fluoride) (PVDF) generated by depositing magnetic iron oxide (Fe3O4) nanoparticles on the surface of barium titanate (BT) to fabricate BT–Fe3O4/PVDF composites. This process introduced an external magnetic field and the influences of external magnetic field on dielectric properties of composites were investigated systematically. The composites subjected to magnetic field treatment for 30 min at 60 °C exhibited the largest dielectric permittivity (385 at 100 Hz) when the BT–Fe3O4 concentration is approximately 33 vol.%. The BT–Fe3O4 suppressed the formation of a conducting path in the composite and induced low dielectric loss (0.3) and low conductivity (4.12 × 10−9 S/cm) in the composite. Series-parallel model suggested that the enhanced dielectric permittivity of BT–Fe3O4/PVDF composites should arise from the ultrahigh permittivity of BT–Fe3O4 hybrid particles. However, the experimental results of the BT–Fe3O4/PVDF composites treated by magnetic field agree with percolation theory, which indicates that the enhanced dielectric properties of the BT–Fe3O4/PVDF composites originate from the interfacial polarization induced by the external magnetic field. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry. PMID:27633958

Characterizations of biodegradable epoxy-coated cellulose nanofibrils (CNF) thin film for flexible microwave applications

Treesearch

Hongyi Mi; Chien-Hao Liu; Tzu-Husan Chang; Jung-Hun Seo; Huilong Zhang; Sang June Cho; Nader Behdad; Zhenqiang Ma; Chunhua Yao; Zhiyong Cai; Shaoqin Gong

2016-01-01

Wood pulp cellulose nanofibrils (CNF) thin film is a novel recyclable and biodegradable material. We investigated the microwave dielectric properties of the epoxy coated-CNF thin film for potential broad applications in flexible high speed electronics. The characterizations of dielectric properties were carried out in a frequency range of 1–10 GHz. The dielectric...

Microwave meter for rapid, nondestructive determination of in-shell peanut kernel moisture content from dielectric measurements on cleaned and uncleaned pod samples

USDA-ARS?s Scientific Manuscript database

Microwave Sensing provides a means for nondestructively determining the amount of moisture in materials by sensing the dielectric properties of the material. In this study, dielectric properties of Vidalia onions were analyzed for moisture dependence at 13.36 GHz and 23°C for moisture content betwee...

Method and Apparatus for Precisely Applying Large Planar Equi-Biaxial Strains to a Circular Membrane

DTIC Science & Technology

2013-04-01

potential future Army applications. Electronic properties, such as dielectric strength , capacitance, resistance, and inductance, vary significantly and... dielectric strength and resistance are primarily determined by inherent bulk material properties, including microstructure, while shifts in inductance...less and a nominal thickness up to ~1 mm. 15. SUBJECT TERMS large planar equi-biaxial strain, membrane, dielectric elastomers, electromechanical

Effects of TiO2 addition on microwave dielectric properties of Li2MgSiO4 ceramics

NASA Astrophysics Data System (ADS)

Rose, Aleena; Masin, B.; Sreemoolanadhan, H.; Ashok, K.; Vijayakumar, T.

2018-03-01

Silicates have been widely studied for substrate applications in microwave integrated circuits owing to their low dielectric constant and low tangent loss values. Li2MgSiO4 (LMS) ceramics are synthesized through solid-state reaction route using TiO2 as an additive to the pure ceramics. Variations in dielectric properties of LMS upon TiO2 addition in different weight percentages (0.5, 1.5, 2) are studied by keeping the sintering parameters constant. Crystalline structure, phase composition, and microstructure of LMS and LMS-TiO2 ceramics were studied using x-ray diffraction spectrometer and High Resolution Scanning electron microscope. Density was measured through Archimedes method and the microwave dielectric properties were examined by Cavity perturbation technique. LMS achieved relative permittivity (ε r) of 5.73 and dielectric loss (tan δ) of 5.897 × 10‑4 at 8 GHz. In LMS-TiO2 ceramics, 0.5 wt% TiO2 added LMS showed comparatively better dielectric properties than other weight percentages where ε r = 5.67, tan δ = 7.737 × 10‑4 at 8 GHz.

Effect of bromine deficiency on the lattice dynamics and dielectric properties of alpha-phase diisopropylammonium bromide molecular crystals

NASA Astrophysics Data System (ADS)

Alsaad, Ahmad; Marin, Chris M.; Alaqtash, Nabil; Chao, Hsien-Wen; Chang, Tsun-Hsu; Cheung, Chin Li; Ahmad, A.; Qattan, I. A.; Sabirianov, Renat F.

2018-02-01

Diisopropylammonium bromide (DIPAB) molecular ferroelectric crystals were synthesized and examined to exhibit a large electric polarization (∼23μC/cm2), a large dielectric constant in the α-phase. Although the PXRD pattern indicates that the α-DIPAB sample has an overall excellent crystallinity, our analysis of its FT-IR and Raman vibrational spectra suggests the presence of disorder in the synthesized crystals as indicated by the presence of broad features in the Raman spectrum. Using vdW+DF2 calculations, we identified the majority of vibrational modes in the experimental spectra and analyzed the ones due to Br-disorder. We found that the bromine (Br) deficiency strongly affects the electric properties of α-DIPAB. Particularly, the experimentally measured dielectric constant of α-DIPAB is large (∼20), whereas the DFT-based calculations of the ideal DIPAB give much smaller values (∼2-3). We find that Br-deficiency is responsible for large dielectric constant of the DIPAB crystal with calculated value of ∼15-20. Furthermore, we showed that the van der Waals forces have a slight effect on the structural parameters, only causing a small shift in the vibrational frequencies. The main vibrational features of the DIPAB crystal in the Raman spectrum were shown to be driven by covalent bonding in the DIPA molecules and hydrogen bonds between the molecules with Br.

High-k 3D-barium titanate foam/phenolphthalein poly(ether sulfone)/cyanate ester composites with frequency-stable dielectric properties and extremely low dielectric loss under reduced concentration of ceramics

NASA Astrophysics Data System (ADS)

Zheng, Longhui; Yuan, Li; Guan, Qingbao; Liang, Guozheng; Gu, Aijuan

2018-01-01

Higher dielectric constant, lower dielectric loss and better frequency stability have been the developing trends for high dielectric constant (high-k) materials. Herein, new composites have been developed through building unique structure by using hyperbranched polysiloxane modified 3D-barium titanate foam (BTF) (BTF@HSi) as the functional fillers and phenolphthalein poly(ether sulfone) (cPES)/cyanate ester (CE) blend as the resin matrix. For BTF@HSi/cPES/CE composite with 34.1 vol% BTF, its dielectric constant at 100 Hz is as high as 162 and dielectric loss is only 0.007; moreover, the dielectric properties of BTF@HSi/cPES/CE composites exhibit excellent frequency stability. To reveal the mechanism behind these attractive performances of BTF@HSi/cPES/CE composites, three kinds of composites (BTF/CE, BTF/cPES/CE, BTF@HSi/CE) were prepared, their structure and integrated performances were intensively investigated and compared with those of BTF@HSi/cPES/CE composites. Results show that the surface modification of BTF is good for preparing composites with improved thermal stability; while introducing flexible cPES to CE is beneficial to fabricate composites with good quality through effectively blocking cracks caused by the stress concentration, and then endowing the composites with good dielectric properties at reduced concentration of ceramics.

Effect of La3+ Substitution on Electric, Dielectric and Magnetic Properties of Cobalt Nano-Ferrite

NASA Astrophysics Data System (ADS)

Kumar, Pawan; Singh, M.

2011-07-01

Ultrafine particles of CoLaxFe2-xO4 (x = 0, 0.20) were prepared by using co-precipitation method. X-ray diffraction studies show that the samples have cubic spinel structure and average crystallite size of x = 0 and x = 0.2 are 49.84 nm and 27.73 nm respectively. Dielectric and magnetic properties have been studied by impedance analyzer and magnetic properties of the ferrite system were studied using VSM respectively. La3+ ions modulate significantly the electric, dielectric and magnetic properties of cobalt spinel ferrites.

Transport properties of lithium ions doped vanado-bismuth-tellurite glasses

NASA Astrophysics Data System (ADS)

Keshavamurthy, K.; Eraiah, B.

2016-05-01

The glasses of composition (65-x)V2O5-xLi2O-20TeO2-15Bi2O3 (x = 15 and 25 mol%) were prepared by conventional melt quenching method and their electrical conductivity and dielectric measurements have been carried out in the frequency range 40Hz to 6MHz over a temperature 373 to 473 K. The conductivity values increased with both Li2O concentration and temperature. Interestingly, the dielectric response showed the existence of a negative capacitance effect in the present glass system and concluded that this effect arose from the presence of external inductive reactance.

Preparation and Electrical Properties of La0.9Sr0.1TiO3+δ

PubMed Central

Li, Wenzhi; Ma, Zhuang; Gao, Lihong; Wang, Fuchi

2015-01-01

La1−xSrxTiO3+δ (LST) has been studied in many fields, especially in the field of microelectronics due to its excellent electrical performance. Our previous theoretical simulated work has suggested that LST has good dielectric properties, but there are rare reports about this, especially experimental reports. In this paper, LST was prepared using a solid-state reaction method. The X-rays diffraction (XRD), scanning electron microscope (SEM), broadband dielectric spectroscopy, impedance spectroscopy and photoconductive measurement were used to characterize the sample. The results show that the values of dielectric parameters (the relative dielectric constant εr and dielectric loss tanδ), dependent on temperature, are stable under 350 °C and the value of the relative dielectric constant and dielectric loss are about 52–88 and 6.5 × 10−3, respectively. Its value of conductivity increases with rise in temperature, which suggests its negative temperature coefficient of the resistance. In addition, the band gap of LST is about 3.39 eV, so it belongs to a kind of wide-band-gap semiconductor materials. All these indicate that LST has anti-interference ability and good dielectric properties. It could have potential applications as an electronic material. PMID:28787995

Dielectric properties of biomass and biochar mixtures for bioenergy applications

USDA-ARS?s Scientific Manuscript database

Biomass is an abundant and renewable energy resource, which may be converted into energy-dense products through thermochemical processes such as pyrolysis and gasification. Since microwave heating depends on the dielectric properties of the biomass material, these properties were measured at freque...

Ferroelectric properties of Pb(Zr,Ti)O3 films under ion-beam induced strain

NASA Astrophysics Data System (ADS)

Lee, Jung-Kun; Nastasi, Michael

2012-11-01

The influence of an ion-beam induced biaxial stress on the ferroelectric and dielectric properties of Pb(Zr,Ti)O3 (PZT) films is investigated using the ion beam process as a novel approach to control external stress. Tensile stress is observed to decrease the polarization, permittivity, and ferroelectric fatigue resistance of the PZT films whose structure is monoclinic. However, a compressive stress increases all of them in monoclinic PZT films. The dependence of the permittivity on stress is found not to follow the phenomenological theory relating external forces to intrinsic properties of ferroelectric materials. Changes in the ferroelectric and dielectric properties indicate that the application of a biaxial stress modulates both extrinsic and intrinsic properties of PZT films. Different degrees of dielectric non-linearity suggests the density and mobility of non-180o domain walls, and the domain switching can be controlled by an applied biaxial stress and thereby influence the ferroelectric and dielectric properties.

Effects of La2O3-B2O3-ZnO additions on the low temperature sintering and microwave dielectric properties of (Ca0.61La0.26) TiO3 ceramics

NASA Astrophysics Data System (ADS)

Chen, Y. W.; Li, E. Z.; Niu, N.; Zou, M. Y.; Duan, S. X.; Zhang, S. R.

2017-02-01

The influence of La2O3-B2O3-ZnO (LBZ) additions on the sintering behavior, microstructure, phase composition, and the microwave dielectric properties of (Ca0.61La0.26) TiO3 (CLT) ceramics have been investigated. The results indicate that the LBZ additions could efficiently lower the sintering temperature of the CLT ceramics from 1400°C to 950°C, and excellent microwave properties remain. Small amount of LBZ glass promotes the densification of the CLT ceramics and enhances the microwave dielectric properties. However, excess amount of LBZ glass deteriorates the dielectric properties because of the increasing glass phase. The CLT ceramic with 3 wt. % LBZ additions, sintered at 950°C, exhibit excellent properties: εr= 103.12, Q× f = 8826 GHz(f=3.312 GHz) and τƒ=299.52 ppm/°C.

Nondestructive defect detection in laser optical coatings

NASA Astrophysics Data System (ADS)

Marrs, C. D.; Porteus, J. O.; Palmer, J. R.

1985-03-01

Defects responsible for laser damage in visible-wavelength mirrors are observed at nondamaging intensities using a new video microscope system. Studies suggest that a defect scattering phenomenon combined with lag characteristics of video cameras makes this possible. Properties of the video-imaged light are described for multilayer dielectric coatings and diamond-turned metals.

Boron nitride as two dimensional dielectric: Reliability and dielectric breakdown

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, Yanfeng; Pan, Chengbin; Hui, Fei

2016-01-04

Boron Nitride (BN) is a two dimensional insulator with excellent chemical, thermal, mechanical, and optical properties, which make it especially attractive for logic device applications. Nevertheless, its insulating properties and reliability as a dielectric material have never been analyzed in-depth. Here, we present the first thorough characterization of BN as dielectric film using nanoscale and device level experiments complementing with theoretical study. Our results reveal that BN is extremely stable against voltage stress, and it does not show the reliability problems related to conventional dielectrics like HfO{sub 2}, such as charge trapping and detrapping, stress induced leakage current, and untimelymore » dielectric breakdown. Moreover, we observe a unique layer-by-layer dielectric breakdown, both at the nanoscale and device level. These findings may be of interest for many materials scientists and could open a new pathway towards two dimensional logic device applications.« less

Dielectric properties of lanthanum gallate (LaGaO3) crystal

NASA Astrophysics Data System (ADS)

Dube, D. C.; Scheel, H. J.; Reaney, I.; Daglish, M.; Setter, N.

1994-04-01

Dielectric properties of single crystals of LaGaO3 have been measured at low frequencies as well as in the microwave region over a wide temperature range. Measurements performed on two crystal orientations, viz. (001) and (110), show dielectric anomalies at a transition near 145 °C. Dielectric anisotropy below, but not above, 145 °C confirm the previously reported orthorhombic symmetry at room temperature and rhombohedral symmetry above 145 °C. Domain wall motion which arises as a result of a phase transition has been observed around 145 °C.

First-principles investigation of band offsets and dielectric properties of Silicon-Silicon Nitride interfaces

NASA Astrophysics Data System (ADS)

Pham, Tuan Anh; Li, Tianshu; Gygi, Francois; Galli, Giulia

2011-03-01

Silicon Nitride (Si3N4) is a possible candidate material to replace or be alloyed with SiO2 to form high-K dielectric films on Si substrates, so as to help prevent leakage currents in modern CMOS transistors. Building on our previous work on dielectric properties of crystalline and amorphous Si3N4 slabs, we present an analysis of the band offsets and dielectric properties of crystalline-Si/amorphous Si3N4 interfaces based on first principles calculations. We discuss shortcomings of the conventional bulk-plus line up approach in band offset calculations for systems with an amorphous component, and we present the results of band offsets obtained from calculations of local density of states. Finally, we describe the role of bonding configurations in determining band edges and dielectric constants at the interface. We acknowledge financial support from Intel Corporation.

Large dielectric permittivity and possible correlation between magnetic and dielectric properties in bulk BaFeO{sub 3−δ}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagdeo, Archna; Gautam, Kamini; Singh, M. N.

2014-07-28

We report structural, magnetic, and dielectric properties of oxygen deficient hexagonal BaFeO{sub 3−δ}. A large dielectric permittivity comparable to that of other semiconducting oxides is observed in BaFeO{sub 3−δ}. Magnetization measurements indicate magnetic inhomogeneity and the system shows a paramagnetic to antiferromagnetic transition at ∼160 K. Remarkably, the temperature, at which paramagnetic to antiferromagnetic transition occurs, around this temperature, a huge drop in the dissipation factor takes place and resistivity shoots up; this indicates the possible correlation among magnetic and dielectric properties. First principle simulations reveal that some of these behaviors may be explained in terms of many body electron correlationmore » effect in the presence of oxygen vacancy present in BaFeO{sub 3−δ} indicating its importance in both fundamental science as well as in applications.« less

Dielectric and electrical properties of binary mixtures of 1-butyl-3-methylimadazolium and water in the frequency range 20 Hz to 2 MHz

NASA Astrophysics Data System (ADS)

Barot, D. K.; Chaube, H. A.; Rana, V. A.

2017-05-01

The complex relative dielectric function ɛ*(ω) = ɛ'-jɛ″ of binary mixture of 1-Butyl-3-methylimadazolium (BMiCl) with water of varying concentration have been measured using Precision LCR meter in the frequency range 20 Hz to 2 MHz at 293.15 K. The dielectric and electrical properties of BMiCl and water are represented in terms of electrical conductivity σ*(ω) and complex relative dielectric function ɛ*(ω). To describe the relationship of the electrical conductivity with concentration, the empirical Casteel-Amis (C-A) equation was used. The influence of concentration variation of BMiCl in water to the various electrical parameters was discussed. All of these presentations are used to explore various processes contributed in the electrical/dielectric properties of the mixtures of BMiCl and water.

Dielectric properties of inorganic fillers filled epoxy thin film

NASA Astrophysics Data System (ADS)

Norshamira, A.; Mariatti, M.

2015-07-01

The demand on the small size and high performance electronics has driven changes in the electronic packaging requirements from discrete capacitor to embedded capacitor. Embedded capacitor can improve electrical performance compared with discrete capacitor. This study aimed to achieve high dielectric of epoxy thin film composite that were targeted for application as embedded capacitor. In this study, inorganic fillers such as Calcium Copper Titanate (CCTO), Iron(III) Oxide (Fe2O3) and Titanium Dioxide (TiO2) were loaded in epoxy system at 5 and 20vol%. Morphology and dielectric properties were investigated to identify the effect of fillers loading and types of fillers on the properties of epoxy thin film composite. Based on the study, CCTO with 20vol% loading was found to have good dielectric properties compared to other type of fillers.

Dielectric properties of single wall carbon nanotubes-based gelatin phantoms

NASA Astrophysics Data System (ADS)

Altarawneh, M. M.; Alharazneh, G. A.; Al-Madanat, O. Y.

In this work, we report the dielectric properties of Single wall Carbon Nanotubes (SWCNTs)-based phantom that is mainly composed of gelatin and water. The fabricated gelatin-based phantom with desired dielectric properties was fabricated and doped with different concentrations of SWCNTs (e.g., 0%, 0.05%, 0.10%, 0.15%, 0.2%, 0.4% and 0.6%). The dielectric constants (real ɛ‧ and imaginary ɛ‧‧) were measured at different positions for each sample as a function of frequency (0.5-20GHz) and concentrations of SWCNTs and their averages were found. The Cole-Cole plot (ɛ‧ versus ɛ‧‧) was obtained for each concentration of SWCNTs and was used to obtain the static dielectric constant ɛs, the dielectric constant at the high limit of frequency ɛ∞ and the average relaxation time τ. The measurements showed that the fabricated samples are in good homogeneity and the SWCNTs are dispersed well in the samples as an acceptable standard deviation is achieved. The study showed a linear increase in the static dielectric constant ɛs and invariance of the average relaxation time τ and the value of ɛ∞ at room temperature for the investigated concentrations of SWCNTs.

Properties of multilayer filters

NASA Technical Reports Server (NTRS)

Baumeister, P. W.

1973-01-01

New methods were investigated of using optical interference coatings to produce bandpass filters for the spectral region 110 nm to 200 nm. The types of filter are: triple cavity metal dielectric filters; all dielectric reflection filters; and all dielectric Fabry Perot type filters. The latter two types use thorium fluoride and either cryolite films or magnesium fluoride films in the stacks. The optical properties of the thorium fluoride were also measured.

Linear and nonlinear optical properties of α-K2Hg3Ge2S8 and α-K2Hg3Sn2S8 compounds

NASA Astrophysics Data System (ADS)

Reshak, A. H.; Azam, Sikander

2014-11-01

The linear and nonlinear optical properties of α-K2Hg3Ge2S8 and α-K2Hg3Sn2S8 compounds are performed using the first-principles calculations. Particularly, we appraised the optical dielectric function and the second-harmonic generation (SHG) response. We have analyzed the linear optical properties, i.e. the real and imaginary part of the dielectric tensor, the reflectivity, refractive index, extension coefficient and energy loss function. The linear optical properties show a considerable anisotropy which is important for SHG as it is defined by the phase-matching condition. The scrutiny of the roles of diverse transitions to the SHG coefficients demonstrates that the virtual electron process is foremost. The features in the spectra of χ322(2)(ω) are successfully interrelated with the character of the linear dielectric function ε(ω) in terms of single-photon and two-photon resonances. In additional, we have calculated the first hyperpolarizability, βijk, for the dominant component at the static limit for the for α-K2Hg3Ge2S8 and α-K2Hg3Sn2S8 compounds. The calculated values of β322(ω) are 2.28 × 10-30 esu for α-K2Hg3Ge2S8 and 3.69 × 10-30 esu for α-K2Hg3Sn2S8.

