Broadband Dielectric Spectrometer Research Articles

Tuning the Dynamic Fragility of Acrylic Polymers by Small Molecules: The Interplay of Hydrogen Bonding Strength

High-Tg polymers exhibit high fragilities in general. Here, we report for the first time that small molecules with double phenolic end groups are effective to independently mediate the dynamic fragility (m) and glass transition temperature (Tg) of acrylic polymers. Broad band dielectric spectrometer (BDS), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimeter (DSC) measurements showed that the addition of small molecules with a concentration lower than 30 wt % leads to a narrower relaxation time distribution of the intermolecular cooperative rearrangement motion because of the formation of hydrogen bonding networks. These acrylic polymers exhibited a significant decrease in m while showing a linear increase in Tg by changing the loading of the small molecules. Further experimental results demonstrated that m decreases monotonically with intermolecular hydrogen bonding strength for a given host polymer matrix. The m/Tg value diminishes with increasing small molecule content,...

Two advanced research methods: Frequency-time-resolved microwave photoconductivity and broadband photodielectric spectroscopy

Two known methods of research of electric properties were applied on semiconducting materials and their methodology was significantly improved to obtain quantitative data on elementary reactions of charge carriers. The resonator method of microwave photoconductivity included the measurements of the frequency dependences of photoresponse. The modified frequency- and time-resolved microwave photoconductivity method gives the opportunity to separate contributions to a photoresponse of the free electrons which did not experience capture by acceptors and structural defects, and the electrons which are again released in a free state from traps. The use of a light source (λ = 350 ÷ 2500 nm) together with a broadband dielectric spectrometer provides an effective tool (the broadband photodielectric spectroscopy—BPDS) for research of relaxation processes in semiconductors caused by excess current carriers. Examples of investigation of the photoelectric properties of CdS, CdTe, and Cu(In,Ga)Se2 received with modified methods are presented.

Studies on formation of star-shaped nanostructures in chitosan films induced by lithium salts

Lithium ion batteries are an important area of research. The use of biodegradable polymers in batteries has gained importance recently. To have high efficiency, the lithium ions available for conductivity should be high. Understanding the effect of LiClO4 upon the assembly of polymers could be useful. For that, chitosan films with LiClO4 were chosen. We have used various techniques that include X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), small-angle neutron scattering (SANS), and broadband dielectric spectrometer (BDS) for our study. Our investigations show that LiClO4 induce the assembly of chitosan as star-like nanostructures. The assembly of the polymer chains could trap the ions and affect the conductivity. Our investigations show that LiClO4 encapsulates the chitosan and forms globule-like structures. This research could help us in our understanding of using biomolecules for lithium ion batteries.

Improvement of dielectric loss of Ba0.75Sr0.25TiO3 tunable material by La0.5Na0.5TiO3 addition

The structure and microstructure of (1 − x)Ba0.75Sr0.25TiO3–xLa0.5Na0.5TiO3 solid solution were investigated by XRD, Raman and microscopy analysis in this study. The temperature dependent dielectric properties and tunability under DC field were investigated at low frequencies with broad band dielectric spectrometer. Microwave dielectric properties were measured with a network analyzer. The compound demonstrated relaxor behavior when x ≤ 0.4 and incipient ferroelectric character when x ≥ 0.6, respectively. The dielectric permittivity (er) and tunability decreased, whereas the Q × f value increased with increasing x. The material with dielectric constant ~273, Q × f = ~1,700 GHz at 2.8 GHz and tunability ~9 % at E = 4,000 V/mm were obtained.

Dielectric spectroscopy studies of ZnO single crystal

Dielectric relaxation and charge transport induced by electron hopping in ZnO single crystal are measured by using a novocontrol broadband dielectric spectrometer. Typical Debye-like dielectric relaxation originating from electronic hopping between electronic traps and conductive band in surface Schottky barrier region is observed for ZnO single crystal-Au electrode system. However, after insulation of ZnO single crystal by heat treatment in rich oxygen atmosphere, dielectric relaxation and alternating current conductance are observed simultaneously in the dielectric spectra, implying that dielectric relaxation and charge transport can be induced simultaneously by electronic hopping at high temperature in an ordered system. The intrinsic correlation between local dielectric relaxation and long range charge transport offers us a new method to explore complicated dielectrics.