Defect Complex Effect in Nb Doped TiO2 Ceramics with Colossal Permittivity

NASA Astrophysics Data System (ADS)

Li, Fuchao; Shang, Baoqiang; Liang, Pengfei; Wei, Lingling; Yang, Zupei

2016-10-01

Donor-doped Nb x Ti1- x O2 ( x = 1%, 2%, 4%, 6%, and 8%) ceramics with giant permittivity (>104) and a very low dielectric loss (˜0.05) were sintered under flowing N2 at 1400°C for 10 h. By increasing Nb doping concentration, two different dielectric responses were evidenced in the frequency dependence of dielectric properties of Nb doped TiO2 ceramics, which corresponded to the space charge polarization and the electron-pinned defect-dipoles effect, respectively. Especially, combined with the x-ray photoelectron spectroscopy results, the electron-pinned defect-dipoles induced by the 2({Nb}^{5 + } )_{{Ti}}^{ bullet } to 4({Ti}^{3 + } )^'_{{Ti}} leftarrow {V}_{{o}}^{ bullet bullet } defect complex were further confirmed to give rise to both their high ɛr and low tan δ in the high frequency range for the Nb x Ti1- x O2 ceramics with x > 4%.

The Current State of Silicone-Based Dielectric Elastomer Transducers.

PubMed

Madsen, Frederikke B; Daugaard, Anders E; Hvilsted, Søren; Skov, Anne L

2016-03-01

Silicone elastomers are promising materials for dielectric elastomer transducers (DETs) due to their superior properties such as high efficiency, reliability and fast response times. DETs consist of thin elastomer films sandwiched between compliant electrodes, and they constitute an interesting class of transducer due to their inherent lightweight and potentially large strains. For the field to progress towards industrial implementation, a leap in material development is required, specifically targeting longer lifetime and higher energy densities to provide more efficient transduction at lower driving voltages. In this review, the current state of silicone elastomers for DETs is summarised and critically discussed, including commercial elastomers, composites, polymer blends, grafted elastomers and complex network structures. For future developments in the field it is essential that all aspects of the elastomer are taken into account, namely dielectric losses, lifetime and the very often ignored polymer network integrity and stability. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of interface point defect on the dielectric properties of Y doped CaCu3Ti4O12 ceramics

NASA Astrophysics Data System (ADS)

Deng, Jianming; Sun, Xiaojun; Liu, Saisai; Liu, Laijun; Yan, Tianxiang; Fang, Liang; Elouadi, Brahim

2016-04-01

CaCu3Ti4-xYxO12 (0≤x≤0.12) ceramics were fabricated with conventional solid-state reaction method. Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The impedance and modulus tests both suggested the existence of two different relaxation behavior, which were attributed to bulk and grain boundary response. In addition, the conductivity and dielectric permittivity showed a step-like behavior under 405K. Meanwhile, frequency independence of dc conduction became dominant when above 405K. In CCTO ceramic, rare earth element Y3+ ions as an acceptor were used to substitute Ti sites, decreasing the concentration of oxygen vacancy around grain-electrode and grain boundary. The reason to the reduction of dielectric behavior in low frequencies range was associated with the Y doping in CCTO ceramic.

Recent advances in characterization of CaCu3Ti4O12 thin films by spectroscopic ellipsometric metrology.

PubMed

Lo Nigro, Raffaella; Malandrino, Graziella; Toro, Roberta G; Losurdo, Maria; Bruno, Giovanni; Fragalà, Ignazio L

2005-10-12

CaCu3Ti4O12 (CCTO) thin films were successfully grown on LaAlO3(100) and Pt/TiO2/SiO2/Si(100) substrates by a novel MOCVD approach. Epitaxial CCTO(001) thin films have been obtained on LaAlO3(100) substrates, while polycrystalline CCTO films have been grown on Pt/TiO2/SiO2/Si(100) substrates. Surface morphology and grain size of the different nanostructured deposited films were examined by AFM, and spectroscopic ellipsometry has been used to investigate the electronic part of the dielectric constant (epsilon2). Looking at the epsilon2 curves, it can be seen that by increasing the film structural order, a greater dielectric response has been obtained. The measured dielectric properties accounted for the ratio between grain volumes and grain boundary areas, which is very different in the different structured films.

High-pressure endurable flexible tactile actuator based on microstructured dielectric elastomer

NASA Astrophysics Data System (ADS)

Pyo, Dongbum; Ryu, Semin; Kyung, Ki-Uk; Yun, Sungryul; Kwon, Dong-Soo

2018-02-01

We demonstrate a robust flexible tactile actuator that is capable of working under high external pressures. The tactile actuator is based on a pyramidal microstructured dielectric elastomer layer inducing variation in both mechanical and dielectric properties. The vibrational performance of the actuator can be modulated by changing the geometric parameter of the microstructures. We evaluated the performance of the actuator under high-pressure loads up to 25 kPa, which is over the typical range of pressure applied when humans touch or manipulate objects. Due to the benefit of nonlinearity of the pyramidal structure, the actuator could maintain high mechanical output under various external pressures in the frequency range of 100-200 Hz, which is the most sensitive to vibration acceleration for human finger pads. The responses are not only fast, reversible, and highly durable under consecutive cyclic operations, but also large enough to impart perceivable vibrations for haptic feedback on practical wearable device applications.

Influence of the local structure in phase-change materials on their dielectric permittivity.

PubMed

Shportko, Kostiantyn V; Venger, Eugen F

2015-01-01

Ge-Sb-Te alloys, which belong to the phase-change materials, are promising materials for data storage and display and data visualization applications due to their unique properties. This includes a remarkable difference of their electrical and optical properties in the amorphous and crystalline state. Pronounced change of optical properties for Ge-Sb-Te alloys is linked to the different bonding types and different atomic arrangements in amorphous and crystalline states. The dielectric function of phase-change materials has been investigated in the far infrared (FIR) range. Phonons have been detected by FTIR spectroscopy. Difference of the dispersion of the dielectric permittivity of amorphous and crystalline samples is caused by different structures in different states which contribute to the dielectric permittivity.

Optical properties of graphene, silicene, germanene, and stanene from IR to far UV - A first principles study

NASA Astrophysics Data System (ADS)

John, Rita; Merlin, Benita

2017-11-01

This study offers an analysis of optical properties of Graphene and its 2D analogues: Silicene, Germanene, and Stanene with the help of band structures based on Density Functional Theory. The complex dielectric function and complex refractive index are calculated in both parallel (||) and perpendicular (⊥) polarization directions of the electromagnetic field. From these calculated values, optical observables like absorption, reflection, optical conductivity, and electron loss function have been studied. The optical response of all materials is shifted from ultraviolet (UV) to infrared (IR) from graphene to stanene; Graphene is more into UV region and other materials in the IR and visible regions. The intensity of absorption is maximum for stanene. The real part of dielectric function reveals the existence of plasma frequency in the || polarization direction indicating the metal to dielectric transition except for graphene. Study on refractive index clearly displays the birefringence characteristics of all materials. Reflectivity is enhanced in the mid IR and visible regions when light is polarized in the || direction. The in-depth investigations arrive at fine results which would enable the prediction of their potential applications in the optical and optoelectronic industries.

Structural, dielectric and gas sensing behavior of Mn substituted spinel MFe2O4 (M=Zn, Cu, Ni, and Co) ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Ranjith Kumar, E.; Siva Prasada Reddy, P.; Sarala Devi, G.; Sathiyaraj, S.

2016-01-01

Spinel ferrite (MnZnFe2O4, MnCuFe2O4, MnNiFe2O4 and MnCoFe2O4) nanoparticles have been prepared by evaporation method. The annealing temperature plays an important role on changing particle size of the spinel ferrite nanoparticles was found out by X-ray diffraction and transmission electron microscopy. The role of manganese substitution in the spinel ferrite nanoparticles were also analyzed for different annealing temperature. The substitution of Mn also creates a vital change in dielectric properties have been measured in the frequency range of 100 kHz to 5 MHz. These spinel ferrites are decomposed to α-Fe2O3 after annealing above 550 °C in air. Through the characterization of the prepared powder, the effect of annealing temperature, chemical composition and preparation technique on the microstructure, particle size and dielectric properties of the Mn substituted spinel ferrite nanoparticles are discussed. Furthermore, Conductance response of Mn substituted MFe2O4 ferrite nanoparticles were measured by exposing the materials to reducing gas like liquefied petroleum gas (LPG).

Colossal dielectric and electromechanical responses in self-assembled polymeric nanocomposites

NASA Astrophysics Data System (ADS)

Huang, Cheng; Zhang, Q. M.; Li, Jiang Yu; Rabeony, Manese

2005-10-01

An electroactive polymer nanocomposite, in which high dielectric constant copper phthalocyanine oligomer (o-CuPc) nanoparticles are incorporated into the block polyurethane (PU) matrix by the combination of "top down" and "bottom up" approaches, was realized. Such an approach enables the nanocomposite to exhibit colossal dielectric and electromechanical responses with very low volume fraction of the high dielectric constant o-CuPc nanofillers (˜3.5%) in the composite. In contrast, a simple blend of o-CuPc and PU composite with much higher o-CuPc content (˜16% of o-CuPc) shows much lower dielectric and electromechanical responses.

Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells.

PubMed

Juarez-Perez, Emilio J; Sanchez, Rafael S; Badia, Laura; Garcia-Belmonte, Germá; Kang, Yong Soo; Mora-Sero, Ivan; Bisquert, Juan

2014-07-03

Organic-inorganic lead trihalide perovskites have emerged as an outstanding photovoltaic material that demonstrated a high 17.9% conversion efficiency of sunlight to electricity in a short time. We have found a giant dielectric constant (GDC) phenomenon in these materials consisting on a low frequency dielectric constant in the dark of the order of ε0 = 1000. We also found an unprecedented behavior in which ε0 further increases under illumination or by charge injection at applied bias. We observe that ε0 increases nearly linearly with the illumination intensity up to an additional factor 1000 under 1 sun. Measurement of a variety of samples of different morphologies, compositions, and different types of contacts shows that the GDC is an intrinsic property of MAPbX3 (MA = CH3NH3(+)). We hypothesize that the large dielectric response is induced by structural fluctuations. Photoinduced carriers modify the local unit cell equilibrium and change the polarizability, assisted by the freedom of rotation of MA. The study opens a way for the understanding of a key aspect of the photovoltaic operation of high efficiency perovskite solar cells.

Electromagnetic response of dielectric nanostructures in liquid crystals

NASA Astrophysics Data System (ADS)

Amanaganti, S.; Chowdhury, D. R.; Ravnik, M.; Dontabhaktuni, J.

2018-02-01

Sub-wavelength periodic metallic nanostructures give rise to very interesting optical phenomena like effective refractive index, perfect absorption, cloaking, etc. However, such metallic structures result in high dissipative losses and hence dielectric nanostructures are being considered increasingly to be an efficient alternative to plasmonic materials. High refractive index (RI) dielectric nanostructures exhibit magnetic and electric resonances simultaneously giving rise to interesting properties like perfect magnetic mirrors, etc. In the present work, we study light-matter interaction of cubic dielectric structures made of very high refractive index material Te in air. We observe a distinct band-like structure in both transmission and reflection spectra resulting from the interaction between magnetic and electric dipolar modes. FDTD simulations using CST software are performed to analyse the different modes excited at the band frequencies. The medium when replaced with liquid crystal gives rise to asymmetry in the band structure emphasizing one of the dominant magnetic modes at resonance frequencies. This will help in achieving a greater control on the excitation of the predominant magnetic dipolar modes at resonance frequencies with applications as perfect magnetic mirrors.

Synthesis, structural, characterization and dielectric spectroscopy of PVDF - BaTiO3 polymer composite

NASA Astrophysics Data System (ADS)

Kulkarni, S. S.; Belavi, P. B.; Khadke, U. V.

2018-05-01

In this paper we report the method of synthesis of ferroelectric polymer Polyvinyldene fluoride (PVDF) and Barium Titanate (BaTiO3) composite self supporting thin films and its dielectric response. BaTiO3 was synthesized by solid state reaction method. The PVDF - BaTiO3 polymer composites with various concentrations were synthesized by solution mixing method using Dimethylformadide (DMF) as a solvent. The phase transformation and surface methodology of the prepared composites were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) respectively. The XRD pattern confirms the formation of tetragonal pervoskite structure of ferroelectric phase. The XRD pattern shows the proper mixing of BaTiO3 particles intestinally and found to be improving its crystallinity with increase of BaTiO3 composition in the PVDF matrix. The dielectric properties of the composites as a function of frequency were computed using impedance analyzer. The dielectric constant decreases with increase of frequency shows the Maxwell - Wagner type of interfacial polarization in accordance with Koop's phenomenological theory.

Plasmonic modes and extinction properties of a random nanocomposite cylinder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moradi, Afshin, E-mail: a.moradi@kut.ac.ir

We study the properties of surface plasmon-polariton waves of a random metal-dielectric nanocomposite cylinder, consisting of bulk metal embedded with dielectric nanoparticles. We use the Maxwell-Garnett formulation to model the effective dielectric function of the composite medium and show that there exist two surface mode bands. We investigate the extinction properties of the system, and obtain the dependence of the extinction spectrum on the nanoparticles’ shape and concentration as well as the cylinder radius and the incidence angle for both TE and TM polarization.

Stress hysteresis and mechanical properties of plasma-enhanced chemical vapor deposited dielectric films

NASA Astrophysics Data System (ADS)

Thurn, Jeremy; Cook, Robert F.; Kamarajugadda, Mallika; Bozeman, Steven P.; Stearns, Laura C.

2004-02-01

A comprehensive survey is described of the responses of three plasma-enhanced chemical vapor deposited dielectric film systems to thermal cycling and indentation contact. All three films—silicon oxide, silicon nitride, and silicon oxy-nitride—exhibited significant nonequilibrium permanent changes in film stress on thermal cycling or annealing. The linear relationship between stress and temperature changed after the films were annealed at 300 °C, representing a structural alteration in the film reflecting a change in coefficient of thermal expansion or biaxial modulus. A double-substrate method was used to deduce both thermoelastic properties before and after the anneal of selected films and the results were compared with the modulus deconvoluted from small-scale depth-sensing indentation experiments (nanoindentation). Rutherford backscattering spectrometry and hydrogen forward scattering were used to deduce the composition of the films and it was found that all the films contained significant amounts of hydrogen.

Rietveld refinement, dielectric and magnetic properties of Nb modified Bi0.80Ba0.20FeO3 ceramic

NASA Astrophysics Data System (ADS)

Jangra, Sandhaya; Sanghi, Sujata; Agarwal, Ashish; Rangi, Manisha

2018-05-01

Bi0.80Ba0.20Fe0.95Nb0.05O3 ceramic has been prepared via conventional solid state reaction method. Structure analysis was carried out by X-ray diffraction (XRD) technique at room temperature. XRD pattern confirmed the crystalline nature of prepared sample. Rietveld analysis used for further structural investigations and confirmed the existence of rhombohedral symmetry (R3c space group). The dielectric response shows dispersion at lower frequency range and becomes frequency independent at high frequency. The approximation of conduction mechanism is determined by the temperature dependent behavior of frequency exponent `s'. Fitting results suggests the applicability of small polaron conduction mechanism at lower temperatures and CBH model at higher temperature. Room temperature magnetic measurements give the evidence of significant enhancement in magnetic properties with remanent magnetization (Mr = 0.1218 emu/g) and coercive field (Hc = 3.5342 kOe).

Interactions of light with rough dielectric surfaces - Spectral reflectance and polarimetric properties

NASA Technical Reports Server (NTRS)

Yon, S. A.; Pieters, C. M.

1988-01-01

The nature of the interactions of visible and NIR radiation with the surfaces of rock and mineral samples was investigated by measuring the reflectance and the polarization properties of scattered and reflected light for slab samples of obsidian and fine-grained basalt, prepared to controlled surface roughness. It is shown that the degree to which radiation can penetrate a surface and then scatter back out, an essential criterion for mineralogic determinations based on reflectance spectra, depends not only upon the composition of the material, but also on its physical condition such as sample grain size and surface roughness. Comparison of the experimentally measured reflectance and polarization from smooth and rough slab materials with the predicted models indicates that single Fresnel reflections are responsible for the largest part of the reflected intensity resulting from interactions with the surfaces of dielectric materials; multiple Fresnel reflections are much less important for such surfaces.

The dielectric signature of glass density

NASA Astrophysics Data System (ADS)

Rams-Baron, M.; Wojnarowska, Z.; Knapik-Kowalczuk, J.; Jurkiewicz, K.; Burian, A.; Wojtyniak, M.; Pionteck, J.; Jaworska, M.; Rodríguez-Tinoco, C.; Paluch, M.

2017-09-01

At present, we are witnessing a renewed interest in the properties of densified glasses prepared by isobaric cooling of a liquid at elevated pressure. As high-pressure densification emerges as a promising approach in the development of glasses with customized features, understanding and controlling their unique properties represent a contemporary scientific and technological goal. The results presented herein indicate that the applied high-pressure preparation route leads to a glassy state with higher density (˜1%) and a reduced free volume of about 7%. We show that these subtle structural changes remarkably influence the dielectric response and spectral features of β-relaxation in etoricoxib glass. Our study, combining dynamical and structural techniques, reveal that β-relaxation in etoricoxib is extremely sensitive to the variations in molecular packing and can be used to probe the changes in glass density. Such connection is technologically relevant and may advance further progress in the field.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Fei; Zhang, Shujun; Yang, Tiannan

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric propertiesmore » is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.« less

Mechanical, dielectric, and physicochemical properties of impregnating resin based on unsaturated polyesterimides

NASA Astrophysics Data System (ADS)

Fetouhi, Louiza; Petitgas, Benoit; Dantras, Eric; Martinez-Vega, Juan

2017-10-01

This work aims to characterize the dielectric and the mechanical properties of a resin based on an unsaturated polyesterimide diluted in methacrylate reactive diluents used in the impregnation of rotating machines. The broadband dielectric spectrometry and the dynamic mechanical analysis were used to quantify the changes in dielectric and mechanical properties of the network PEI resin, as a function of temperature and frequency. The network characterizations highlight the presence of two main relaxations, α and α', confirmed by the differential scanning calorimetry analysis, showing the complexity of the chemical composition of this resin. The dielectric spectroscopy shows a significant increase in the dielectric values due to an increase of the material conductivity, while the mechanical spectroscopy shows an important decrease of the polymer rigidity and viscosity expressed by an important decrease in the storage modulus. The PEI resin shows a high reactivity when it is submitted in successive heating ramps, which involves in a post-cross-linking reaction. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2016)", edited by Adel Razek

Ultra-Wideband Millimeter-Wave Dielectric Characteristics of Freshly Excised Normal and Malignant Human Skin Tissues.

PubMed

Mirbeik-Sabzevari, Amir; Ashinoff, Robin; Tavassolian, Negar

2018-06-01

Millimeter waves have recently gained attention for the evaluation of skin lesions and the detection of skin tumors. Such evaluations heavily rely on the dielectric contrasts existing between normal and malignant skin tissues at millimeter-wave frequencies. However, current studies on the dielectric properties of normal and diseased skin tissues at these frequencies are limited and inconsistent. In this study, a comprehensive dielectric spectroscopy study is conducted for the first time to characterize the ultra-wideband dielectric properties of freshly excised normal and malignant skin tissues obtained from skin cancer patients having undergone Mohs micrographic surgeries at Hackensack University Medical Center. Measurements are conducted using a precision slim-form open-ended coaxial probe in conjunction with a millimeter-wave vector network analyzer over the frequency range of 0.5-50 GHz. A one-pole Cole-Cole model is fitted to the complex permittivity dataset of each sample. Statistically considerable contrasts are observed between the dielectric properties of malignant and normal skin tissues over the ultra-wideband millimeter-wave frequency range considered.

Effect of soil texture on the microwave emission from soils

NASA Technical Reports Server (NTRS)

Schmugge, T. J.

1980-01-01

The intensity brightness temperature of the microwave emission from the soil is determined primarily by its dielectric properties. The large difference between the dielectric constant of water and that of dry soil produces a strong dependence of the soil's dielectric constant on its moisture content. This dependence is effected by the texture of the soil because the water molecules close to the particle surface are tightly bound and do not contribute significantly to the dielectric properties. Since this surface area is a function of the particle size distribution (soil texture), being larger for clay soils with small particles, and smaller for sandy soils with larger particles; the dielectric properties will depend on soil texture. Laboratory measurements of the dielectric constant for soils are summarized. The dependence of the microwave emission on texture is demonstrated by measurements of brightness temperature from an aircraft platform for a wide range of soil textures. It is concluded that the effect of soil texture differences on the observed values can be normalized by expressing the soil moisture values as a percent field capacity for the soil.

Temperature dependent optical properties of ZnO thin film using ellipsometry and photoluminescence

NASA Astrophysics Data System (ADS)

Bouzourâa, M.-B.; Battie, Y.; Dalmasso, S.; Zaïbi, M.-A.; Oueslati, M.; En Naciri, A.

2018-05-01

We report the temperature dependence of the dielectric function, the exciton binding energy and the electronic transitions of crystallized ZnO thin film using spectroscopic ellipsometry (SE) and photoluminescence (PL). ZnO layers were prepared by sol-gel method and deposited on crystalline silicon (Si) by spin coating technique. The ZnO optical properties were determined between 300 K and 620 K. Rigorous study of optical responses was achieved in order to demonstrate the quenching exciton of ZnO as a function of temperature. Numerical technique named constrained cubic splines approximation (CCS), Tauc-Lorentz (TL) and Tanguy dispersion models were selected for the ellipsometry data modeling in order to obtain the dielectric function of ZnO. The results reveals that the exciton bound becomes widely flattening at 470 K on the one hand, and on the other that the Tanguy dispersion law is more appropriate for determining the optical responses of ZnO thin film in the temperature range of 300 K-420 K. The Tauc-Lorentz, for its part, reproduces correctly the ZnO dielectric function in 470 K-620 K temperature range. The temperature dependence of the electronic transition given by SE and PL shows that the exciton quenching was observed in 420 K-∼520 K temperature range. This quenching effect can be explained by the equilibrium between the Coulomb force of exciton and its kinetic energy in the film. The kinetic energy was found to induce three degrees of freedom of the exciton.

A comparative study of the properties of five-layered Aurivillius oxides A2Bi4Ti5O18 (A = Ba, Pb, and Sr) synthesized by different wet chemical routes

NASA Astrophysics Data System (ADS)

Dubey, Shivangi; Subohi, Oroosa; Kurchania, Rajnish

2018-07-01

This paper reports the detailed study of the effect of different wet chemical synthesis routes (solution combustion, co-precipitation, and sol-gel route) on the microstructure, phase formation, dielectric, electrical, and ferroelectric properties of five-layered Aurivillius oxides: A2Bi4Ti5O18 (A = Ba, Pb, and Sr). Different synthesis parameters like the precursors used, synthesis temperature, and reaction time affects the morphology of the ceramics. Microstructure in turn influences the dielectric and ferroelectric properties. It was observed that the sol-gel-synthesized ceramics possess higher dielectric constant and remanent polarization, low dielectric loss due to lower conductivity in these samples as a result of higher density in these compounds as compared to those synthesized by other wet chemical synthesis routes such as solution combustion route and co-precipitation technique. The XRD data are used for phase analysis and surface morphology is studied using SEM images. Dielectric and electrical properties are investigated as a function of frequency and temperature.

Dielectric properties of dog brain tissue measured in vitro across the 0.3-3 GHz band.

PubMed

Mohammed, Beadaa; Bialkowski, Konstanty; Abbosh, Amin; Mills, Paul C; Bradley, Andrew P

2016-09-22

Dielectric properties of dead Greyhound female dogs' brain tissues at different ages were measured at room temperature across the frequency range of 0.3-3 GHz. Measurements were made on excised tissues, in vitro in the laboratory, to carry out dielectric tests on sample tissues. Each dataset for a brain tissue was parametrized using the Cole-Cole expression, and the relevant Cole-Cole parameters for four tissue types are provided. A comparison was made with the database available in literature for other animals and human brain tissue. Results of two types of tissues (white matter and skull) showed systematic variation in dielectric properties as a function of animal age, whereas no significant change related to age was noticed for other tissues. Results provide critical information regarding dielectric properties of animal tissues for a realistic animal head model that can be used to verify the validity and reliability of a microwave head scanner for animals prior to testing on live animals. Bioelectromagnetics. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Preparation, Structural and Dielectric Properties of Solution Grown Polyvinyl Alcohol(PVA) Film

NASA Astrophysics Data System (ADS)

Nangia, Rakhi; Shukla, Neeraj K.; Sharma, Ambika

2017-08-01

Flexible dielectrics with high permittivity have been investigated extensively due to their applications in electronic industry. In this work, structural and electrical characteristics of polymer based film have been analysed. Poly vinyl alcohol (PVA) film was prepared by solution casting method. X-ray diffraction (XRD) characterization technique is used to investigate the structural properties. The semi-crystalline nature has been determined by the analysis of the obtained XRD pattern. Electrical properties of the synthesized film have been analysed from the C-V and I-V curves obtained at various frequencies and temperatures. Low conductivity values confirm the insulating behaviour of the film. However, it is found that conductivity increases with temperature. Also, the dielectric permittivity is found to be higher at lower frequencies and higher temperatures, that proves PVA to be an excellent dielectric material which can be used in interface electronics. Dielectric behaviour of the film has been explained based on dipole orientations to slow and fast varying electric field. However further engineering can be done to modulate the structural, electrical properties of the film.

Effect of ultrasound dielectric pretreatment on the oxidation resistance of vacuum-fried apple chips.

PubMed

Shen, Xu; Zhang, Min; Bhandari, Bhesh; Guo, Zhimei

2018-02-15

In order to investigate the effect of ultrasound dielectric pretreatment on the oxidation resistance of vacuum-fried apple chips, apple slices were pretreated at ultrasonic powers of 150, 250 and 400 W for times of 10, 20 and 30 min before vacuum frying. The quality and oxidation resistance of fried apple were evaluated by testing the dielectric properties and comparing the moisture content, oil uptake, color, acid value (AV) and peroxide value (PV) of apple chips. Ultrasonic treatment significantly changed the dielectric properties of apple slices. Moisture and oil contents of apple chips decreased with increasing ultrasonic power and time. During storage, the color retention of fried apple chips processed by ultrasound was improved. AV and PV values of fried apple chips processed by ultrasound were lower, which improved their antioxidant properties. The results of the present study indicated that ultrasound dielectric pretreatment improved not only the quality of vacuum-fried apple chips but also their antioxidant properties. © 2018 Society of Chemical Industry. © 2018 Society of Chemical Industry.

Elastic properties of porous low-k dielectric nano-films

NASA Astrophysics Data System (ADS)

Zhou, W.; Bailey, S.; Sooryakumar, R.; King, S.; Xu, G.; Mays, E.; Ege, C.; Bielefeld, J.

2011-08-01

Low-k dielectrics have predominantly replaced silicon dioxide as the interlayer dielectric for interconnects in state of the art integrated circuits. In order to further reduce interconnect RC delays, additional reductions in k for these low-k materials are being pursued via the introduction of controlled levels of porosity. The main challenge for such dielectrics is the substantial reduction in elastic properties that accompanies the increased pore volume. We report on Brillouin light scattering measurements used to determine the elastic properties of these films at thicknesses well below 200 nm, which are pertinent to their introduction into present ultralarge scale integrated technology. The observation of longitudinal and transverse standing wave acoustic resonances and their transformation into traveling waves with finite in-plane wave vectors provides for a direct non-destructive measure of the principal elastic constants that characterize the elastic properties of these porous nano-scale films. The mode dispersion further confirms that for porosity levels of up to 25%, the reduction in the dielectric constant does not result in severe degradation in the Young's modulus and Poisson's ratio of the films.

Dynamic Structure Factor: An Introduction

NASA Astrophysics Data System (ADS)

Sturm, K.

1993-02-01

The doubly differential cross-section for weak inelastic scattering of waves or particles by manybody systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system. The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-particle response function in self-consistent field approximations, such as the random-phase approximation or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function.

Structure-property relations in sputter deposited epitaxial (1-x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 thin films

NASA Astrophysics Data System (ADS)

Frederick, Joshua C.

Lead-based ferroelectric materials are of significant technological importance for sensing and actuation due to their high piezoelectric performance (i.e., the ability to convert an electrical signal to mechanical displacement, and vice versa). Traditionally, bulk ceramic or single crystals materials have filled these roles; however, emerging technologies stand to benefit by incorporating thin films to achieve miniaturization while maintaining high efficiency and sensitivity. Currently, chemical systems that have been well characterized in bulk form (e.g. Pb(Mg1/3Nb2/3)O3- xPbTiO3, or PMN-xPT) require further study to optimize both the chemistry and structure for deployment in thin film devices. Furthermore, the effect of internal electric fields is more significant at the length scales of thin films, resulting in self biases that require compensation to reveal their intrinsic dielectric response. To this end, the structure-property relations of epitaxial PMN-xPT films sputter deposited on a variety of substrates were investigated. Attention was paid to how the structure (i.e., strain state, crystal structure, domain configuration, and defects) gave rise to the ferroelectric, dielectric, and piezoelectric response. Three-dimensional visualization of the dielectric response as a simultaneous function of electric field and temperature revealed the true phase transition of the films, which was found to correspond to the strain state and defect concentration. A lead-buffered anneal process was implemented to enhance the ferroelectric and dielectric response of the films without altering their stoichiometry. It was discovered that PMN- xPT films could be domain-engineered to exhibit a mixed domain state through chemistry and substrate choice. Such films exhibited a monoclinic distortion similar to that of the bulk compositions near the morphotropic phase boundary. Finally, it was revealed that the piezoelectric response could be greatly enhanced by declamping the film from the substrate via a membrane fabrication technique. The membrane structures exhibited enhanced domain wall mobility, suggesting that domain wall motion is crucial for strong piezoelectric performance in PMN-xPT films. The findings can help guide strain- and domain-engineered relaxor ferroelectric thin films tailored for particular applications.

Influence of Al3+ substitution on the electrical resistivity and dielectric behavior of Ni0.25Cu0.20Zn0.55AlxFe2-xO4 ferrites synthesized by solid state reaction technique

NASA Astrophysics Data System (ADS)

Rahman, K. R.; Chowdhury, F.-U.-Z.; Khan, M. N. I.

2017-12-01

In this paper, the effect of Al3+ substitution on the electrical and dielectric properties of Ni0.25Cu0.20Zn0.55AlxFe2-xO4 ferrites with x = 0.0, 0.05. 0.10, 0.15 and 0.20, synthesized by solid state reaction has been reported. Using two probe method, the DC resistivity has been investigated in the temperature range from 30 °C to 300 °C. Activation energy was calculated from the Arrhenius plot. The electrical conduction is explained on the basis of the hopping mechanism. The frequency dependent dielectric properties of these spinel ferrites have been studied at room temperature by measuring AC resistivity, conductivity (σac), dielectric constant and dielectric loss tangent (tan δ) in the frequency range between 1 kHz and 120 MHz. The study of dielectric properties showed that the dielectric constant and dielectric loss increased with increasing non-magnetic Al ions. The dependence of dielectric constant with frequency has been explained by Maxwell-Wagner interfacial polarization. Cole-Cole plots show semicircular arc(s) for the samples, and equivalent RC circuits have been proposed to clarify the phenomena involved therein. The analysis of complex impedance spectroscopy has been used to distinguish between the grain and grain boundary contribution to the total resistance.

Nonlinear electroelastic deformations of dielectric elastomer composites: II - Non-Gaussian elastic dielectrics

NASA Astrophysics Data System (ADS)

Lefèvre, Victor; Lopez-Pamies, Oscar

2017-02-01

This paper presents an analytical framework to construct approximate homogenization solutions for the macroscopic elastic dielectric response - under finite deformations and finite electric fields - of dielectric elastomer composites with two-phase isotropic particulate microstructures. The central idea consists in employing the homogenization solution derived in Part I of this work for ideal elastic dielectric composites within the context of a nonlinear comparison medium method - this is derived as an extension of the comparison medium method of Lopez-Pamies et al. (2013) in nonlinear elastostatics to the coupled realm of nonlinear electroelastostatics - to generate in turn a corresponding solution for composite materials with non-ideal elastic dielectric constituents. Complementary to this analytical framework, a hybrid finite-element formulation to construct homogenization solutions numerically (in three dimensions) is also presented. The proposed analytical framework is utilized to work out a general approximate homogenization solution for non-Gaussian dielectric elastomers filled with nonlinear elastic dielectric particles that may exhibit polarization saturation. The solution applies to arbitrary (non-percolative) isotropic distributions of filler particles. By construction, it is exact in the limit of small deformations and moderate electric fields. For finite deformations and finite electric fields, its accuracy is demonstrated by means of direct comparisons with finite-element solutions. Aimed at gaining physical insight into the extreme enhancement in electrostriction properties displayed by emerging dielectric elastomer composites, various cases wherein the filler particles are of poly- and mono-disperse sizes and exhibit different types of elastic dielectric behavior are discussed in detail. Contrary to an initial conjecture in the literature, it is found (inter alia) that the isotropic addition of a small volume fraction of stiff (semi-)conducting/high-permittivity particles to dielectric elastomers does not lead to the extreme electrostriction enhancements observed in experiments. It is posited that such extreme enhancements are the manifestation of interphasial phenomena.

Instability and efficiency of mixed halide perovskites CH 3NH 3AI 3-xCl x (A = Pb and Sn): A first-principles, computational study

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Yuping; Galli, Giulia

Here, we carried out calculations based on density functional theory to investigate the electronic, vibrational, and dielectric properties of mixed halide perovskites CH 3NH 3AI 3–xCl x with A = Pb and Sn. Computed free energies indicated that Cl mixed systems may be formed only for Cl concentrations not exceeding 10 19 cm –3, and phonon calculations showed that the disorder induced in the host lattice by the presence of a smaller halogen is responsible for mechanical instabilities. However, we found that the presence of chloride may be beneficial to the electronic properties of the perovskites. Chloride anions cause themore » organic cations to be displaced from the center of the cage; such a displacement induces preferential orientations of the cation dipole, which in turn are responsible for notable changes in the dielectric properties of the material and possibly for the formation of local ferroelectric domains. The latter are instrumental in separating electron hole pairs and hence in contributing to long charge-carrier diffusion lengths, in spite of polarons being more likely formed in mixed perovksites than in CH 3NH 3AI 3.« less

Instability and efficiency of mixed halide perovskites CH 3NH 3AI 3-xCl x (A = Pb and Sn): A first-principles, computational study

DOE PAGES

He, Yuping; Galli, Giulia

2016-12-14

Here, we carried out calculations based on density functional theory to investigate the electronic, vibrational, and dielectric properties of mixed halide perovskites CH 3NH 3AI 3–xCl x with A = Pb and Sn. Computed free energies indicated that Cl mixed systems may be formed only for Cl concentrations not exceeding 10 19 cm –3, and phonon calculations showed that the disorder induced in the host lattice by the presence of a smaller halogen is responsible for mechanical instabilities. However, we found that the presence of chloride may be beneficial to the electronic properties of the perovskites. Chloride anions cause themore » organic cations to be displaced from the center of the cage; such a displacement induces preferential orientations of the cation dipole, which in turn are responsible for notable changes in the dielectric properties of the material and possibly for the formation of local ferroelectric domains. The latter are instrumental in separating electron hole pairs and hence in contributing to long charge-carrier diffusion lengths, in spite of polarons being more likely formed in mixed perovksites than in CH 3NH 3AI 3.« less

Preparation and Dielectric Measurements of the Rare Earth Green Phases R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb)

NASA Technical Reports Server (NTRS)

Gonzalez-Titman, Carlos

1994-01-01

It has been demonstrated that R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb) does not undergo significant densification unless the sintering temperatures are near the incongruent melting point or the sintering times are long. Good quality powders of Y2BaCuO(5-x) have been synthesized by using oxide raw materials or precursors such as acetates and nitrates. The acetates- and the nitrates-derived yttrium green phase resulted in finer particle sizes, acceptable dielectric properties and lower melting temperatures than those processed via oxide raw materials. The hot pressing technique has been employed to produce a dense R2BaCuO(5-x) (R=Y,Gd) substrate with satisfactory dielectric properties. Reactivity to reducing conditions, i.e. graphite die, limited the optimization of the properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO,.,,. Oxygen treatment at 950 OC has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO(5-x). Oxygen treatment at 950 C has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. The dielectric constants of the rare earth green phases R2BaCuO(5-x) were found to be low. Relaxation peaks were detected at low temperatures (T less than 150 K) and at high temperatures (150 less than T greater than 420 K). The dielectric losses and conductivities at 77 K were measured to be in the range of 10(exp -4) and 10(exp -12) (Omega-cm)(exp -1), respectively. Many parameters were found to exhibit dependencies on the rare earth cation sizes.

Dielectric and structural characterisation of chalcogenide glasses via terahertz time-domain spectroscopy

NASA Astrophysics Data System (ADS)

Ravagli, A.; Naftaly, M.; Craig, C.; Weatherby, E.; Hewak, D. W.

2017-07-01

Terahertz time-domain spectroscopy (THz TDS) was used to investigate a series of chalcogenide glasses. In particular, the dielectric properties at terahertz frequencies were determined and correlated with the glass composition. The experimental results showed a strong relationship between the dielectric properties and the polarizability of the glasses studied. A new explanation based on the coordination number of the metallic cations was proposed to understand these observations.

All-optical tuning of EIT-like dielectric metasurfaces by means of chalcogenide phase change materials.

PubMed

Petronijevic, E; Sibilia, C

2016-12-26

Electromagnetically induced transparency (EIT) is a pump-induced narrowband transparency window within an absorption line of the probe beam spectrum in an atomic system. In this paper we propose a way to bring together the all-dielectric metamaterials to have EIT-like effects and to optically tune the response by hybridizing them with a layer of a phase change material. We propose a design of the metamaterial based on Si nanoresonators that can support an EIT-like resonant response. On the top of the resonators we consider a thin layer of a chalcogenide phase change material, which we will use to tune the optical response. Our choice is Ge₂Sb₂Te₅ (GST), since it has two stable phases at room temperature, namely amorphous and crystalline, between which it can be switched quickly, nonvolatively and reversibly, sustaining a large number of switching cycles. They differ in optical properties, while still having moderately low losses in telecom range. Since such dielectric resonators do not have non-radiative losses of metals around 1550nm, they can lead to a high-Q factor of the EIT-like response in this range. Firstly, we optimize the starting structure so that it gives an EIT-like response at 1550 nm when the GST layer is in the amorphous state. Our starting design uses glass as a substrate, but we also consider implementation in SOI technology. If we then switch the thin layer of GST to its crystalline phase, which has higher losses, the EIT-like response is red shifted, providing around 10:1 contrast at 1550nm. This reversible tuning can be done with an ns visible pulsed laser. We discuss the results of the simulation of the dielectric metasurface for different configurations and the tuning possibility.

Frequency and temperature dependence of dielectric and ac electrical properties of NiFe2O4-ZnO multiferroic nanocomposite

NASA Astrophysics Data System (ADS)

Dutta, Papia; Mandal, S. K.; Dey, P.; Nath, A.

2018-04-01

We have presented the ac electrical properties and dielectric studies of 0.5 NiFe2O4 - 0.5 ZnO multiferroic nanocomposites prepared through low temperature "pyrophoric reaction process". Structural characterization has been carried out through X-ray diffraction technique, which shows the co-existence of both the phases of the nanocomposites. The ac electrical properties of nanocomposites have been studied employing impedance spectroscopy technique. The impedance value is found to increase with increase in magnetic field attributing the magnetostriction property of the composites. Dielectric constant is found to decrease with both the increase in magnetic fields and temperatures. Studies of dielectric constant reveal the Maxwell Wagner interfacial polarization at low frequency regime. Relaxation frequency as a function of magnetic fields and temperatures is found to shift towards the high frequency region.

Fabrication and properties of SiNO continuous fiber reinforced BN wave-transparent composites

NASA Astrophysics Data System (ADS)

Cao, F.; Fang, Z.; Chen, F.; Shen, Q.; Zhang, C.

2012-06-01

SiNO continuous fiber reinforced boron nitride (BN) wave-transparent composites (SiNO f /BN) have been fabricated by a precursor infiltration pyrolysis (PIP) method using borazine as the precursor. The densification behavior, microstructures, mechanical properties, and dielectric properties of the composites have been investigated. After four PIP cycles, the density of the composites had increased from 1.1 g·cm-3 to 1.81 g·cm-3. A flexural strength of 128.9 MPa and an elastic modulus of 23.5 GPa were achieved. The obtained composites have relatively high density and the fracture faces show distinct fiber pull-out and interface de-bonding features. The dielectric properties of the SiNO f /BN composites, including the dielectric constant of 3.61 and the dielectric loss angle tangent of 5.7×10-3, are excellent for application as wave-transparent materials.

Dielectric properties of inorganic fillers filled epoxy thin film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norshamira, A., E-mail: myra.arshad@gmail.com; Mariatti, M., E-mail: mariatti@usm.my

2015-07-22

The demand on the small size and high performance electronics has driven changes in the electronic packaging requirements from discrete capacitor to embedded capacitor. Embedded capacitor can improve electrical performance compared with discrete capacitor. This study aimed to achieve high dielectric of epoxy thin film composite that were targeted for application as embedded capacitor. In this study, inorganic fillers such as Calcium Copper Titanate (CCTO), Iron(III) Oxide (Fe{sub 2}O{sub 3}) and Titanium Dioxide (TiO{sub 2}) were loaded in epoxy system at 5 and 20vol%. Morphology and dielectric properties were investigated to identify the effect of fillers loading and types ofmore » fillers on the properties of epoxy thin film composite. Based on the study, CCTO with 20vol% loading was found to have good dielectric properties compared to other type of fillers.« less

Optically-Induced Magnetic Response in All-Dielectric Nanodisk Composite Structures

NASA Astrophysics Data System (ADS)

Chong, Katie Eve

Optical technologies developed throughout history have been exploiting the electric response in matters in order to control light. However, little has been explored for the magnetic response in matter at optical frequencies due to the lack of magnetic materials in this spectral region. Recently, specially engineered materials, namely metamaterials, have been developed to exploit the magnetic responses in matter for light manipulation. In particular, researchers have made use of the optically-induced magnetic responses (OIMRs) generated in metallic nanostructures to achieve optical effects not seen in nature. Such magnetic responses serve as a second channel to control light, providing an alternative and an addition to the electric responses and leading to novel observations and innovative ideas for light manipulation. This creates many opportunities for the development of the next generation nano-optics and nanophotonic devices. Dielectric nanostructures have recently been discovered to also support OIMR, which is useful for applications requiring low loss and simpler fabrication procedures, such as wavefront control and robust nanoscale sensing. In this thesis, I present the study of OIMR in several all-dielectric systems based on silicon nanodisks, namely single, clusters and regular arrays of nanodisks. The study of these systems provides knowledge for and insight into harnessing the OIMRs in dielectric nanostructures for future applications. Chapter 1 provides a comprehensive introduction to OIMR by presenting a historic overview of the topic and the basic concepts involved for high-index dielectric particles. This is followed by a description of the pioneer works on OIMR in dielectric spherical nanoparticles, including the Mie theory and its recent experimental verification. The similarities and differences between the properties of plasmonic and dielectric nanostructures in the context of metamaterials are also described and explained. Finally, the motivation and scope of the thesis is summarized. Chapter 2 describes the experimental methods used that are common to all works presented in this thesis, including the fabrication of silicon nanodisk structures and the linear optical characterization techniques. Chapter 3 presents the fundamental of OIMR in single silicon nanodisk structures, including a theoretical analysis and experimental observation of various resonant modes of single silicon nanodisks, as well as the numerical and experimental results of the Fano resonances observed in the more complex structures of single heptamer oligomers. Chapter 4 focuses on manipulating the OIMR in combination with the electric response to create Huygens' metasurfaces based on silicon nanodisk arrays. Two highly-efficient functional metadevices with polarization independence based on the Huygens' metasurface system are presented, namely a Gaussian-to-vortex beam shaper and a holographic phase plate. Chapter 5 explores the cross-disciplinary area of sensing using silicon nanodisk arrays with OIMRs, including refractive index sensing using Fano resonances and biosensing using the dipolar magnetic resonances where a new detection limit for the Streptavidin protein was achieved. Chapter 6 concludes the thesis and provides an outlook to the research works that can be extended from the results in this thesis.