Yield strength of microcrystalline cellulose: Experimental evidence by dielectric spectroscopy

The water-induced ionic charge transport in compacted microcrystalline cellulose (MCC) has been reported to be governed by the densification behaviour. Hence, mechanical properties were expected to correlate with conductivity behaviour of MCC compacts. Both in-die and out-of-die compaction behaviour of MCC powder was investigated using a fully instrumented rotary tablet press. The dielectric measurements were carried out using a Novocontrol Concept 40 broadband dielectric spectrometer and dc conductivity (σdc) was extracted from the low frequency conductivity data at room temperature. As postulated, compaction pressure corresponding to maximum conductivity (σdc max) was observed to correlate with yield strength of MCC, determined using in-die and out-of-die Heckel analysis. Although Heckel transformation is most commonly used in pharmaceutical technology, its general use to characterise the mechanical properties of organic pharmaceutical materials has been criticized. The present study has provided experimental evidence that Heckel equation is practically useful to describe plastic deformation of organic pharmaceutical powders.

Fabrication and dielectric properties of Na0.5Bi0.5Cu3Ti4O12/poly(vinylidene fluoride) composites

Na0.5Bi0.5Cu3Ti4O12 (NBCTO)/poly(vinylidene fluoride) (PVDF) composites with various NBCTO volume fractions were prepared via solution mixing and hot pressing process. The structure, morphology, and dielectric properties of the composites were characterized with X-ray diffraction (XRD), thermal-gravimetric analysis (TGA), scanning electron microscope (SEM), and broadband dielectric spectrometer. The dielectric constant (e) and dielectric loss (tan δ) of the composites were both found to increase with increasing NBCTO volume fraction within the frequency range of 1–106 Hz at room temperature. Relatively high dielectric constant of 79.8 and low loss of 0.21 at 1 kHz were obtained for the NBCTO/PVDF composite with 50 vol% NBCTO. Additionally, theoretical models like Logarithmic mixture rule, Maxwell–Garnet, Effective medium theory, and Yamada model were also employed to predict the dielectric constant of these composites. The values obtained by the EMT model are in close agreement with the experimental values.

Broadband Dielectric Spectroscopy Analysis of Dielectric Properties of Barium Titanate Ceramics

The complex dielectric behaviors of ferroelectric barium titanate (BT) ceramics were investigated. The dielectric properties were studied as a function of temperature and frequency using broadband dielectric spectrometer. The results show that the maximum value of dielectric constant occurs at 500nm BT ceramics, which is approximately 7,500; the dielectric loss is lower than 0.03 with the temperature varying from 225 K to 450 K. Dielectric constant and dielectric loss experience three dielectric peaks corresponding to rhombohedral to orthorhombic, tetragonal and cubic transitions. With the frequency ranges from 1 MHz to 1 GHz, the dielectric relaxation is apparently present. The relaxation process obeys Cole-Cole relaxation model at high temperature and conforms to Debye relaxation model when the temperature far lower than Curie temperature. The relaxation time is the order magnitude of ~10-9s obtained by Havriliak-Negami function fitting, which is very consistent with theoretical calculation.

Thermal, structural and electrical studies of bismuth zinc borate glasses

Bismuth Zinc Borate glasses with compositions xBi2O3–30ZnO–(70 − x)B2O3 (where x = 30, 35, 40 and 45 mol %) have been prepared by melt quenching method. These glasses were characterized by X-ray diffraction (XRD), Differential Thermal Analysis (DTA), Fourier Transform Infrared Spectrometer (FTIR) and Broad Band Dielectric Spectrometer (BDS). DTA and FTIR analysis reveals that Non-Bridging Oxygens (NBOs) increase with increase of bismuth content in the glass. Electrical data have been analyzed in the framework of impedance and modulus formalisms. The activation energy for dc conductivity decreases with increase of bismuth concentration. The imaginary part of modulus spectra has been fitted to non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent (β) is found to be almost independent of temperature but slightly dependent on composition.

Molecular Mobility as a Predictor of the Water Sorption by Annealed Amorphous Trehalose

The work aims at investigating the correlation of water sorption potential with different measures of molecular mobility in an annealed amorphous model compound (trehalose). Amorphous trehalose, prepared by freeze-drying, was annealed at 100°C (17°C < T (g)) for up to 120h. Global molecular mobility was studied using a broadband dielectric spectrometer in the frequency range of 10(6)-10(-2) Hz. Enthalpic recovery was measured by differential scanning calorimetry and water sorption profiles were obtained using an automated vapor sorption balance. As a function of annealing time, there was an increase, both in average α-relaxation time and enthalpic recovery and a decrease in the amount of sorbed water. A strong linear correlation was observed between the water sorption potential and the dielectric relaxation time, indicating a common underlying mechanism of the effect of annealing time on these properties. Enthalpic recovery, which is widely used as a measure of structural relaxation, did not correlate well with the extent of water sorption. The α-relaxation time can be used as a predictor of the water sorption potential of amorphous trehalose. It will be of interest and value to develop such predictive models for other amorphous compounds of pharmaceutical interest.