Titanium dioxide thin films deposited by pulsed laser deposition and integration in radio frequency devices: Study of structure, optical and dielectric properties

NASA Astrophysics Data System (ADS)

Orlianges, Jean-Christophe; Crunteanu, Aurelian; Pothier, Arnaud; Merle-Mejean, Therese; Blondy, Pierre; Champeaux, Corinne

2012-12-01

Titanium dioxide presents a wide range of technological application possibilities due to its dielectric, electrochemical, photocatalytic and optical properties. The three TiO2 allotropic forms: anatase, rutile and brookite are also interesting, since they exhibit different properties, stabilities and growth modes. For instance, rutile has a high dielectric permittivity, of particular interest for the integration as dielectric in components such as microelectromechanical systems (MEMS) for radio frequency (RF) devices. In this study, titanium dioxide thin films are deposited by pulsed laser deposition. Characterizations by Raman spectroscopy and X-ray diffraction show the evolution of the structural properties. Thin films optical properties are investigated using spectroscopic ellipsometry and transmission measurements from UV to IR range. Co-planar waveguide (CPW) devices are fabricated based on these films. Their performances are measured in the RF domain and compared to simulation, leading to relative permittivity values in the range 30-120, showing the potentialities of the deposited material for capacitive switches applications.

Low-loss Ca{sub 5-x}Sr{sub x}A{sub 2}TiO{sub 12} [A=Nb,Ta] ceramics: Microwave dielectric properties and vibrational spectroscopic analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bijumon, Pazhoor Varghese; Sebastian, Mailadil Thomas; Dias, Anderson

2005-05-15

Complex perovskite-type Ca{sub 5-x}Sr{sub x}A{sub 2}TiO{sub 12} [A=Nb,Ta] (0{<=}x{<=}5) ceramics were prepared by conventional solid-state ceramic route. The crystal structure, microwave dielectric properties, and vibrational spectroscopic characteristics of these materials are reported. The structure and microstructure were investigated by x-ray diffraction and scanning electron microscopy techniques. The microwave dielectric properties were measured in the 3-5-GHz frequency range by the resonance method. Structural evolutions from orthorhombic to an averaged pseudocubic phase, with associated changes in dielectric properties, were observed as a function of composition. The structure-property relationships in these ceramics were established using Raman and Fourier transform infrared spectroscopic techniques. Ramanmore » analysis showed characteristic bands of ordered perovskite materials, with variation in both intensity and frequency as a function of composition.« less

Role of defects and oxygen vacancies on dielectric and magnetic properties of Pb2+ ion doped LaFeO3 polycrystalline ceramics

NASA Astrophysics Data System (ADS)

Devi Chandrasekhar, K.; Mallesh, S.; Krishna Murthy, J.; Das, A. K.; Venimadhav, A.

2014-09-01

We have presented the dielectric/impedance spectroscopy of La1-xPbxFeO3 (x=0.15 and 0.25) polycrystalline samples in a wide temperature and frequency range. They exhibited colossal dielectric permittivity and multiple relaxations. Temperature and field dependent magnetization study showed enhancement of magnetization upon Pb doping which has been ascribed to the defect driven magnetization phenomenon. Overall we have emphasized the formation of various kinds of defects and their influence on dielectric and magnetic properties in the system.

Structural, optical and dielectric properties of graphene oxide

NASA Astrophysics Data System (ADS)

Bhargava, Richa; Khan, Shakeel

2018-05-01

The Modified Hummers method has been used to synthesize Graphene oxide nanoparticles. Microstructural analyses were carried out by X-ray diffraction and Fourier transform infrared spectroscopy. Optical properties were studied by UV-visible spectroscopy in the range of 200-700 nm. The energy band gap was calculated with the help of Tauc relation. The frequency dependence of dielectric constant and dielectric loss were studied over a range of the frequency 75Hz to 5MHz at room temperature. The dispersion in dielectric constant can be explained with the help of Maxwell-Wagner model in studied nanoparticles.

Oxygen vacancy effect on dielectric and hysteretic properties of zigzag ferroelectric iron dioxide nanoribbon

NASA Astrophysics Data System (ADS)

Zriouel, S.; Taychour, B.; Yahyaoui, F. El; Drissi, L. B.

2017-07-01

Zigzag FeO2 nanoribbon defected by the removal of oxygen atoms is simulated using Monte Carlo simulations. All possible arrangements of positions and number of oxygen vacancy are investigated. Temperature dependence of polarization, dielectric susceptibility, internal energy, specific heat and dielectric hysteresis loops are all studied. Results show the presence of second order phase transition and Q - type behavior. Dielectric properties dependence on ribbon's edge, positions and number of oxygen vacancy are discussed in detail. Moreover, single and square hysteresis loops are observed whatever the number of oxygen vacancy in the system.

Effects of rare earth ionic doping on microstructures and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Renzhong; Department of Technology and Physics, Zhengzhou University of Light Industry, Zhengzhou 450002; Chen, Zhenping, E-mail: xrzbotao@163.com

2015-06-15

Graphical abstract: The dielectric constant decreases monotonically with reduced RE doping ion radius and is more frequency independent compared with that of pure CCTO sample. - Highlights: • The mean grain sizes decrease monotonically with reduced RE doping ionic radius. • Doping gives rise to the monotonic decrease of ϵ{sub r} with reduced RE ionic radius. • The nonlinear coefficient and breakdown field increase with RE ionic doping. • α of all the samples is associated with the potential barrier width rather than Φ{sub b}. - Abstract: Ca{sub 1–x}R{sub x}Cu{sub 3}Ti{sub 4}O{sub 12}(R = La, Nd, Eu, Gd, Er; xmore » = 0 and 0.005) ceramics were prepared by the conventional solid-state method. The influences of rare earth (RE) ion doping on the microstructure, dielectric and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics were investigated systematically. Single-phase formation is confirmed by XRD analyses. The mean grain size decreases monotonically with reduced RE ion radius. The EDS results reveal that RE ionic doping reduces Cu-rich phase segregation at the grain boundaries (GBs). Doping gives rise to the monotonic decrease of dielectric constant with reduced RE ionic radius but significantly improves stability with frequency. The lower dielectric loss of doped samples is obtained due to the increase of GB resistance. In addition, the nonlinear coefficient and breakdown field increase with RE ionic doping. Both the fine grains and the enhancement of potential barrier at GBs are responsible for the improvement of the nonlinear current–voltage properties in doped CCTO samples.« less

Microstructure and electrical properties of CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, S. F.; Zhang, J. L.; Zheng, P.

2006-04-15

CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics are prepared by the conventional solid-state reaction method under various sintering temperatures from 1000 to 1120 deg. C at an interval of 10 deg. C. Microstructures and crystalline structures are examined by scanning electronic microscopy and x-ray diffraction, respectively. Dielectric properties and complex impedances are investigated within the frequency range of 40 Hz-110 MHz over the temperature region from room temperature to 350 deg. C. It has been disclosed that the microstructures can be categorized into three different types: type A (with the small but uniform grain sizes), type B (with the bimodal distributionmore » of grain sizes) and type C (with the large and uniform grain sizes), respectively. The largeness of low-frequency dielectric permittivity at room temperature is closely related to the microstructure. Ceramics with different types of microstructures show the diverse temperature-dependent behaviors of electrical properties. However, the existence of some common characteristics is also found among them. For all of the ceramics, a Debye-type relaxation emerges in the frequency range of 100 Hz-100 kHz at high measuring temperatures, which has the larger dielectric dispersion strength than the one known in the frequency range above 100 kHz. Thus, the high-temperature dielectric dispersion exhibits a large low-frequency response and two Debye-type relaxations. Furthermore, all of the ceramics show three semicircles in the complex impedance plane. These semicircles are considered to represent individually different electrical mechanisms, among which the one in the low-frequency range arises most probably from the contribution of the domain boundaries, and the other two are ascribed to the contributions of the domains and the grain boundaries, respectively.« less

Dielectric response properties of parabolically-confined nanostructures in a quantizing magnetic field

NASA Astrophysics Data System (ADS)

Sabeeh, Kashif

This thesis presents theoretical studies of dielectric response properties of parabolically-confined nanostructures in a magnetic field. We have determined the retarded Schrodinger Green's function for an electron in such a parabolically confined system in the presence of a time dependent electric field and an ambient magnetic field. Following an operator equation of motion approach developed by Schwinger, we calculate the result in closed form in terms of elementary functions in direct-time representation. From the retarded Schrodinger Green's function we construct the closed-form thermodynamic Green's function for a parabolically confined quantum-dot in a magnetic field to determine its plasmon spectrum. Due to confinement and Landau quantization this system is fully quantized, with an infinite number of collective modes. The RPA integral equation for the inverse dielectric function is solved using Fredholm theory in the nondegenerate and quantum limit to determine the frequencies with which the plasmons participate in response to excitation by an external potential. We exhibit results for the variation of plasmon frequency as a function of magnetic field strength and of confinement frequency. A calculation of the van der Waals interaction energy between two harmonically confined quantum dots is discussed in terms of the dipole-dipole correlation function. The results are presented as a function of confinement strength and distance between the dots. We also rederive a result of Fertig & Halperin [32] for the tunneling-scattering of an electron through a saddle potential which is also known as a quantum point contact (QPC), in the presence of a magnetic field. Using the retarded Green's function we confirm the result for the transmission coefficient and analyze it.

Effect of Bi doping on morphotropic phase boundary and dielectric properties of PZT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joshi, Shraddha; Acharya, Smita, E-mail: saha275@yahoo.com

2016-05-23

In our present attempt, Pb{sub (1-x)}Bi{sub x}Zr{sub 0.52}Ti{sub 0.48}O{sub 3} [PBZT] {where x = 0, 0.05, 0.1} is synthesized by sol-gel route. Effect of Bi addition on structure, sinterability and dielectric properties are observed. The presence of morphotropic phase boundary (coexistence of tetragonal and rhombohedral symmetry) is confirmed by X-ray diffraction. Enhancement of sinterability after Bi doping is observed through a systematic sintering program. Frequency and temperature dependent dielectric constant are studied. Bi doping in PZT is found to enhance room temperature dielectric constant. However, at high temperature the dielectric constant of pure PZT is more than that of dopedmore » PZT.« less

Properties of dielectric dead layers for SrTiO3 thin films on Pt electrodes

NASA Astrophysics Data System (ADS)

Finstrom, Nicholas H.; Cagnon, Joel; Stemmer, Susanne

2007-02-01

Dielectric measurements as a function of temperature were used to characterize the properties of the dielectric dead layers in parallel-plate capacitors with differently textured SrTiO3 thin films and Pt electrodes. The apparent thickness dependence of the permittivity was described with low-permittivity passive (dead) layers at the interfaces connected in series with the bulk of the SrTiO3 film. Interfacial capacitance densities changed with the film microstructure and were weakly temperature dependent. Estimates of the dielectric dead layer thickness and permittivity were limited by the film surface roughness (˜5nm ). The consequences for the possible origins of dielectric dead layers that have been proposed in the literature are discussed.

Dielectric properties of nematic liquid crystal doped with Fe3O4 nanoparticles

NASA Astrophysics Data System (ADS)

Maleki, A.; Ara, M. H. Majles; Saboohi, F.

2017-04-01

The influence of Fe3O4 nanoparticles (NPs) on dielectric properties of planar and homeotropic oriented nematic liquid crystals (NLCs) were studied during the temperature interval of 298-322 °K. It was found that the dielectric permittivity was considerably increased by adding NPs mass percentages. The structural characterization of the synthesized NPs with the scale 14-18 nm has been analyzed by the X-ray diffraction and field-emission scanning electron microscopy results. The obtained dielectric anisotropy (?) and mean dielectric (?) have shown an immense increment in the value of 1% and 10% wt. NPs doped NLCs, respectively. These results were assigned to the strong dipole-dipole interaction between the superparamagnetic particles and the surrounding liquid crystal molecules.

Dielectric studies on PEG-LTMS based polymer composites

NASA Astrophysics Data System (ADS)

Patil, Ravikumar V.; Praveen, D.; Damle, R.

2018-02-01

PEG LTMS based polymer composites were prepared and studied for dielectric constant variation with frequency and temperature as a potential candidate with better dielectric properties. Solution cast technique is used for the preparation of polymer composite with five different compositions. Samples show variation in dielectric constant with frequency and temperature. Dielectric constant is large at low frequencies and higher temperatures. Samples with larger space charges have shown larger dielectric constant. The highest dielectric constant observed was about 29244 for PEG25LTMS sample at 100Hz and 312 K.

Dielectric and electrical studies of Pr{sup 3+} doped nano CaSiO{sub 3} perovskite ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulkarni, Sandhya, E-mail: pappu.sandhyakulkarni@gmail.com; Nagabhushana, B.M.; Parvatikar, Narsimha

2014-02-01

Highlights: • CaSiO{sub 3}:Pr{sup 3+} was prepared by facile low temperature solution combustion method. • The crystalline phase of the product is obtained by adopting sintering method. • Samples prepared at 500 °C and calcined at 900 °C for 3 h showed β-phase. • The Pr{sup 3+} doped CaSiO{sub 3} shows “unusual results”. • The electrical microstructure has been accepted to be of internal barrier layer capacitor. - Abstract: CaSiO{sub 3} nano-ceramic powder doped with Pr{sup 3+} has been prepared by solution combustion method. The powder Ca{sub 0.95}Pr{sub 0.05}SiO{sub 3} is investigated for its dielectric and electrical properties at roommore » temperature to study the effect of doping. The sample is characterized by X-ray diffraction and infrared spectroscopy. The size of either of volume elements of CaSiO{sub 3}:Pr{sup 3+} estimated from transmission electron microscopy is about 180–200 nm. The sample shows colossal dielectric response at room temperature. This colossal dielectric behaviour follows Debye-type relaxation and can be explained by Maxwell–Wagner (MW) polarization. However, analysis of impedance and electric modulus data using Cole–Cole plot shows that it deviates from ideal Debye behaviour resulting from the distribution of relaxation times. The distribution in the relaxation times may be attributed to existence of electrically heterogeneous grains, insulating grain boundary, and electrode contact regions. Doping, thus, results in substantial modifications in the dielectric and electrical properties of the nano-ceramic CaSiO{sub 3}.« less

Electrical conductivity and dielectric relaxation of 2-(antipyrin-4-ylhydrazono)-2-(4-nitrophenyl)acetonitrile

NASA Astrophysics Data System (ADS)

El-Menyawy, E. M.; Zedan, I. T.; Nawar, H. H.

2014-03-01

The electrical and dielectric properties of the synthesized 2-(antipyrin-4-ylhydrazono)-2-(4-nitrophenyl)acetonitrile (AHNA) have been studied. The direct and alternating current (DC and AC) conductivities and complex dielectric constant were investigated in temperature range 303-403 K. The AC conductivity and dielectric properties of AHNA were investigated over frequency range 100 Hz-5 MHz. From DC and AC measurements, electrical conduction is found to be a thermally activated process. The frequency-dependent AC conductivity obeys Jonscher's universal power law in which the frequency exponent decreases with increasing temperature. The correlated barrier hopping (CBH) is the predominant model for describing the charge carrier transport in which the electrical parameters are evaluated. The activation energy is found to decrease with increasing frequency. The behaviors of dielectric and dielectric loss are discussed in terms of a polarization mechanism. The dielectric loss shows frequency power law from which the maximum barrier height is determined as 0.19 eV in terms of the Guintini model.

Dielectric spectroscopy in agrophysics

NASA Astrophysics Data System (ADS)

Skierucha, W.; Wilczek, A.; Szypłowska, A.

2012-04-01

The paper presents scientific foundation and some examples of agrophysical applications of dielectric spectroscopy techniques. The aim of agrophysics is to apply physical methods and techniques for studies of materials and processes which occur in agriculture. Dielectric spectroscopy, which describes the dielectric properties of a sample as a function of frequency, may be successfully used for examinations of properties of various materials. Possible test materials may include agrophysical objects such as soil, fruit, vegetables, intermediate and final products of the food industry, grain, oils, etc. Dielectric spectroscopy techniques enable non-destructive and non-invasive measurements of the agricultural materials, therefore providing tools for rapid evaluation of their water content and quality. There is a limited number of research in the field of dielectric spectroscopy of agricultural objects, which is caused by the relatively high cost of the respective measurement equipment. With the fast development of modern technology, especially in high frequency applications, dielectric spectroscopy has great potential of expansion in agrophysics, both in cognitive and utilitarian aspects.

Enhanced dielectric performance of three phase percolative composites based on thermoplastic-ceramic composites and surface modified carbon nanotube

NASA Astrophysics Data System (ADS)

Yang, Yang; Sun, Haoliang; Zhu, Benpeng; Wang, Ziyu; Wei, Jianhong; Xiong, Rui; Shi, Jing; Liu, Zhengyou; Lei, Qingquan

2015-01-01

Three-phase composites were prepared by embedding CaCu3Ti4O12(CCTO) nanoparticles and Multiwalled Carbon Nanotube (MWNT) into polyimide (PI) matrix via in-situ polymerization. The dependences of electric and dielectric properties of the resultant composites on volume fractions of filler and frequency were investigated. The dielectric permittivity of PI/CCTO-surface modified MWNT (MWNT-S) composite reached as high as 252 at 100 Hz at 0.1 vol. % filler (MWNT-S), which is about 63 times higher than that of pure PI. Also the dielectric loss is only 0.02 at 100 Hz. The results are in good agreement with the percolation theory. It is shown that embedding high aspect ratio MWNT-S in PI/CCTO composites is an effective means to enhance the dielectric permittivity and reduce the percolation threshold. The dielectric properties of the composites will meet the practical requirements for the application in high dielectric constant capacitors and high energy density materials.

Dielectric Properties and Oxidation Roasting of Molybdenite Concentrate by Using Microwave Energy at 2.45 GHz Frequency

NASA Astrophysics Data System (ADS)

Yonglin, Jiang; Bingguo, Liu; Peng, Liu; Jinhui, Peng; Libo, Zhang

2017-12-01

Conversion of electromagnetic energy into heat depends largely on the dielectric properties of the material being treated. Therefore, determining the dielectric properties of molybdenite concentrate and its microwave power penetration depth in relation to a temperature increment at the commercial frequency of 2.45 GHz is necessary to design industrial microwave processing units. In this study, the dielectric constants increased as the temperature increased in the entire experimental range. The loss factor presented an opposite trend, except for 298 K to 373 K (25 °C to 100 °C) in which a cavity perturbation resonator was used. The plots of nonlinear surface fitting indicate that the increase in dielectric loss causes a considerable decrease in penetration depth, but the dielectric constants exert a small positive effect. The thermogravimetric analysis (TGA-DSC) of the molybdenite concentrate was carried out to track its thermal decomposition process, aim to a dielectric analysis during the microwave heating. MoO3 was prepared from molybdenite concentrate through oxidation roasting in a microwave heating system and a resistance furnace, respectively. The phase transitions and morphology evolutions during oxidation roasting were characterized through X-ray diffraction and scanning electron microscopy. Results show that microwave thermal technique can produce high-purity molybdenum trioxide.

Dielectric properties of carbon nanotubes/epoxy composites.

PubMed

Peng, Jin-Ping; Zhang, Hui; Tang, Long-Cheng; Jia, Yu; Zhang, Zhong

2013-02-01

Material with high dielectric properties possesses the effect of energy storage and electric field homogenization, which plays an important role in the electrical and electronics domain, especially in the capacitor, electrical machinery and cable realm. In this paper, epoxy-based nanocomposites with high dielectric constant were fabricated by adding pristine and ozone functionalized multi-wall carbon nanotubes (MWCNTs). In the process-related aspect, the favorable technological parameter was obtained via reasonable arrangement and consideration of the dispersing methods including high-speed stirring and three-roller mill. As a result, a uniform dispersion status of MWCNTs in matrix has been guaranteed, which was observed by scanning and transmission electron microscopy. Meanwhile, the influence of different MWCNTs contents and diverse frequencies on the dielectric properties was compared. It was found that the dielectric constant of nano-composites decreased gradually with the increasing of frequency (10(3)-10(6) Hz). Moreover, as the content of MWCNTs increasing, the dielectric constant reached to a maximum of about 1,328 at 10(3) Hz when the pristine MWCNTs content was 0.5 wt.%. Accordingly, the DC conductivity results could interpret the peak value phenomenon by percolation threshold of MWCNTs. In addition, at the fixed content, the dielectric constant of epoxy-based nano-composites with ozone functionalized MWCNTs was lower than that of pristine ones.

Simultaneous observation of up/down conversion photoluminescence and colossal permittivity properties in (Er+Nb) co-doped TiO2 materials

NASA Astrophysics Data System (ADS)

Tse, Mei-Yan; Tsang, Ming-Kiu; Wong, Yuen-Ting; Chan, Yi-Lok; Hao, Jianhua

2016-07-01

We have investigated the optical and dielectric properties of rutile TiO2 doped with Nb and Er, i.e., (Er0.5Nb0.5)xTi1-xO2. The up/downconversion photoluminescence was observed in the visible and near-infrared region from the materials under 980 nm laser diode excitation. The upconversion emissions are attributed to the energy transfer between Er ions in the excited states. Moreover, the dielectric measurements indicate that the fabricated materials simultaneously present colossal permittivity properties with relatively low dielectric loss. Our work demonstrates the coexistence of both interesting luminescence and attractive dielectric characteristics in (Er+Nb) co-doped TiO2, showing the potential for multifunctional applications.

Elastomer modulus and dielectric strength scaling with sample thickness

NASA Astrophysics Data System (ADS)

Larson, Kent

2015-04-01

Material characteristics such as adhesion and dielectric strength have well recognized dependencies on material thickness. There is disagreement, however, on the scale: the long held dictum that dielectric strength is inversely proportional to the square root of sample thickness has been shown to not always hold true for all materials, nor for all possible thickness regions. In D-EAP applications some studies have postulated a "critical thickness" below which properties show significantly less thickness dependency. While a great deal of data is available for dielectric strength, other properties are not nearly as well documented as samples get thinner. In particular, elastic modulus has been found to increase and elongation to decrease as sample thickness is lowered. This trend can be observed experimentally, but has been rarely reported and certainly does not appear in typical suppliers' product data sheets. Both published and newly generated data were used to study properties such as elastic modulus and dielectric strength vs sample thickness in silicone elastomers. Several theories are examined to explain such behavior, such as the impact of defect size and of common (but not well reported) concentration gradients that occur during elastomer curing that create micron-sized layers at the upper and lower interfaces with divergent properties to the bulk material. As Dielectric Electro-Active Polymer applications strive to lower and lower material thickness, changing mechanical properties must be recognized and taken into consideration for accurate electro-mechanical predictions of performance.

Structural and dielectric studies on Ag doped nano ZnSnO3

NASA Astrophysics Data System (ADS)

Deepa, K.; Angel, S. Lilly; Rajamanickam, N.; Jayakumar, K.; Ramachandran, K.

2018-04-01

Undoped and Ag-doped nano Zinc Stannate (ZSO) ternary oxide were prepared by co-precipitation method. The crystallographic, morphological and optical properties of the synthesized nanoparticles were studied using X-ray diffraction (XRD) and UV-Visible spectroscopy (UV-Vis) and Scanning electron microscopy (SEM). The electrical properties of the synthesized samples were studied by dielectric measurements. Higher concentration Ag doped ZSO nanoparticles exhibit higher dielectric constant at low frequency.

Ab-initio molecular dynamics in electric fields via Wannier functions: Dielectric properties of liquid water.

NASA Astrophysics Data System (ADS)

Sharma, Manu; Resta, Raffaele; Car, Roberto

2004-03-01

We have implemented a modified Car-Parrinello molecular dynamics scheme in which maximally localized Wannier functions, instead of delocalized Bloch orbitals, are used to represent ``on the fly'' the electronic wavefunction of an insulating system. Within our scheme, we account for the effects of a finite homogeneous field applied to the simulation cell; we then use the ideas of the modern theory of polarization to investigate the system's response. The dielectric response (linear and nonlinear) of a given material is thus directly accessible at a reasonable computational cost. We have performed a thorough study of the behavior of a computational sample of liquid water under the effect of an electric field. We used norm-conserving pseudopotentials, the PBE exchange-correlation potential, and supercell containing water 64 molecules. Besides providing the static response of the liquid at a given temperature, our simulations yield microscopic insight into features wich are not easily measured in experiments, particularly regarding relaxation phenomena.

Dielectric Spectroscopy Analysis of Aged EVOH films with Application to Deterioration of Food Packaging Materials

NASA Astrophysics Data System (ADS)

Hoeller, Timothy

2007-06-01

Samples of EVOH films from compositions of 29 - 44 mol% ethylene content were exposed to thermal aging with and without light exposure. The results of Dielectric Spectroscopy on select samples showed Cole-Cole plots of skewed dielectric constant indicating multiple distributions of dipole relaxation times. The onset for decreases in dielectric response occurs earlier in samples exposed to elevated temperature under light exposure. Lower permittivity is exhibited in samples of higher ethylene content. Results from heat exposed samples are presented. Colorimetric analysis indicates only a slight film yellowing in one case. Raman spectroscopy on untreated films discerns changes in the C-C-O stretch associated with the alcohol. The effects of aging on microstructure may cause hindrance of molecular motion from moisture desorption. Slight material degradation occurs from film hardening presumably due to crosslinking. An electrical circuit model of the conduction processes associated with the EVOH films is presented. Dielectric analysis shows promise for monitoring material changes related to deterioration. We are also using these methods to understand Fluorescence Imaging which has been recently released for paper and plastic materials analysis. Future work may include refinement of these techniques for identification of changes in material properties correlated to packaging material barrier resistance.

Fabrication of Nd3+ and Mn2+ ions Co-doped Spinal Strontium Nanoferrites for High Frequency Device Applications

NASA Astrophysics Data System (ADS)

Ahmad, Iqbal; Shah, Syed Mujtaba; Ashiq, Muhammad Naeem; Nawaz, Faisal; Shah, Afzal; Siddiq, Muhammad; Fahim, Iqra; Khan, Samiullah

2016-10-01

Microemulsion method has been used for the synthesis of high resistive spinal nanoferrites with nominal composition Sr1- x Nd x Fe2- y Mn y O4 (0.0 ≤ x ≤ 0.1, 0.0 ≤ y ≤ 1.0) for high frequency device applications. It has been confirmed by x-ray diffraction (XRD) results that these ferrites have a cubic spinal structure with a mean crystallite size ranging from 34 mm to 47 nm. The co-substitution of Nd3+ and Mn2+ ions was performed, and its effect on electrical, dielectric and impedance properties was analyzed employing direct current (DC) resistivity measurements, dielectric measurements and electrochemical impedance spectroscopy (EIS). The DC resistivity ( ρ) value was the highest for the composition Sr0.90Nd0.1FeMnO4, but for the same composition, dielectric parameters and alternating current (AC) conductivity showed their minimum values. In the lower frequency range, the magnitudes of dielectric parameters decrease with increasing frequency and show an almost independent frequency response at higher frequencies. Dielectric polarization has been employed to explain these results. It was inferred from the results of EIS that the conduction process in the studied ferrite materials is predominantly governed by grain boundary volume.

High-throughput screening of inorganic compounds for the discovery of novel dielectric and optical materials

DOE PAGES

Petousis, Ioannis; Mrdjenovich, David; Ballouz, Eric; ...

2017-01-31

Dielectrics are an important class of materials that are ubiquitous in modern electronic applications. Even though their properties are important for the performance of devices, the number of compounds with known dielectric constant is on the order of a few hundred. Here, we use Density Functional Perturbation Theory as a way to screen for the dielectric constant and refractive index of materials in a fast and computationally efficient way. Our results constitute the largest dielectric tensors database to date, containing 1,056 compounds. Details regarding the computational methodology and technical validation are presented along with the format of our publicly availablemore » data. In addition, we integrate our dataset with the Materials Project allowing users easy access to material properties. Finally, we explain how our dataset and calculation methodology can be used in the search for novel dielectric compounds.« less

High-throughput screening of inorganic compounds for the discovery of novel dielectric and optical materials

PubMed Central

Petousis, Ioannis; Mrdjenovich, David; Ballouz, Eric; Liu, Miao; Winston, Donald; Chen, Wei; Graf, Tanja; Schladt, Thomas D.; Persson, Kristin A.; Prinz, Fritz B.

2017-01-01

Dielectrics are an important class of materials that are ubiquitous in modern electronic applications. Even though their properties are important for the performance of devices, the number of compounds with known dielectric constant is on the order of a few hundred. Here, we use Density Functional Perturbation Theory as a way to screen for the dielectric constant and refractive index of materials in a fast and computationally efficient way. Our results constitute the largest dielectric tensors database to date, containing 1,056 compounds. Details regarding the computational methodology and technical validation are presented along with the format of our publicly available data. In addition, we integrate our dataset with the Materials Project allowing users easy access to material properties. Finally, we explain how our dataset and calculation methodology can be used in the search for novel dielectric compounds. PMID:28140408

High-throughput screening of inorganic compounds for the discovery of novel dielectric and optical materials.

PubMed

Petousis, Ioannis; Mrdjenovich, David; Ballouz, Eric; Liu, Miao; Winston, Donald; Chen, Wei; Graf, Tanja; Schladt, Thomas D; Persson, Kristin A; Prinz, Fritz B

2017-01-31

Dielectrics are an important class of materials that are ubiquitous in modern electronic applications. Even though their properties are important for the performance of devices, the number of compounds with known dielectric constant is on the order of a few hundred. Here, we use Density Functional Perturbation Theory as a way to screen for the dielectric constant and refractive index of materials in a fast and computationally efficient way. Our results constitute the largest dielectric tensors database to date, containing 1,056 compounds. Details regarding the computational methodology and technical validation are presented along with the format of our publicly available data. In addition, we integrate our dataset with the Materials Project allowing users easy access to material properties. Finally, we explain how our dataset and calculation methodology can be used in the search for novel dielectric compounds.

The DC and AC insulating properties of magnetic fluids based on transformer oil

NASA Astrophysics Data System (ADS)

Tomo, L.; Marton, K.; Herchl, F.; Kopanský, P.; Potoová, I.; Koneracká, M.; Timko, M.

2006-01-01

The AC-dielectric breakdown was investigated in magnetic fluids based on transformer oil TECHNOL US 4000 for two orientations of external magnetic field (B E and B E) and in B = 0. The found results were compared with those obtained formerly for the DC-dielectric breakdown. The observations of the time development of the AC-dielectric breakdown showed the presence of partial discharges long before the complete breakdown occurrence, while for DC-dielectric breakdown a complete breakdown of the gap next to the onset of a measurable ionization was characteristic. The comparison of the AC-dielectric breakdown strengths of pure transformer oil and transformer-oil-based magnetic fluid showed better dielectric properties of magnetic fluid in external magnetic field and comparable, but not worse, in B = 0. Regarding to the better heat transfer, provided by magnetic fluids, they could be used in power transformers as insulating fluids.

Water under inner pressure: a dielectric spectroscopy study.

PubMed

Angulo-Sherman, Abril; Mercado-Uribe, Hilda

2014-02-01

Water is the most studied substance on Earth. However, it is not completely understood why its structural and dynamical properties give rise to some anomalous behaviors. Some of them emerge when experiments at low temperatures and/or high pressures are performed. Here we report dielectric measurements on cold water under macroscopically constrained conditions, i.e., water in a large container at constant volume that cannot freeze below the melting point. The inner pressure in these conditions shifts the α relaxation peak to similar frequencies as seen in ice Ih. At 267 K we observe a peculiar response possibly due to the Grotthuss mechanism. At 251 K (the triple point) ice III forms.

Optical design of nanowire absorbers for wavelength selective photodetectors

PubMed Central

Mokkapati, S.; Saxena, D.; Tan, H. H.; Jagadish, C.

2015-01-01

We propose the optical design for the absorptive element of photodetectors to achieve wavelength selective photo response based on resonant guided modes supported in semiconductor nanowires. We show that the waveguiding properties of nanowires result in very high absorption efficiency that can be exploited to reduce the volume of active semiconductor compared to planar photodetectors, without compromising the photocurrent. We present a design based on a group of nanowires with varying diameter for multi-color photodetectors with small footprint. We discuss the effect of a dielectric shell around the nanowires on the absorption efficiency and present a simple approach to optimize the nanowire diameter-dielectric shell thickness for maximizing the absorption efficiency. PMID:26469227

Room temperature magnetoelectric coupling and electrical properties of Ni doped Co - ferrite - PZT nanocomposites

NASA Astrophysics Data System (ADS)

Chakraborty, Sarit; Mandal, S. K.; Dey, P.; Saha, B.

2018-04-01

Multiferroic magnetoelectric materials are very interesting for the researcher for the potential application in device preparation. We have prepared 0.3Ni0.5Co0.5Fe2O4 - 0.7PbZr0.58Ti0.42O3 magnetoelectric nanocomposites through chemical pyrophoric reaction process followed by solid state reaction and represented magnetoelectric coupling coefficient, thermally and magnetically tunable AC electrical properties. For the structural characterization XRD pattern and SEM micrograph have been analyzed. AC electrical properties reveal that the grain boundaries resistances are played dominating role in the conduction process in the system. Dielectric studies are represents that the dielectric polarization is decreased with frequency as well as magnetic field where it increases with increasing temperature. The dielectric profiles also represents the electromechanical resonance at a frequency of ˜183 kHz. High dielectric constant and low dielectric loss at room temperature makes the material very promising for the application of magnetic field sensor devices.

Dielectric properties of crystalline organic molecular films in the limit of zero overlap

DOE Office of Scientific and Technical Information (OSTI.GOV)

D’Avino, Gabriele, E-mail: gabriele.davino@gmail.com; Vanzo, Davide; Soos, Zoltán G., E-mail: soos@princeton.edu

2016-01-21

We present the calculation of the static dielectric susceptibility tensor and dipole field sums in thin molecular films in the well-defined limit of zero intermolecular overlap. Microelectrostatic and charge redistribution approaches are applied to study the evolution of dielectric properties from one to a few molecular layers in films of different conjugated molecules with organic electronics applications. Because of the conditional convergence of dipolar interactions, dipole fields depend on the shape of the sample and different values are found in the middle layer of a thick film and in the bulk. The shape dependence is eliminated when depolarization is takenmore » into account, and the dielectric tensor of molecular films converges to the bulk limit within a few molecular layers. We quantify the magnitude of surface effects and interpret general trends among different systems in terms of molecular properties, such as shape, polarizability anisotropy, and supramolecular organization. A connection between atomistic models for molecular dielectrics and simpler theories for polarizable atomic lattices is also provided.« less

Reflectance properties of one-dimensional metal-dielectric ternary photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, G. N., E-mail: gnpandey2009@gmail.com; Kumar, Narendra; Thapa, Khem B.

2016-05-06

Metallic photonic crystal has a very important application in absorption enhancement in solar cells. It has been found that an ultra-thin metallic layer becomes transparent due to internal scattering of light through the each interface of the dielectric and metal surfaces. The metal has absorption due to their surface plasmon and the plasmon has important parameters for changing optical properties of the metal. We consider ternary metallic-dielectric photonic crystal (MDPC) for having large probabilities to change the optical properties of the MDPC and the photonic crystals may be changed by changing dimensionality, symmetry, lattice parameters, Filling fraction and effective refractivemore » index refractive index contrast. In this present communication, we try to show that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged when air dielectric constant is considered. All the theoretical analyses are made based on the transfer matrix method together with the Drude model of metal.« less

Physical and electrical properties of SrTiO3 and SrZrO3

NASA Astrophysics Data System (ADS)

Fashren Muhamad, Norhizatol; Aina Maulat Osman, Rozana; Sobri Idris, Mohd; Yasin, Mohd Najib Mohd

2017-11-01

Perovskite type oxide strontium titanate (SrTiO3) and strontium zirconate (SrZrO3) ceramic powder has been synthesized using conventional solid state reaction method. The powders were mixed and ground undergone calcinations at 1400°C for 12 h and sintered at 1550°C for 5h. X-ray Diffraction exposes physical properties SrTiO3 which exhibit cubic phase (space group: pm-3m) at room temperature meanwhile SrZrO3 has Orthorhombic phase (space group: pnma). The electrical properties such as dielectric constant (ɛr), dielectric loss (tan δ), and conductivity (σ) were studied in variation temperature and frequency. High dielectric constant of SrTiO3 and SrZrO3 were observed at 10 kHz for both samples about 240 and 21 respectively at room temperature. The dielectric loss of SrTiO3 and SrZrO3 is very low loss value approximately 0.00076 and 0.67512 indicates very good dielectric.

Compressive Strength of Cometary Surfaces Derived from Radar Observations

NASA Astrophysics Data System (ADS)

ElShafie, A.; Heggy, E.

2014-12-01

Landing on a comet nucleus and probing it, mechanically using harpoons, penetrometers and drills, and electromagnetically using low frequency radar waves is a complex task that will be tackled by the Rosetta mission for Comet 67P/Churyumov-Gerasimenko. The mechanical properties (i.e. density, porosity and compressive strength) and the electrical properties (i.e. the real and imaginary parts of the dielectric constant) of the comet nucleus, constrain both the mechanical and electromagnetic probing capabilities of Rosetta, as well as the choice of landing site, the safety of the landing, and subsurface data interpretation. During landing, the sounding radar data that will be collected by Rosetta's CONSERT experiment can be used to probe the comet's upper regolith layer by assessing its dielectric properties, which are then inverted to retrieve the surface mechanical properties. These observations can help characterize the mechanical properties of the landing site, which will optimize the operation of the anchor system. In this effort, we correlate the mechanical and electrical properties of cometary analogs to each other, and derive an empirical model that can be used to retrieve density, porosity and compressive strength from the dielectric properties of the upper regolith inverted from CONSERT observations during the landing phase. In our approach we consider snow as a viable cometary material analog due to its low density and its porous nature. Therefore, we used the compressive strength and dielectric constant measurements conducted on snow at a temperature of 250 K and a density range of 0.4-0.9 g/cm3 in order to investigate the relation between compressive strength and dielectric constant under cometary-relevant density range. Our results suggest that compressive strength increases linearly as function of the dielectric constant over the observed density range mentioned above. The minimum and maximum compressive strength of 0.5 and 4.5 MPa corresponded to a dielectric constant of 2.2 and 3.4 over the density range of 0.4-0.9 g/cm3. This preliminary correlation will be applied to the case of porous and dust contaminated snow under different temperatures to assess the surface mechanical properties for Comet 67P.

Microwave reflection measurements of the dielectric properties of concrete : final report.

DOT National Transportation Integrated Search

1983-01-01

The use of microwave reflection measurements to continuously and nondestructively monitor the hydration of concrete is described. The method relies upon the influence of the free-water content on the dielectric properties of the concrete. Use of the ...

Dielectric properties of rare earth (Sm and La) substituted lead zirconate titanate (PZT) ceramics

NASA Astrophysics Data System (ADS)

Dipti, Singh, Sangeeta; Juneja, J. K.; Raina, K. K.; Prakash, Chandra

2013-06-01

In the present paper, we are reporting the studies on dielectric properties of Lanthanum (La) and Samarium (Sm) substituted Lead Zirconate Titanate with compositional formula Pb(1.02-x)SmxZr0.55Ti0.45O3 and Pb(1.02-x)LaxZr0.55Ti0.45O3 with x = 0.00, 0.01, 0.02, 0.03. The materials were synthesized by solid state reaction route. XRD analysis shows that all the samples be in single phase with tetragonal structure. Dielectric properties were studied as a function of temperature.

Nuclear and Physical Properties of Dielectrics under Neutron Irradiation in Fast (BN-600) and Fusion (DEMO-S) Reactors

NASA Astrophysics Data System (ADS)

Blokhin, D. A.; Chernov, V. M.; Blokhin, A. I.

2017-12-01

Nuclear and physical properties (activation and transmutation of elements) of BN and Al2O3 dielectric materials subjected to neutron irradiation for up to 5 years in Russian fast (BN-600) and fusion (DEMO-S) reactors were calculated using the ACDAM-2.0 software complex for different post-irradiation cooling times (up to 10 years). Analytical relations were derived for the calculated quantities. The results may be used in the analysis of properties of irradiated dielectric materials and may help establish the rules for safe handling of these materials.

Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

PubMed Central

Scarisoreanu, N. D.; Craciun, F.; Birjega, R.; Ion, V.; Teodorescu, V. S.; Ghica, C.; Negrea, R.; Dinescu, M.

2016-01-01

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε’ ∼2500) and low dielectric loss (tan δ < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/ relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target. PMID:27157090

Aspects of spatial dispersion in the optical properties of a vacuum-dielectric interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, D.L.; Rimbey, P.R.