Investigation on anticorrosion performance of epoxy based lignosulphonate doped polyaniline-poly(acrylamide co-acrylic acid) coating for AA2024 alloy

Lignosulfonate doped polyaniline-poly(acrylamide co-acrylic acid) (Pani-PAmAc) particles were synthesized by chemical polymerization method. Pani-LGS and Pani-PAmAc particles were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), broadband dielectric spectrometer (BDS) and thermogravimetric analysis (TGA). Pani-PAmAc particles were blended with epoxy to form coating system for corrosion protection of AA2024 aluminium alloy. Surface morphology of coatings was characterized by SEM. Electrical conductivity was measured by BDS. Corrosion studies were carried out by potentiodynamic polarization technique and salt spray test. Results show that epoxy based Pani-PAmAc coating was smooth and continuous. Potentiodynamic and salt spray test have shown excellent corrosion protection even after 50 days exposure to 3.5% NaCl environment. This was due to synergistic effect of polyaniline with poly(acrylamide co-acrylic acid) which prevent from dopant loss and maintain the conduction of electron even after long term exposure to corrosive environment.

Temperature dependence of the dielectric constant of acrylic dielectric elastomer

The dielectric constant is an essential electrical parameter to the achievable voltage-induced deformation of the dielectric elastomer. This paper primarily focuses on the temperature dependence of the dielectric constant (within the range of 173 K to 373 K) for the most widely used acrylic dielectric elastomer (VHB 4910). First the dielectric constant was investigated experimentally with the broadband dielectric spectrometer (BDS). Results showed that the dielectric constant first increased with temperature up to a peak value and then dropped to a relative small value. Then by analyzing the fitted curves, the Cole–Cole dispersion equation was found better to characterize the rising process before the peak values than the Debye dispersion equation, while the decrease process afterward can be well described by the simple Debye model. Finally, a mathematical model of dielectric constant of VHB 4910 was obtained from the fitted results which can be used to further probe the electromechanical stability of the dielectric elastomers.

Magnetic and electrical properties of Co1−x Cax Fe2O4 nanoparticles synthesized by the auto combustion method

Nano-sized particles of Co1−x Cax Fe2O4 (x=0.0, 0.01, 0.03, 0.05, 0.07 and 0.09) have been prepared by using the citrate-nitrate auto combustion method. X-Ray diffraction analysis has ensured the formation of the desired ferrites and has been used also to determine some of their structural properties. The particle size of only three samples has been checked out by using both transmission electron microscope (TEM) and particle size analyzer (PSA). Magnetic measurements have been performed by using vibrating sample magnetometer (VSM) at room temperature. The reduction of saturation magnetization of the nano-structured samples in comparison to bulk samples in literature and the effect of Ca addition on saturation magnetization and coercivity of all the samples are discussed. The AC conductivity and dielectric properties of these spinel ferrite nanoparticles have been investigated too as function of frequency at room temperature by using a broadband dielectric spectrometer. The AC conductivity of all the samples has been found to increase with increasing Ca substitution. This behavior is interpreted according to a suggested cationic distribution in agreement with literature and in consistency with the dielectric and loss factor results.

Electrospinning Fabrication of Tb(BA)3phen/PANI/PVP Luminescence-Electricity Bifunctional Composite Nanofibers

A new kind of luminescence-electricity bifunctional Tb(BA)3phen/PANI/PVP composite nanofibers was fabri- cated through doping of polyaniline (PANI) and terbium complex (Tb(BA)3phen) in polyvinyl pyrrolidone (PVP) via elec- trospinning. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), fluorescence spectrometer and broadband dielectric spectrometer were used to characterize the samples. The results indicated that the average diameter of the Tb(BA)3phen/PANI/PVP composite nanofibers was ca. (331±43) nm. Under the excitation of 276 nm ultraviolet, Tb(BA)3phen/PANI/PVP composite nanofibers emitted the predominant emission peaks at 491, 547 and 585 nm, corre- sponding to 5 D4→ 7 F6, 5 D4→ 7 F5 and 5 D4→ 7 F4 transitions of Tb 3 + , respectively. The strongest emission intensity was acquired when the mass ratios of Tb(BA)3phen, PANI and PVP was 15∶10∶100. The electric conductivity of the composite nanofi- bers was increased with the increase of PANI content, and reached 1.531×10 -6 S/cm in high frequency electric field (10 6 Hz) when the mass ratio of PANI to PVP was 50%. The luminescent intensity and electric conductivity of Tb(BA)3phen/ PANI/PVP composite nanofibers can be tuned via adding of various amounts of Tb(BA)3phen and PANI into the composite nanofibers. This preparative technique is of universal significance and can be used to fabricate other similar bifunctional lu- minescence-electricity composite nanofibers. This new type bifunctional luminescence-electricity composite nanofibers will have wide applications in many fields due to their excellent fluorescence and conductivity. Keywords electrospinning; Tb(BA)3phen/PANI/PVP; nanofiber; polyaniline