1976-09-15

We have examined the relationship between the polarizibility for a two-phase (vacuum-dielectric) system and the use of additional boundary conditions and the like, as regards the response of systems exhibiting spatial dispersion. As a consequence we are able to derive information about induced-charge and current densities and the continuity of the field quantities across the interface. It is shown that it is not possible to resonantly excite longitudinal bulk modes with incident light in the formalism of Rimbey-Mahan. We have derived sum rules in wave-vector space on bulk polaritions in homogeneous isotropic systems. In the case of nonhomogeneous perfect crystalsmore » in which the bulk response is described by the matrix epsilon-bar (Q, Q'), we have solved formally for the surface impedance in terms of an assumed arbitrary epsilon-bar (Q, Q'), by means of an extension of the Fuchs-Kliewer formalism. (AIP)« less

Changes in the dielectric properties of ex vivo bovine liver during microwave thermal ablation at 2.45 GHz

NASA Astrophysics Data System (ADS)

Lopresto, Vanni; Pinto, Rosanna; Lovisolo, Giorgio A.; Cavagnaro, Marta

2012-04-01

In microwave thermal ablation (MTA) therapy, the dielectric properties of the target tissue play an important role in determining the radiation properties of the microwave ablation antenna. In this work, the ex vivo dielectric properties of bovine liver were experimentally characterized as a function of the temperature during MTA at the frequency of 2.45 GHz. The obtained data were compared with measurements performed at the end of the MTA treatment, and considering the heating achieved with a temperature-controlled water bath. Finally, measured data were used to perform a numerical study evaluating the effects of changes in tissue's dielectric properties during the MTA treatment on the radiation properties of a microwave interstitial ablation antenna, as well as on the obtained thermal lesion. Results evidenced a significant decrease of both relative permittivity (about 38%) and electric conductivity (about 33%) in the tissue during treatment as the temperature increased to over 60 °C, with a dramatic drop when the temperature approached 100 °C. Moreover, the numerical study evidenced that changes in tissue's dielectric properties during the MTA treatment affect the distribution of the power absorbed by the tissue (specific absorption rate—SAR, W kg-1) surrounding the microwave interstitial ablation antenna, leading to a peak SAR up to 20% lower, as well as to a thermal lesion up to 8% longer. This work may represent a preliminary step towards the future development of a procedure for MTA treatment planning.

Dielectric properties of organic solvents from non-polarizable molecular dynamics simulation with electronic continuum model and density functional theory.

PubMed

Lee, Sanghun; Park, Sung Soo

2011-11-03

Dielectric constants of electrolytic organic solvents are calculated employing nonpolarizable Molecular Dynamics simulation with Electronic Continuum (MDEC) model and Density Functional Theory. The molecular polarizabilities are obtained by the B3LYP/6-311++G(d,p) level of theory to estimate high-frequency refractive indices while the densities and dipole moment fluctuations are computed using nonpolarizable MD simulations. The dielectric constants reproduced from these procedures are evaluated to provide a reliable approach for estimating the experimental data. An additional feature, two representative solvents which have similar molecular weights but are different dielectric properties, i.e., ethyl methyl carbonate and propylene carbonate, are compared using MD simulations and the distinctly different dielectric behaviors are observed at short times as well as at long times.

Nonintrinsic origin of the colossal dielectric constants in Ca Cu3 Ti4 O12

NASA Astrophysics Data System (ADS)

Lunkenheimer, P.; Fichtl, R.; Ebbinghaus, S. G.; Loidl, A.

2004-11-01

The dielectric properties of CaCu3Ti4O12 , a material showing colossal values of the dielectric constant, were investigated over a broad temperature and frequency range extending up to 1.3GHz . A detailed equivalent-circuit analysis of the results and two crucial experiments, employing different types of contacts and varying the sample thickness were performed. The results provide clear evidence that the apparently high values of the dielectric constant in CaCu3Ti4O12 are nonintrinsic and due to electrode polarization effects. The intrinsic properties of CaCu3Ti4O12 are characterized by charge transport via hopping of localized charge carriers and a relatively high dielectric constant of the order of 100.

Dielectric properties of soils as a function of moisture content

NASA Technical Reports Server (NTRS)

Cihlar, J.; Ulaby, F. T.

1974-01-01

Soil dielectric constant measurements are reviewed and the dependence of the dielectric constant on various soil parameters is determined. Moisture content is given special attention because of its practical significance in remote sensing and because it represents the single most influential parameter as far as soil dielectric properties are concerned. Relative complex dielectric constant curves are derived as a function of volumetric soil water content at three frequencies (1.3 GHz, 4.0 GHz, and 10.0 GHz) for each of three soil textures (sand, loam, and clay). These curves, presented in both tabular and graphical form, were chosen as representative of the reported experimental data. Calculations based on these curves showed that the power reflection coefficient and emissivity, unlike skin depth, vary only slightly as a function of frequency and soil texture.

Dielectric properties of benzylamine in 1,2,6-hexanetriol mixture using time domain reflectometry technique

NASA Astrophysics Data System (ADS)

Swami, M. B.; Hudge, P. G.; Pawar, V. P.

The dielectric properties of binary mixtures of benzylamine-1,2,6-hexantriol mixtures at different volume fractions of 1,2,6-hexanetriol have been measured using Time Domain Reflectometry (TDR) technique in the frequency range of 10 MHz to 30 GHz. Complex permittivity spectra were fitted using Havriliak-Negami equation. By using least square fit method the dielectric parameters such as static dielectric constant (ɛ0), dielectric constant at high frequency (ɛ∞), relaxation time τ (ps) and relaxation distribution parameter (β) were extracted from complex permittivity spectra at 25∘C. The intramolecular interaction of different molecules has been discussed using the Kirkwood correlation factor, Bruggeman factor. The Kirkwood correlation factor (gf) and effective Kirkwood correlation factor (geff) indicate the dipole ordering of the binary mixtures.

Effect of annealing temperature on structural, morphology and dielectric properties of La0.75Ba0.25FeO3 perovskite

NASA Astrophysics Data System (ADS)

Abdallah, F. B.; Benali, A.; Triki, M.; Dhahri, E.; Graça, M. P. F.; Valente, M. A.

2018-05-01

The effect of annealing temperature on the structure, morphology and dielectric properties of La0.75Ba0.25FeO3 compound prepared by the sol-gel method was investigated. The increase of the annealing temperature from 900 to 1100 °C, promotes an increase of the average grain size value. Two dielectric relaxations are detected using the dielectric modulus formalism, attributed to grain and grain boundary relaxations. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance and Modulus results at different measuring temperatures. The ac conductivity could be described by Jonscher's power law revealing the presence of both overlapping large polaron tunneling and non-overlapping small polaron tunneling mechanisms.

Effects of PVA organic binder on electric properties of CaCu3Ti4O12 ceramics

NASA Astrophysics Data System (ADS)

Yuan, Wen-Xiang; Li, Z. J.

2012-04-01

CaCu3Ti4O12 ceramics with incorporation of polyvinyl alcohol (PVA) are prepared from the powder synthesized by a solid state reaction. Their electric and dielectric properties are investigated in this study. It is found that adding PVA can dramatically reduce the dielectric loss of CCTO in the low frequency region, and stabilize the dependence of dielectric constant on the measuring frequency. The minimum dielectric loss of 0.045 is obtained from the sample with 8 wt% PVA. The nonlinear coefficient (α) and breakdown electric field (Eb) increase with an increase of PVA binder.

A Comprehensive Study on Dielectric Properties of Volcanic Rock/PANI Composites

NASA Astrophysics Data System (ADS)

Kiliç, M.; Karabul, Y.; Okutan, M.; İçelli, O.

2016-05-01

Basalt is a very well-known volcanic rock that is dark colored and relatively rich in iron and magnesium, almost located each country in the world. These rocks have been used in the refused rock industry, to produce building tiles, construction industrial, highway engineering. Powders and fibers of basalt rocks are widely used of radiation shielding, thermal stability, heat and sound insulation. This study examined three different basalt samples (coded CM-1, KYZ-13 and KYZ-24) collected from different regions of Van province in Turkey. Polyaniline (PANI) is one of the representative conductive polymers due to its fine environmental stability, huge electrical conductivity, as well as a comparatively low cost. Also, the electrical and thermal properties of polymer composites containing PANI have been widely studied. The dielectric properties of Basalt/Polyaniline composites in different concentrations (10, 25, 50 wt.% PANI) have been investigated by dielectric spectroscopy method at the room temperature. The dielectric parameters (dielectric constants, loss and strength) were measured in the frequency range of 102 Hz-106 Hz at room temperature. The electrical mechanism change with PANI dopant. A detailed dielectrically analysis of these composites will be presented.

Anisotropic Dielectric Properties of Carbon Fiber Reinforced Polymer Composites during Microwave Curing

NASA Astrophysics Data System (ADS)

Zhang, Linglin; Li, Yingguang; Zhou, Jing

2018-01-01

Microwave cuing technology is a promising alternative to conventional autoclave curing technology in high efficient and energy saving processing of polymer composites. Dielectric properties of composites are key parameters related to the energy conversion efficiency during the microwave curing process. However, existing methods of dielectric measurement cannot be applied to the microwave curing process. This paper presented an offline test method to solve this problem. Firstly, a kinetics model of the polymer composites under microwave curing was established based on differential scanning calorimetry to describe the whole curing process. Then several specially designed samples of different feature cure degrees were prepared and used to reflect the dielectric properties of the composite during microwave curing. It was demonstrated to be a feasible plan for both test accuracy and efficiency through extensive experimental research. Based on this method, the anisotropic complex permittivity of a carbon fiber/epoxy composite during microwave curing was accurately determined. Statistical results indicated that both the dielectric constant and dielectric loss of the composite increased at the initial curing stage, peaked at the maximum reaction rate point and decreased finally during the microwave curing process. Corresponding mechanism has also been systematically investigated in this work.

Effect of argon ion implantation on the electrical and dielectric properties of CR-39

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chawla, Mahak, E-mail: mahak.chawla@gmail.com; Shekhawat, Nidhi; Goyal, Meetika

2016-05-23

The objective of the present work is to study the effect of 130 keV Ar{sup +} ions on the electrical and dielectric properties of CR-39 samples at various doses 5×10{sup 14}, 1×10{sup 15} and 1×10{sup 16} Ar{sup +} cm{sup −2}. Current-Voltage (I-V characteristics) measurements have been used to study the electrical properties of virgin and Ar{sup +} implanted CR-39 specimens. The current has been found to be increased with increasing voltage as well as with increasing ion dose. The dielectric spectroscopy of these specimens has been done in the frequency range of 100 kHz-100 MHz. The dielectric constant has been found tomore » be decreasing whereas dielectric loss factor increases with increasing ion fluence. These kind of behavior observed in the implanted specimens indicate towards the formation of carbonaceous clusters due to the cross linking, chemical bond cleavage, formation of free radicals. The changes observed in the dielectric behavior have been further correlated with the structural changes observed through I-V characteristics.« less

All-printed, flexible, reconfigurable frequency selective surfaces

NASA Astrophysics Data System (ADS)

Haghzadeh, Mahdi; Akyurtlu, Alkim

2016-11-01

We demonstrate a new fully printed, conformal, band-pass frequency selective surface (FSS) utilizing a novel interdigitated capacitor (IDC), in which the space between the fingers can be filled with dielectric materials with different dielectric constants. Every dielectric constant corresponds to a different resonance frequency for the FSS, leading to a bandpass performance that can be tuned in a static manner based on the dielectric choice. The 2-D FSS consists of a periodic array of non-resonant and subwavelength structures (i.e., a metallic square loop and a wire grid) printed on either side of a flexible polyimide film using direct-ink writing methodologies. The miniaturized-element nature of this metamaterial-inspired FSS results in localized frequency-selective properties with very low sensitivity to the angle of incidence. Moreover, its symmetric design makes it polarization independent. A multiphase barium strontium titanate/cyclic olefin copolymer (BST/COC) composite with two different BST loadings, corresponding to two different dielectric constants, is the dielectric ink that is printed on the IDCs to vary the resonance frequency of the FSS. Different models of the FSS involving various IDC designs, with a first-order bandpass response at X-band, were simulated, printed, and measured. The center frequency of the template FSS with the air-filled IDC was tuned by 4.52% and 21.08% from 9.96 GHz by printing BST/COC dielectrics with different BST loadings on the IDCs. Moreover, the operation mode of the FSS was switched from a first order filter to a dual-band filter using printed BST/COC ink in a novel FSS design.

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

PubMed

Chi, Qingguo; Ma, Tao; Dong, Jiufeng; Cui, Yang; Zhang, Yue; Zhang, Changhai; Xu, Shichong; Wang, Xuan; Lei, Qingquan

2017-06-08

Iron Oxide (Fe 3 O 4 ) nanoparticles were deposited on the surface of low density polyethylene (LDPE) particles by solvothermal method. A magnetic field was introduced to the preparation of Fe 3 O 4 /LDPE composites, and the influences of the magnetic field on thermal conductivity and dielectric properties of composites were investigated systematically. The Fe 3 O 4 /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 Fe 3 O 4 in LDPE matrix under the action of the magnetic field, which can effectively enhance the heat flux and interfacial polarization of the Fe 3 O 4 /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 Fe 3 O 4 and LDPE. Of particular note is the dielectric properties of Fe 3 O 4 /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.

Dielectric properties of (CuO, CaO2, and BaO)y/CuTl-1223 composites

NASA Astrophysics Data System (ADS)

Mumtaz, M.; Kamran, M.; Nadeem, K.; Jabbar, Abdul; Khan, Nawazish A.; Saleem, Abida; Tajammul Hussain, S.; Kamran, M.

2013-07-01

We synthesized (CuO, CaO2, and BaO)y/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (y = 0, 5%, 10%, 15%) composites by solid-state reaction and characterized them by x-ray diffraction, scanning electron microscopy, dc-resistivity, and Fourier transform infrared spectroscopy. Frequency and temperature dependent dielectric properties, such as real and imaginary parts of the dielectric constant, dielectric loss, and ac-conductivity of these composites were studied by capacitance and conductance measurements as a function of frequency (10 kHz to 10 MHz) and temperature (78 to 300 K). X-ray diffraction analysis reveals that the characteristic behavior of the superconductor phase and the structure of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ are nearly undisturbed by doping with nanoparticles. Scanning electron microscopy images show the improvement in the intergranular linking between the superconducting grains occurring with increasing nanoparticle concentration. Microcracks are healed up with these nanoparticles, and superconducting volume fraction is also increased. Dielectric properties of these composites strongly depend on the frequency and temperature. Zero resistivity critical temperature and dielectric properties show opposite trends with the addition of nanoparticles to the Cu0.5Tl0.5Ba2Ca2Cu3O10-δ superconductor matrix.

Improvement in temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films using Ba(Mg1/3Ta2/3)O3 buffer layer

NASA Astrophysics Data System (ADS)

Wu, Zhi; Zhou, Jing; Chen, Wen; Shen, Jie; Yang, Huimin; Zhang, Shisai; Liu, Yueli

2016-12-01

In this paper, Pb(Zr0.52Ti0.48)O3 (PZT) thin films were prepared via sol-gel method. The effects of Ba(Mg1/3Ta2/3)O3 (BMT) buffer layer on the temperature dependence and dielectric tunability properties of PZT thin films were studied. As the thickness of BMT buffer layer increases, the tan δ and tunability of PZT thin films decrease while tunability still maintains above 10%. This result shows that BMT buffer layer can improve the dielectric tunability properties of PZT thin films. Furthermore, the temperature coefficient of the dielectric constant decreases from 2333.4 to 906.9 ppm/°C with the thickness of BMT buffer layer increasing in the range from 25 to 205 °C, indicating that BMT buffer layer can improve the temperature stability of PZT thin films. Therefore, BMT buffer layer plays a critical role in improving temperature dependence and dielectric tunability properties of PbZr0.52Ti0.48O3 thin films.

Effect of the addition of B{sub 2}O{sub 3} and BaO-B{sub 2}O{sub 3}-SiO{sub 2} glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu{sub 3}Ti{sub 4}O{sub 12}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shri Prakash, B.; Varma, K.B.R.

2007-06-15

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) ceramics was investigated. Both single-component (B{sub 2}O{sub 3}) and multi-component (30 wt% BaO-60 wt% B{sub 2}O{sub 3}-10 wt% SiO{sub 2} (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B{sub 2}O{sub 3} glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B{sub 2}O{sub 3} content resulted in its segregation at the grain boundaries associated with a reduction in themore » grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples. - Graphical abstract: Scanning electron micrograph of 30 wt% BaO-60 wt% B{sub 2}O{sub 3}-10 wt% SiO{sub 2} (BBS) glass-added CaCu{sub 3}Ti{sub 4}O{sub 12} ceramic on sintering.« less

Characterization of a dielectric phantom for high-field magnetic resonance imaging applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Qi, E-mail: Qi.Duan@nih.gov; Duyn, Jeff H.; Gudino, Natalia

2014-10-15

Purpose: In this work, a generic recipe for an inexpensive and nontoxic phantom was developed within a range of biologically relevant dielectric properties from 150 MHz to 4.5 GHz. Methods: The recipe includes deionized water as the solvent, NaCl to primarily control conductivity, sucrose to primarily control permittivity, agar–agar to gel the solution and reduce heat diffusivity, and benzoic acid to preserve the gel. Two hundred and seventeen samples were prepared to cover the feasible range of NaCl and sucrose concentrations. Their dielectric properties were measured using a commercial dielectric probe and were fitted to a 3D polynomial to generatemore » a recipe describing the properties as a function of NaCl concentration, sucrose concentration, and frequency. Results: Results indicated that the intuitive linear and independent relationships between NaCl and conductivity and between sucrose and permittivity are not valid. A generic polynomial recipe was developed to characterize the complex relationship between the solutes and the resulting dielectric values and has been made publicly available as a web application. In representative mixtures developed to mimic brain and muscle tissue, less than 2% difference was observed between the predicted and measured conductivity and permittivity values. Conclusions: It is expected that the recipe will be useful for generating dielectric phantoms for general magnetic resonance imaging (MRI) coil development at high magnetic field strength, including coil safety evaluation as well as pulse sequence evaluation (including B{sub 1}{sup +} mapping, B{sub 1}{sup +} shimming, and selective excitation pulse design), and other non-MRI applications which require biologically equivalent dielectric properties.« less

Accurate in vivo dielectric properties of liver from 500 MHz to 40 GHz and their correlation to ex vivo measurements.

PubMed

Farrugia, L; Wismayer, P Schembri; Mangion, L Zammit; Sammut, C V

2016-01-01

In this article, we report on the characterization of the dielectric properties of in vivo rat liver at 36.4°C from 500 MHz up to 40 GHz with less than 5% uncertainty. The measured data were fitted to a Cole-Cole model and dielectric parameters are presented together with their respective 95% confidence interval. The root mean square error is 0.42. Moreover, ex vivo measurements were conducted in situ at 1, 2, 4 and 6 min after animal death and are compared to in vivo measurements. The results show that immediate changes in [Formula: see text]and [Formula: see text] are within experimental uncertainty, and therefore changes between in vivo and published ex vivo dielectric properties can be attributed to tissue hydration.

Effect of two-stage sintering on dielectric properties of BaTi0.9Zr0.1O3 ceramics

NASA Astrophysics Data System (ADS)

Rani, Rekha; Rani, Renu; Kumar, Parveen; Juneja, J. K.; Raina, K. K.; Prakash, Chandra

2011-09-01

The effect of two-stage sintering on the dielectric properties of BaTi0.9Zr0.1O3 ceramics prepared by solid state route was investigated and is presented here. It has been found that under suitable two-stage sintering conditions, dense BaTi0.9Zr0.1O3 ceramics with improved electrical properties can be synthesized. The density was found to have a value of 5.49 g cc-1 for normally sintered samples, whereas in the case of the two-stage sintered sample it was 5.85 g cc-1. Dielectric measurements were done as a function of frequency and temperature. A small decrease in the Curie temperature was observed with modification in dielectric loss for two-stage sintered ceramic samples.

Influence of Sn doping in BaSnxTi1-xO3 ceramics on microstructural and dielectric properties

NASA Astrophysics Data System (ADS)

Ansari, Mohd. Azaj; Sreenivas, K.

2018-05-01

BaSnxTi1-x O3 solid solutions with varying Sn content (x = 0.00, 0.05, 0.15, 0.25) prepared by solid state reaction method have been studied for their structural and dielectric properties. X-ray diffraction and Raman spectroscopic analysis show composition induced modifications in the crystallographic structure, and with increasing Sn content the structure changes from tetragonal to cubic structure. The tetragonal distortion decreases with increasing Sn, and the structure becomes purely cubic for x =0.25. Changes in the structure are reflected in the temperature dependent dielectric properties. For increasing Sn content the peak dielectric constant is found to increase and the phase transition temperature (Tc) decreases to lower temperature. The purely cubic structure with x=0.25 shows a diffused phased transition.

Magnetic and Dielectric Property Studies in Fe- and NiFe-Based Polymer Nanocomposites

NASA Astrophysics Data System (ADS)

Sharma, Himani; Jain, Shubham; Raj, Pulugurtha Markondeya; Murali, K. P.; Tummala, Rao

2015-10-01

Metal-polymer composites were investigated for their microwave properties in the frequency range of 30-1000 MHz to assess their application as inductor cores and electromagnetic isolation shield structures. NiFe and Fe nanoparticles were dispersed in epoxy as nanocomposites, in different volume fractions. The permittivity, permeability, and loss tangents of the composites were measured with an impedance analyzer and correlated with the magnetic properties of the particle such as saturation magnetization and field anisotropy. Fe-epoxy showed lower magnetic permeability but improved frequency stability, compared to the NiFe-epoxy composites of the same volume loading. This is attributed to the differences in nanoparticle's structure such as effective metal core size and particle-porosity distribution in the polymer matrix. The dielectric properties of the nanocomposites were also characterized from 30 MHz to 1000 MHz. The instabilities in the dielectric constant and loss tangent were related to the interfacial polarization relaxation of the particles and the dielectric relaxation of the surface oxides.

Electrical and Dielectric Properties of a n-Si Schottky Barrier Diode with Bismuth Titanate Interlayer: Effect of Temperature

NASA Astrophysics Data System (ADS)

Yıldırım, M.; Şahin, C.; Altındal, Ş.; Durmuş, P.

2017-03-01

An Au/Bi4Ti3O12/ n-Si Schottky barrier diode (SBD) was fabricated with a 51 nm Bi4Ti3O12 interfacial layer. Admittance measurements of the fabricated SBD were carried out in the bias voltage ( V) range of -4 V and 6 V. Capacitance ( C) and conductance ( G/ω) measurements were carried out in a wide temperature range of 120-380 K so that temperature effects on electrical and dielectric properties of the SBD were investigated. Main electrical parameters were extracted from reverse bias C -2- V plots. It was found that variance of electrical and dielectric parameters of the SBD with temperature is basically different for low and high temperature regions. A fair number (˜1012 eV-1 cm-2) was obtained for surface states ( N ss); however, N ss first decreased then increased with temperature. This result was associated with increased defects with temperature and higher activation energy in the high temperature region. Dielectric parameters of the SBD were also extracted and the dielectric constant of SBD was found as ˜10 at room temperature. Application of modulus formalism to the admittance data revealed temperature-activated dielectric relaxation at 340 K. Results showed that the temperature has considerable effects on electrical and dielectric properties of Au/Bi4Ti3O12/ n-Si SBD.

Fundamental Insight on Developing Low Dielectric Constant Polyimides

NASA Technical Reports Server (NTRS)

Simpson, J. O.; SaintClair, A. K.

1997-01-01

Thermally stable, durable, insulative polyimides are in great demand for the fabrication of microelectronic devices. In this investigation dielectric and optical properties have been studied for several series of aromatic polyimides. The effect of polarizability, fluorine content, and free volume on dielectric constant was examined. In general, minimizing polarizability, maximizing free volume and fluorination all lowered dielectric constants in the polyimides studied.

Microstructural, optical and dielectric properties of La{sub 0.8}Ba{sub 0.2}FeO{sub 3} nanostructures synthesized by sol-gel combustion method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, S. Asad, E-mail: asadsyyed@gmail.com; Naseem, Swaleha; Khan, Wasi

2015-06-24

Barium doped lanthanum ferrite (LaFeO{sub 3}) nanoparticles (NPs) were prepared by gel combustion method and calcinated at 700°C. Microstructural studies were carried by XRD and SEM techniques. The results of structural characterization show the formation of all samples in single phase without any impurity. Optical properties were studied by UV- visible technique. The energy band gap was calculated and obtained 3.01 eV. Dielectric properties characterized by LCR meter and have been observed appreciable changes. The observed behavior of the dielectric properties can be attributed on the basis of Koop’s theory based on Maxwell-Wagner two layer models in studied nanoparticles.

Composition and temperature dependence of the dielectric, piezoelectric and elastic properties of pure PZT ceramics.

PubMed

Zhuang, Z Q; Haun, M J; Jang, S J; Cross, L E

1989-01-01

Pure (undoped) piezoelectric lead zirconate titanate (PZT) ceramic samples at compositions across the ferroelectric region of the phase diagram were prepared from sol-gel-derived fine powders. Excess lead oxide was included in the PZT powders to obtain dense (95-96% of theoretical density) ceramics with large grain size (>7 mum) and to control the lead stoichiometry. The dielectric, piezoelectric, and elastic properties were measured from 4.2 to 300 K. At very low temperatures, the extrinsic domain wall and thermal defect motions freeze out. The low-temperature dielectric data can be used to determine coefficients in a phenomenological theory. The extrinsic contribution to the properties can then be separated from the single-domain properties derived from the theory.

Ni doping dependent dielectric, leakage, ferroelectric and magnetic properties in Bi7Fe3-xNixTi3O21 thin films

NASA Astrophysics Data System (ADS)

Yang, B. B.; Song, D. P.; Wei, R. H.; Tang, X. W.; Hu, L.; Yang, J.; Song, W. H.; Dai, J. M.; Zhu, X. B.; Sun, Y. P.

2018-05-01

Bi7Fe3-xNixTi3O21 thin films were prepared by chemical solution deposition on Pt/Ti/SiO2/Si substrates. The Ni doping effects on the dielectric, leakage, ferroelectric and magnetic properties were investigated. Coexistence of ferroelectric and ferromagnetic properties at room-temperature was observed in the Bi7Fe2NiTi3O21 thin film with a remnant polarization 2Pr of 36.4 μC/cm2 and a remnant magnetization 2Mr of 3.9 emu/cm3. The dielectric and leakage properties were discussed in detailed. The results will provide important information to explore single-phase multiferroic materials.

High Energy Storage Density and Impedance Response of PLZT2/95/5 Antiferroelectric Ceramics.

PubMed

Li, Bi; Liu, Qiuxiang; Tang, Xingui; Zhang, Tianfu; Jiang, Yanping; Li, Wenhua; Luo, Jie

2017-02-08

(Pb 0.97 La 0.02 )(Zr 0.95 Ti 0.05 )O₃ (PLZT2/95/5) ceramics were successfully prepared via a solid-state reaction route. The dielectric properties were investigated in the temperature region of 26-650 °C. The dielectric diffuse anomaly in the dielectric relaxation was found in the high temperature region of 600-650 °C with increasing the measuring frequency, which was related to the dynamic thermal process of ionized oxygen vacancies generated in the high temperature. Two phase transition points were detected during heating, which were found to coexist from 150 to 200 °C. Electric field induced ferroelectric to antiferroelectric phase transition behavior of the (Pb 0.97 La 0.02 )(Zr 0.95 Ti 0.05 )O₃ ceramics was investigated in this work with an emphasis on energy storage properties. A recoverable energy-storage density of 0.83 J/cm³ and efficiency of 70% was obtained in (Pb 0.97 La 0.02 )(Zr 0.95 Ti 0.05 )O₃ ceramics at 55 kV/cm. Based on these results, (Pb 0.97 La 0.02 )(Zr 0.95 Ti 0.05 )O₃ ceramics with a large recoverable energy-storage density could be a potential candidate for the applications in high energy-storage density ceramic capacitors.

Dielectric property of NiTiO{sub 3} doped substituted ortho-chloropolyaniline composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakshmi, Mohana; Faisal, Muhammad; Roy, Aashish S.

2013-11-15

Ortho-chloropolyaniline (OCP)-NiTiO{sub 3} composites have been synthesized via in-situ polymerization of ortho-chloroaniline with various weight percentages of NiTiO{sub 3.} Fourier Transform Infrared spectroscopic studies of Ortho-chloropolyaniline and its composites indicated the formation of composites as a result of Vander Waal's interaction between OCP and NiTiO{sub 3} particles. Surface morphology of OCP and OCP-NiTiO{sub 3} composites were studied using Scanning Electron Microscope (SEM). The SEM micrographs indicated a modified morphology after the composite formation. Dielectric properties and electric modulus of OCP and OCP-NiTiO{sub 3} composites have been investigated in the frequency range of 50 Hz – 5 MHz. It has beenmore » noticed that electrical resistance decreases with increase in weight percentage of NiTiO{sub 3} particles in polymer matrix as well as with applied frequency. The display of semicircular arcs in Cole-Cole plots indicates the formation of series resistor and capacitor in network causing a decrease in the relaxation time and as a result conductivity enhances in these composites. The facile and cost effective synthesis process and excellent dielectric and conductivity response of these materials makes them promising materials for practical applications.« less

Dielectric property of NiTiO{sub 3} doped substituted ortho-chloropolyaniline composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakshmi, Mohana; Faisal, Muhammad; Roy, Aashish S.

Ortho-chloropolyaniline (OCP)-NiTiO{sub 3} composites have been synthesized via in-situ polymerization of ortho-chloroaniline with various weight percentages of NiTiO{sub 3.} Fourier Transform Infrared spectroscopic studies of Ortho-chloropolyaniline and its composites indicated the formation of composites as a result of Vander Waal's interaction between OCP and NiTiO{sub 3} particles. Surface morphology of OCP and OCP-NiTiO{sub 3} composites were studied using Scanning Electron Microscope (SEM). The SEM micrographs indicated a modified morphology after the composite formation. Dielectric properties and electric modulus of OCP and OCP-NiTiO{sub 3} composites have been investigated in the frequency range of 50 Hz – 5 MHz. It has beenmore » noticed that electrical resistance decreases with increase in weight percentage of NiTiO{sub 3} particles in polymer matrix as well as with applied frequency. The display of semicircular arcs in Cole-Cole plots indicates the formation of series resistor and capacitor in network causing a decrease in the relaxation time and as a result conductivity enhances in these composites. The facile and cost effective synthesis process and excellent dielectric and conductivity response of these materials makes them promising materials for practical applications.« less

Microstructure and dielectric properties of pyrochlore Bi2Ti2O7 thin films

NASA Astrophysics Data System (ADS)

Cagnon, Joël; Boesch, Damien S.; Finstrom, Nicholas H.; Nergiz, Saide Z.; Keane, Sean P.; Stemmer, Susanne

2007-08-01

Bi2Ti2O7 thin films were grown by radio-frequency magnetron sputtering on bare and Pt-coated sapphire substrates at low substrate temperatures (˜200 °C). Postdeposition anneals were carried out at different temperatures to crystallize the films. Nearly phase-pure Bi2Ti2O7 thin films with the cubic pyrochlore structure were obtained at annealing temperatures up to 800 °C. Impurity phases, in particular Bi4Ti3O12, formed at higher temperatures. At 1 MHz, the dielectric constants were about 140-150 with a very small tunability and the dielectric loss was about 4×10-3. The dielectric loss increased with frequency. The dielectric properties of Bi2Ti2O7 films are compared to those of pyrochlore bismuth zinc niobate films.

Study made of dielectric properties of promising materials for cryogenic capacitors

NASA Technical Reports Server (NTRS)

Mathes, K. N.; Minnich, S. H.

1967-01-01

Experimental investigations were conducted to determine dielectric properties of promising materials for cryogenic capacitors to be used in energy storage and pulse applications. The three classes of materials investigated were inorganic bonded ferroelectric materials, anodic coatings on metal foils, and polar low temperature liquids.

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr ,Ti)O3 thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Tang, X. G.; Tian, H. Y.; Wang, J.; Wong, K. H.; Chan, H. L. W.

2006-10-01

Ba(Zr0.2Ti0.8)O3 (BZT) thin films on Pt(111)/Ti /SiO2/Si(100) substrates without and with CaRuO3 (CRO) buffer layer were fabricated at 650°C in situ by pulsed laser deposition. The BZT thin films showed a dense morphology, many clusters are found on the surface images of BZT/Pt films, which are composed by nanosized grains of 25-35nm; the average grain size of BZT/CRO films is about 80nm, which lager than that of BZT/Pt thin film. The dielectric constants and dissipation factors of BZT/Pt and BZT/CRO thin films were 392 and 0.019 and 479 and 0.021 at 1MHz, respectively. The dielectric constant of BZT/Pt and BZT/CRO thin films changes significantly with applied dc bias field and has high tunabilities and figures of merit of ˜70% and 37 and 75% and 36, respectively, under an applied field of 400kV /cm. The possible microstructural background responsible for the high dielectric constant and tunability was discussed.

Dielectric Study of Alcohols Using Broadband Terahertz Time Domain Spectroscopy (THz-TDS).

NASA Astrophysics Data System (ADS)

Sarkar, Sohini; Saha, Debasis; Banerjee, Sneha; Mukherjee, Arnab; Mandal, Pankaj

2016-06-01

Broadband Terahertz-Time Domain Spectroscopy (THz-TDS) (1-10 THz) has been utilized to study the complex dielectric properties of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-octanol. Previous reports on dielectric study of alcohols were limited to 5 THz. At THz (1 THz = 33.33 wn = 4 meV) frequency range (0.1 to 15 THz), the molecular reorientation and several intermolecular vibrations (local oscillation of dipoles) may coexist and contribute to the overall liquid dynamics. We find that the Debye type relaxations barely contribute beyond 1 THz, rather three harmonic oscillators dominate the entire spectral range. To get insights on the modes responsible for the observed absorption in THz frequency range, we performed all atom molecular dynamics (MD) using OPLS force field and ab initio quantum calculations. Combined experimental and theoretical study reveal that the complex dielectric functions of alcohols have contribution from a) alkyl group oscillation within H-bonded network ( 1 THz), b) intermolecular H-bond stretching ( 5 THz) , and c) librational motions in alcohols. The present work, therefore, complements all previous studies on alcohols at lower frequencies and provides a clear picture on them in a broad spectral range from microwave to 10 THz.

Synthesized tissue-equivalent dielectric phantoms using salt and polyvinylpyrrolidone solutions.

PubMed

Ianniello, Carlotta; de Zwart, Jacco A; Duan, Qi; Deniz, Cem M; Alon, Leeor; Lee, Jae-Seung; Lattanzi, Riccardo; Brown, Ryan

2018-07-01

To explore the use of polyvinylpyrrolidone (PVP) for simulated materials with tissue-equivalent dielectric properties. PVP and salt were used to control, respectively, relative permittivity and electrical conductivity in a collection of 63 samples with a range of solute concentrations. Their dielectric properties were measured with a commercial probe and fitted to a 3D polynomial in order to establish an empirical recipe. The material's thermal properties and MR spectra were measured. The empirical polynomial recipe (available at https://www.amri.ninds.nih.gov/cgi-bin/phantomrecipe) provides the PVP and salt concentrations required for dielectric materials with permittivity and electrical conductivity values between approximately 45 and 78, and 0.1 to 2 siemens per meter, respectively, from 50 MHz to 4.5 GHz. The second- (solute concentrations) and seventh- (frequency) order polynomial recipe provided less than 2.5% relative error between the measured and target properties. PVP side peaks in the spectra were minor and unaffected by temperature changes. PVP-based phantoms are easy to prepare and nontoxic, and their semitransparency makes air bubbles easy to identify. The polymer can be used to create simulated material with a range of dielectric properties, negligible spectral side peaks, and long T 2 relaxation time, which are favorable in many MR applications. Magn Reson Med 80:413-419, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

High dielectric hyperbranched polyaniline materials.

PubMed

Yan, X Z; Goodson, T

2006-08-03

New organic materials for the purpose of high speed capacitor applications are discussed. The effect of the microcrystalline size dependence of different polyaniline polymeric systems on the dielectric constant is investigated. Two different methods are described for the preparation of the polyaniline dielectric materials. By sonication polymerization, the prepared polyaniline with a suggested hyperbranched structure showed much larger microcrystalline domains in comparison to the conventional linear polyaniline. Investigations of the dielectric constant and capacitance at a relatively high frequency (>100 kHz) suggested that the system with the larger microcrystalline domains (hyperbranched) gives rise to a larger dielectric constant. The mechanism of the increased dielectric response at higher frequencies is investigated by EPR spectroscopy, and these results suggest that delocalized polarons may provide a way to enhance the dielectric response at high frequency.

Dielectric Properties of Binary Solvent Mixtures of Dimethyl Sulfoxide with Water

PubMed Central

Yang, Li-Jun; Yang, Xiao-Qing; Huang, Ka-Ma; Jia, Guo-Zhu; Shang, Hui

2009-01-01

In this paper, the dielectric properties of water-dimethylsulfoxide (DMSO) mixtures with different mole ratios have been investigated in the range of 1 GHz to 40 GHz at 298 K by using a molecular dynamics (MD) simulation. Only one dielectric loss peak was observed in the frequency range and the relaxation in these mixtures can be described by a single relaxation time of the Davidson-Cole. It was observed that within experimental error the dielectric relaxation can be described by the Debye-like model (β ≈ 1, S.M. Puranik, et al. J. Chem. Soc. Faraday Trans. 1992, 88, 433 – 435). In general, the results are very consistent with the experimental measurements. PMID:19399247

Acoustic and relaxation behaviors of polydimethylsiloxane studied by using brillouin and dielectric spectroscopies

NASA Astrophysics Data System (ADS)

Lee, Byoung Wan; Ko, Jae-Hyeon; Park, Jaehoon; Shin, Dong-Myeong; Hwang, Yoon-Hwae

2016-04-01

The temperature dependences of the acoustic properties and the dielectric relaxation times of polydimethylsiloxane were investigated by using high-resolution Brillouin and broadband dielectric spectroscopies. The longitudinal sound velocity showed a large increase upon approaching the glass transition temperature while the acoustic absorption coefficient exhibited a maximum at ~263 K. Comparison of these results with previous ultrasonic data revealed a substantial frequency dispersion of the acoustic properties of this silicone-based elastomer. The relaxation times derived from the acoustic absorption peaks were consistent with the temperature dependence of the dielectric relaxation time of the structural a process, indicating a strong coupling between the acoustic waves and the segmental motions of the main chains.

Molecular dynamics simulations to study the solvent influence on protein structure

NASA Astrophysics Data System (ADS)

Dominguez, Hector

2016-05-01

Molecular simulations were carried out to study the influence of different water models in two protein systems. Most of the solvents used in protein simulations, e.g., SPC/E or TIP3P, fail to reproduce the bulk water static dielectric constant. Recently a new water model, TIP4P/ɛ, which reproduces the experimental dielectric constant was reported. Therefore, simulations for two different proteins, Lysozyme and Ubiquitin with SPC/E, TIP3P and TIP4P/ɛ solvents were carried out. Dielectric constants and structural properties were calculated and comparisons were conducted. The structural properties between the three models are very similar, however, the dielectric constants are different in each case.

Hidden symmetries in N-layer dielectric stacks

NASA Astrophysics Data System (ADS)

Liu, Haihao; Shoufie Ukhtary, M.; Saito, Riichiro

2017-11-01

The optical properties of a multilayer system with arbitrary N layers of dielectric media are investigated. Each layer is one of two dielectric media, with a thickness one-quarter the wavelength of light in that medium, corresponding to a central frequency f 0. Using the transfer matrix method, the transmittance T is calculated for all possible 2 N sequences for small N. Unexpectedly, it is found that instead of 2 N different values of T at f 0 (T 0), there are only (N/2+1) discrete values of T 0, for even N, and (N + 1) for odd N. We explain this high degeneracy in T 0 values by finding symmetry operations on the sequences that do not change T 0. Analytical formulae were derived for the T 0 values and their degeneracies as functions of N and an integer parameter for each sequence we call ‘charge’. Additionally, the bandwidth at f 0 and filter response of the transmission spectra are investigated, revealing asymptotic behavior at large N.

Electromechanical response of silicone dielectric elastomers

NASA Astrophysics Data System (ADS)

Cârlescu, V.; Prisăcaru, G.; Olaru, D.

2016-08-01

This paper presents an experimental technique to investigate the electromechanical properties of silicone dielectric elastomers actuated with high DC electric fields. A non-contact measurement technique is used to capture and monitor the thickness strain (contraction) of a circular film placed between two metallic disks electrodes. Two active fillers such as silica (10, 15 and 30 wt%) and barium titanate (5 and 15 wt%) were incorporated in order to increase the actuation performance. Thickness strain was measured at HV stimuli up to 4.5 kV and showed a quadratic dependence against applied electric field indicating that the induced strain is triggered by the Maxwell effect and/or electrostriction phenomenon as reported in literature. The actuation process evidences a rapid contraction upon HV activation and a slowly relaxation when the electrodes are short-circuit due to visco-elastic nature of elastomers. A maximum of 1.22 % thickness strain was obtained at low actuating field intensity (1.5 V/pm) comparable with those reported in literature for similar dielectric elastomer materials.

Anisotropic dielectric phase transition triggered by pendulum-like motion coupled with proton transfer in a layered hybrid crystalline material (4-nitroanilinium+) (18-crown-6) (H2PO4-) (H3PO4)2

NASA Astrophysics Data System (ADS)

Liu, Yang; Zhu, Chun-li; Qin, Liu-lei; Zheng, Xiao-yuan; Liu, Zun-qi

2018-07-01

The organic-inorganic hybrid phase-transition material, (4-nitroanilinium+) (18-crown-6) (H2PO4-) (H3PO4)2 (1), was successfully synthesized. The organic (4-nitroanilinium) (18-crown-6)+ supramolecular cation layer and inorganic phosphate anion layer were arranged alternately. Differential scanning calorimetry (DSC), temperature-dependent dielectric measurements, and variable-temperature single-crystal X-ray diffraction analysis confirmed the reversible isostructural phase transition of 1 with the same space group Pbca at 225 K, wherein the synergistic effect between the pendulum-like motion of organic cations and the proton transfer in the Osbnd H⋯O hydrogen bonding of inorganic anions was mainly responsible for the phase-transition behavior of 1. The most striking dielectric property was the remarkable anisotropy along various crystallographic axes. A potential-energy calculation further supported the possibility of dynamic motion of cations in the crystal.

Abnormal blueshift of the absorption edge in graphene nanodots

NASA Astrophysics Data System (ADS)

Sheng, Weidong

2018-06-01

In a conventional semiconductor, when the dielectric screening effect is suppressed, the exciton binding energy increases and the corresponding excitonic transition would exhibit a redshift in the spectrum. In this work, I study the optical properties of hexagonal graphene nanodots by using a configuration interaction approach and reveal that the edge of the absorption spectrum shows an abnormal blueshift as the environmental dielectric constant ɛr decreases. The two dominant many-body effects in the nanodot: the quasiparticle and excitonic effects are both found to scale almost linearly with ɛr-1. The former is shown to have a larger proportionality constant and thus accounts for the blueshift of the absorption edge. In contrast to the long-range Coulomb interaction, the on-site Coulomb energy is found to have a negative impact on the bright excitonic states. In the presence of a strong dielectric screening effect, a strong short-range Coulomb interaction is revealed to be responsible for the disintegration of the bright exciton.

Polymer Nanocomposite Materials with High Dielectric Permittivity and Low Dielectric Loss Properties

NASA Astrophysics Data System (ADS)

Toor, Anju

Materials with high dielectric permittivity have drawn increasing interests in recent years for their important applications in capacitors, actuators, and high energy density pulsed power. Particularly, polymer-based dielectrics are excellent candidates, owing to their properties such as high breakdown strength, low dielectric loss, flexibility and easy processing. To enhance the dielectric permittivity of polymer materials, typically, high dielectric constant filler materials are added to the polymer. Previously, ferroelectric and conductive fillers have been mainly used. However, such systems suffered from various limitations. For example, composites based on ferroelectric materials like barium titanate, exhibited high dielectric loss, and poor saturation voltages. Conductive fillers are used in the form of powder aggregates, and they may show 10-100 times enhancement in dielectric constant, however these nanoparticle aggregates cause the dielectric loss to be significant. Also, agglomerates limit the volume fraction of fillers in polymer and hence, the ability to achieve superior dielectric constants. Thus, the aggregation of nanoparticles is a significant challenge to their use to improve the dielectric permittivity. We propose the use of ligand-coated metal nanoparticle fillers to enhance the dielectric properties of the host polymer while minimizing dielectric loss by preventing nanoparticle agglomeration. The focus is on obtaining uniform dispersion of nanoparticles with no agglomeration by utilizing appropriate ligands/surface functionalizations on the gold nanoparticle surface. Use of ligand coated metal nanoparticles will enhance the dielectric constant while minimizing dielectric loss, even with the particles closely packed in the polymer matrix. Novel combinations of materials, which use 5 nm diameter metal nanoparticles embedded inside high breakdown strength polymer materials are evaluated. High breakdown strength polymer materials are chosen to allow further exploration of these materials for energy storage applications. In summary, two novel nanocomposite materials are designed and synthesized, one involving polyvinylidene fluoride (PVDF) as the host polymer for potential applications in energy storage and the other with SU-8 for microelectronic applications. Scanning elec- tron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy and ultramicrotoming techniques were used for the material characterization of the nanocomposite materials. A homogeneous dispersion of gold nanoparticles with low particle agglomeration has been achieved. Fabricated nanoparticle polymer composite films showed the absence of voids and cracks. Also, no evidence of macro-phase separation of nanoparticles from the polymer phase was observed. This is important because nanoparticle agglomeration and phase separation from the polymer usually results in poor processability of films and a high defect density. Dielectric characterization of the nanocomposite materials showed enhancement in the dielectric constant over the base polymer values and low dielectric loss values were observed.

Influence of temperature on Cole-Cole dielectric model of oil-immersed bushing

NASA Astrophysics Data System (ADS)

Wang, K.; Chen, X. J.; Xu, X. W.; Liu, G. Q.; Zou, D. X.; Liu, W. D.

2017-07-01

In this paper, 72.5 kV oil-immersed bushing was produced in laboratory. The frequency-domain dielectric response tests of oil-immersed bushings were carried out at different test temperatures. The experimental data were fitted by using the modified double relaxation Cole-Cole dielectric model. The influence of temperature variation on the dielectric response test of the oil-immersed bushing and the Cole-Cole dielectric model parameters were analysed. The results showed that with the increase of the test temperature, the spectrum of the real and imaginary of the complex permittivity are shifted to the high frequency direction; the parameters of the dielectric model are significantly affected by temperature.

Effect of Pentacene-dielectric Affinity on Pentacene Thin Film Growth Morphology in Organic Field-effect Transistors

DOE Office of Scientific and Technical Information (OSTI.GOV)

S Kim; M Jang; H Yang

2011-12-31

Organic field-effect transistors (OFETs) are fabricated by depositing a thin film of semiconductor on the functionalized surface of a SiO{sub 2} dielectric. The chemical and morphological structures of the interface between the semiconductor and the functionalized dielectric are critical for OFET performance. We have characterized the effect of the affinity between semiconductor and functionalized dielectric on the properties of the semiconductor-dielectric interface. The crystalline microstructure/nanostructure of the pentacene semiconductor layers, grown on a dielectric substrate that had been functionalized with either poly(4-vinyl pyridine) or polystyrene (to control hydrophobicity), and grown under a series of substrate temperatures and deposition rates, weremore » characterized by X-ray diffraction, photoemission spectroscopy, and atomic force microscopy. By comparing the morphological features of the semiconductor thin films with the device characteristics (field-effect mobility, threshold voltage, and hysteresis) of the OFET devices, the effect of affinity-driven properties on charge modulation, charge trapping, and charge carrier transport could be described.« less

Ni-coated CaCu3Ti4O12/low density polyethylene composite material with ultra-high dielectric permittivity

NASA Astrophysics Data System (ADS)

Gao, L.; Wang, X.; Chen, Y.; Chi, Q. G.; Lei, Q. Q.

2015-08-01

We report a novel low-density polyethylene (LDPE) composite filled with nickel-coated CaCu3Ti4O12 ceramic (denoted as CCTO@Ni), prepared by a melt mixing technique, and its prominent dielectric characteristics. The effects of magnetic field treatment on the dielectric properties of CCTO@Ni/LDPE composite films with a low filler concentration of 10 vol.% were investigated. Our results show that the dielectric permittivity, loss tangent, and conductivity of the LDPE composite films initially improved and then decreased with increasing treatment time under the applied magnetic field. Magnetic field treatment for 60 min led to an ultra-high dielectric permittivity value of 1.57 × 104, four orders of magnitude higher than that of the pure LDPE material. Our results indicate that the magnetic treatment may have induced a percolation effect and enhanced the interfacial polarization of the CCTO@Ni/LDPE composite, resulting in the observed changes in its dielectric properties.

Structural, dielectric and magnetic properties of NiFe2O4 prepared via sol-gel auto-combustion method

NASA Astrophysics Data System (ADS)

Sun, Li; Zhang, Ru; Wang, Zhenduo; Ju, Lin; Cao, Ensi; Zhang, Yongjia

2017-01-01

Nickelferrite (NiFe2O4)powders were synthesized via sol-gel auto-combustion method and the corresponding temperature dependence of microstructure, dielectric and magnetic properties have been investigated. Results of XRD and SEM indicate that the NiFe2O4 samples exhibit a typical single phase spinel structure and a uniform particle distribution. The dielectric constant and dielectric loss measurements show strong frequency dependence of all the samples. The peak observed in frequency dependence of dielectric loss measurements shifts to higher frequency with the increasing sintering temperature, indicating a Debye-like dielectric relaxation. The remanent magnetization increases with the increasing grain size while the coercivity is just the opposite. The saturation magnetization can achieve 50 emu/g when the sintering temperature is more than 1000 °C, and the lowest coercivity (159.49 Oe) was observed in the NFO sample sintered at 1300 °C for 2 h.

Low percolation transitions in carbon nanotube networks dispersed in a polymer matrix: dielectric properties, simulations and experiments.

PubMed

Simoes, Ricardo; Silva, Jaime; Vaia, Richard; Sencadas, Vítor; Costa, Pedro; Gomes, João; Lanceros-Méndez, Senentxu

2009-01-21

The low concentration behaviour and the increase of the dielectric constant in carbon nanotubes/polymer nanocomposites near the percolation threshold are still not well understood. In this work, a numerical model has been developed which focuses on the effect of the inclusion of conductive fillers in a dielectric polymer matrix on the dielectric constant and the dielectric strength. Experiments have been carried out in carbon nanotubes/poly(vinylidene fluoride) nanocomposites in order to compare to the simulation results. This work shows how the critical concentration is related to the formation of capacitor networks and that these networks give rise to high variations in the electrical properties of the composites. Based on numerical studies, the dependence of the percolation transition on the preparation of the nanocomposite is discussed. Finally, based on numerical and experimental results, both ours and from other authors, the causes of anomalous percolation behaviour of the dielectric constant are identified.

Dielectric breakdown strength of magnetic nanofluid based on insulation oil after impulse test

NASA Astrophysics Data System (ADS)

Nazari, M.; Rasoulifard, M. H.; Hosseini, H.

2016-02-01

In this study, the dielectric breakdown strength of magnetic nanofluids based on transformer mineral oil for use in power systems is reviewed. Nano oil samples are obtained from dispersion of the magnetic nanofluid within uninhibited transformer mineral oil NYTRO LIBRA as the base fluid. AC dielectric breakdown voltage measurement was carried out according to IEC 60156 standard and the lightning impulse breakdown voltage was obtained by using the sphere-sphere electrodes in an experimental setup for nano oil in volume concentration of 0.1-0.6%. Results indicate improved AC and lightning impulse breakdown voltage of nano oil compared to the base oil. AC test was performed again after applying impulse current and result showed that nano oil unlike the base oil retains its dielectric properties. Increase the dielectric strength of the nano oil is mainly due to dielectric and magnetic properties of Fe3O4 nanoparticles that act as free electrons snapper, and reduce the rate of free electrons in the ionization process.

Effect of DC bias on dielectric properties of nanocrystalline CuAlO2

NASA Astrophysics Data System (ADS)

Prakash, T.; Ramasamy, S.; Murty, B. S.

2013-03-01

Grain boundary effect on the room temperature dielectric behavior in mechanically alloyed nanocrystalline CuAlO2 has been investigated using impedance spectroscopy under the applied DC bias voltages 0 V to 4.8 V in a periodic interval of 0.2 V. Analysis of impedance data confirms the existence of double Schottky potential barrier heights ( Φ b ) between two adjacent grains (left and right side) with grain boundary and its influences in dielectric relaxation time ( τ), dielectric constant ( ɛ') and dielectric loss (tan δ) factor. Also, clear evidence on the suppression of Φ b was demonstrated in the higher applied bias voltages with the parameter τ. At equilibrium state, τ is 0.63 ms and it was reduced to 0.13 ms after the 3.2 V applied DC bias. These observed DC bias voltage effects are obeying `brick layer model' and also elucidates Φ b is playing a crucial role in controlling dielectric properties of nanomaterials.

Oxygen-vacancy-mediated dielectric property in perovskite Eu0.5Ba0.5TiO3-δ epitaxial thin films

NASA Astrophysics Data System (ADS)

Li, Weiwei; Gu, Junxing; He, Qian; Zhang, Kelvin H. L.; Wang, Chunchang; Jin, Kuijuan; Wang, Yongqiang; Acosta, Matias; Wang, Haiyan; Borisevich, Albina Y.; MacManus-Driscoll, Judith L.; Yang, Hao

2018-04-01

Dielectric relaxation in ABO3 perovskite oxides can result from many different charge carrier-related phenomena. Despite a strong understanding of dielectric relaxations, a detailed investigation of the relationship between the content of oxygen vacancies (VO) and dielectric relaxation has not been performed in perovskite oxide films. In this work, we report a systematic investigation of the influence of the VO concentration on the dielectric relaxation of Eu0.5Ba0.5TiO3-δ epitaxial thin films. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration in Eu0.5Ba0.5TiO3-δ films. We found that dipolar defects created by VO interact with the off-centered Ti ions, which results in the dielectric relaxation in Eu0.5Ba0.5TiO3-δ films. Activation energy gradually increases with the increasing content of VO. The present work significantly extends our understanding of relaxation properties in oxide films.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahesh, P., E-mail: pamu@iitg.ernet.in; Subhash, T., E-mail: pamu@iitg.ernet.in; Pamu, D., E-mail: pamu@iitg.ernet.in

We report the dielectric properties of (K{sub 0.5}Na{sub 0.5})NbO{sub 3} ceramics doped with x wt% of Dy{sub 2}O{sub 3} (x= 0.0-1.5 wt%) using the broadband dielectric spectroscopy. The X-ray diffraction studies showed the formation of perovskite structure signifying that Dy{sub 2}O{sub 3} diffuse into the KNN lattice. Samples doped with x > 0.5 wt% exhibit smaller grain size and lower relative densities. The dielectric properties of KNN ceramics doped with Dy{sub 2}O{sub 3} are enhanced by increasing the Dy{sup 3+} content; among the compositions studied, x = 0.5 wt% exhibited the highest dielectric constant and lowest loss at 1MHz overmore » the temperature range of 30°C to 400°C. All the samples exhibit maximum dielectric constant at the Curie temperature (∼ 326°C) and a small peak in the dielectric constant at around 165°C is due to a structural phase transition.« less

Numerical and theoretical analysis on the absorption properties of metasurface-based terahertz absorbers with different thicknesses.

PubMed

Wu, Kaimin; Huang, Yongjun; Wanghuang, Tenglong; Chen, Weijian; Wen, Guangjun

2015-01-10

In this paper, we numerically and theoretically discuss the novel absorption properties of a conventional metasurface-based terahertz (THz) electromagnetic (EM) absorber with different dielectric thicknesses. Two absorption modes are presented in the considered frequency band due to the increased dielectric thickness, and both modes can achieve near-unity absorptions when the dielectric layers reach additional nλ(d)/2 (n=1, 2) thicknesses, where λ(d) is the operating wavelength at the peak absorption in the dielectric slabs. The surface currents between the metasurface resonators and ground plane are not associated any longer, different from the conventional thin absorbers. Moreover, the EM wave energies are completely absorbed by the metasurface resonators and dielectric layer, and the main function of ground plane is to reflect the incident EM waves back to the resonators. The discussed novel absorption properties are analyzed and explained by classical EM theory and interference theory after numerical demonstrations. These findings can broaden the potential applications of the metasurface-based absorbers in the THz frequency range for different requirements.

Multi-susceptibile Single-Phased Ceramics with Both Considerable Magnetic and Dielectric Properties by Selectively Doping

PubMed Central

Liu, Chuyang; Zhang, Yujing; Jia, Jingguo; Sui, Qiang; Ma, Ning; Du, Piyi

2015-01-01

Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe3+, such as Ti4+, Nb5+ and Zr4+, into BaFe12O19. In terms of charge balance, Fe3+/Fe2+ pair dipoles are produced through the substitution of Fe3+ by high-valenced ions. The electron hopping between Fe3+ and Fe2+ ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices. PMID:25835175

Multi-susceptibile single-phased ceramics with both considerable magnetic and dielectric properties by selectively doping.

PubMed

Liu, Chuyang; Zhang, Yujing; Jia, Jingguo; Sui, Qiang; Ma, Ning; Du, Piyi

2015-04-02

Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe(3+), such as Ti(4+), Nb(5+) and Zr(4+), into BaFe12O19. In terms of charge balance, Fe(3+)/Fe(2+) pair dipoles are produced through the substitution of Fe(3+) by high-valenced ions. The electron hopping between Fe(3+) and Fe(2+) ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices.

Multi-susceptibile Single-Phased Ceramics with Both Considerable Magnetic and Dielectric Properties by Selectively Doping

NASA Astrophysics Data System (ADS)

Liu, Chuyang; Zhang, Yujing; Jia, Jingguo; Sui, Qiang; Ma, Ning; Du, Piyi

2015-04-01

Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe3+, such as Ti4+, Nb5+ and Zr4+, into BaFe12O19. In terms of charge balance, Fe3+/Fe2+ pair dipoles are produced through the substitution of Fe3+ by high-valenced ions. The electron hopping between Fe3+ and Fe2+ ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices.

Multifunctional graded dielectrics fabricated using dry powder printing

NASA Astrophysics Data System (ADS)

Good, Austin J.; Roper, David; Good, Brandon; Yarlagadda, Shridhar; Mirotznik, Mark S.

2017-09-01

The ability to fabricate multifunctional devices that combine good structural properties with embedded electromagnetic functionality has many practical applications, including antireflective surfaces for structural radomes, load bearing conformal antennas, integrated RF transmission lines and passive beam forming networks. We describe here a custom made 3D printer that can print high dielectric constant ceramic powders within a low-loss structural composite substrate to produce mechanically robust parts with integrated graded dielectric properties. We fabricated a number of these parts and evaluated their anisotropic dielectric properties by determining the complete permittivity tensor of the printed samples as a function of local powder weight. This data was then experimentally validated using two practical examples: a Chebyshev antireflective stack and a 2D passive beamsteering network. The results of both electromagnetic systems displayed acceptable agreement between the simulated and measured results. This agreement shows that powder printing is a potential approach for fabricating spatially graded dielectric electromagnetic systems. This paper was submitted for review on 15 February 2017. The project is funded by the Office of Naval Research, Code 331.

Influence of dielectric substrate on the responsivity of microstrip dipole-antenna-coupled infrared microbolometers.

PubMed

Codreanu, Iulian; Boreman, Glenn D

2002-04-01

We report on the influence of the dielectric substrate on the performance of microstrip dipole-antenna-coupled microbolometers. The location, the width, and the magnitude of the resonance of a printed dipole are altered when the dielectric substrate is backed by a ground plane. A thicker dielectric substrate shifts the antenna resonance toward shorter dipole lengths and leads to a stronger and slower detector response. The incorporation of an air layer into the antenna substrate further increases thermal impedance, leading to an even stronger response and shifting the antenna resonance toward longer dipole lengths.

Studies of ferroelectric and dielectric properties of pure and doped barium titanate prepared by sol-gel method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bisen, Supriya; Mishra, Ashutosh; Jarabana, Kanaka M.

2016-05-23

In this work, Barium Titanate (BaTiO{sub 3}) powders were synthesized via Sol-Gel auto combustion method using citric acid as a chelating agent. We study the behavior of ferroelectric and dielectric properties of pure and doped BaTiO{sub 3} on different concentration. To understand the phase and structure of the powder calcined at 900°C were characterized by X-ray Diffraction shows that tetragonal phase is dominant for pure and doped BTO and data fitted by Rietveld Refinement. Electric and Dielectric properties were characterized by P-E Hysteresis and Dielectric measurement. In P-E measurement ferroelectric loop tracer applied for different voltage. The temperature dependant dielectricmore » constant behavior was observed as a function of frequency recorded on hp-Hewlett Packard 4192A, LF impedance, 5Hz-13Hz analyzer.« less

Evaluation of high temperature dielectric films for high voltage power electronic applications

NASA Technical Reports Server (NTRS)

Suthar, J. L.; Laghari, J. R.

1992-01-01

Three high temperature films, polyimide, Teflon perfluoroalkoxy and poly-P-xylene, were evaluated for possible use in high voltage power electronic applications, such as in high energy density capacitors, cables and microelectronic circuits. The dielectric properties, including permittivity and dielectric loss, were obtained in the frequency range of 50 Hz to 100 kHz at temperatures up to 200 C. The dielectric strengths at 60 Hz were determined as a function of temperature to 250 C. Confocal laser microscopy was performed to diagnose for voids and microimperfections within the film structure. The results obtained indicate that all films evaluated are capable of maintaining their high voltage properties, with minimal degradation, at temperatures up to 200 C. However, above 200 C, they lose some of their electrical properties. These films may therefore become viable candidates for high voltage power electronic applications at high temperatures.

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yanhui, E-mail: huangy12@rpi.edu; Schadler, Linda S.

The high field charge injection and transport properties in reinforced silicone dielectrics were investigated by measuring the time-dependent space charge distribution and the current under dc conditions up to the breakdown field and were compared with the properties of other dielectric polymers. It is argued that the energy and spatial distribution of localized electronic states are crucial in determining these properties for polymer dielectrics. Tunneling to localized states likely dominates the charge injection process. A transient transport regime arises due to the relaxation of charge carriers into deep traps at the energy band tails and is successfully verified by amore » Monte Carlo simulation using the multiple-hopping model. The charge carrier mobility is found to be highly heterogeneous due to the non-uniform trapping. The slow moving electron packet exhibits a negative field dependent drift velocity possibly due to the spatial disorder of traps.« less

Plasma-Sprayed Fine-grained Zirconium Silicate and Its Dielectric Properties

NASA Astrophysics Data System (ADS)

Ctibor, P.; Pala, Z.; Nevrlá, B.; Neufuss, K.

2017-05-01

The article is focused on selected dielectric and electrical properties of ZrSiO4, which was plasma sprayed by a water-stabilized plasma system. A combination of two feeding distances and three spray distances was utilized for spraying and the structure and properties of samples evaluated. The coatings were tested in alternating electric field to determine capacity and loss factor with the frequency from 100 Hz to 100 kHz. Relative permittivity was calculated from the capacity. Volume resistivity and dielectric strength of ZrSiO4 were measured in a direct current regime. The aim was to test electrically this natural silicate material in the form of plasma-sprayed deposits. Microstructure was characterized by relatively large and non-globular pores. Crystallites were very small, about 10-20 nm. Dielectric losses were small, resistivity as well as strength relatively high. This silicate ceramic was recognized to be prospective for electrical engineering.