Research on Dielectric Spectrum Characteristics of Nano Fe3O4 Modified LDPE

Fe3O4 ferrite nanoparticles used for preparation of PE composite have been prepared by chemical co-precipitation method and modified by different methods. And the nanoFe3O4/LDPE composite materials with different mass percentage concentration of 0.25 to 1 percent were prepared by melt blending. The relationship of permittivity and dissipation factors dependence of frequency were investigated by Broadband Dielectric Spectrometer made by novo-control company. Through these measurements we got the conclusion that both the doping of Fe3O4 and magnetization have effect on permittivity and dissipation factors, and the effect relates to the doping methods and quality percentage content.

Influences of Corrosive Sulfur on Copper Wires and Oil-Paper Insulation in Transformers

Oil-impregnated paper is widely used in power transmission equipment as a reliable insulation. However, copper sulphide deposition on oil-paper insulation can lead to insulation failures in power transformers. This paper presents the influences of copper sulfur corrosion and copper sulphide deposition on copper wires and oil-paper insulation in power transformers. Thermal aging tests of paper-wrapped copper wires and bare copper wires in insulating oil were carried out at 130 °C and 150 °C in laboratory. The corrosive characteristics of paper-wrapped copper wires and bare copper wires were analyzed. Dielectric properties of insulation paper and insulating oil were also analyzed at different stages of the thermal aging tests using a broadband dielectric spectrometer. Experiments and analysis results show that copper sulfide deposition on surfaces of copper wires and insulation paper changes the surface structures of copper wires and insulation paper. Copper sulfur corrosion changes the dielectric properties of oil-paper insulation, and the copper sulfide deposition greatly reduces the electrical breakdown strength of oil-paper insulation. Metal passivator is capable of preventing copper wires from sulfur corrosion. The experimental results are helpful for investigations for fault diagnosis of internal insulation in power transformers.

Core-shell structured poly(methyl methacrylate)/BaTiO3 nanocomposites prepared by in situ atom transfer radical polymerization: a route to high dielectric constant materials with the inherent low loss of the base polymer

Core-shell structured BaTiO3/poly(methyl methacrylate) (PMMA) nanocomposites were successfully prepared by in situ atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) from the surface of BaTiO3 nanoparticles. A broadband dielectric spectrometer was used to investigate the temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 0.1 Hz to 1 MHz. It was found that the nanocomposites not only showed a significantly increased dielectric constant when compared with pure PMMA, but also showed the inherent low loss of the base polymer in a wide range of frequencies. Only in the very low frequency/high temperature range, can a higher dielectric loss can be observed in the nanocomposites. It was also found that the effective dielectric constant of the core-shell structured hybrid nanoparticles can be tailored by varying the polymer shell thickness. The dielectric response of beta relaxation of PMMA was also studied and the results showed that the nanoparticles had no influence upon the relaxation activation energy. Fourier-transform infrared spectroscopy (FTIR) and 1H NMR spectra confirmed the chemical structure of the PMMA shell on the surface of the BaTiO3 nanoparticles. Transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) results revealed that the PMMA shell thickness could be well controlled by tuning the feed ratio of MMA to BaTiO3.

Extrinsic effects on dielectric response of ultrafine grain BaTiO3 ceramics

The complex dielectric response of ultrafine grain barium titanate ceramics is investigated using broadband dielectric spectrometer. Extrinsic effects like conduction, space charge associating with grain boundaries are discussed. One dielectric relaxation ascribes to the interaction of defects with grain boundaries, for which the activation energy fitted by Arrhenius equation is equivalent to 0.26 eV and the value shifts to 0.41 eV after annealing treatment. Another relaxation phenomenon locating at elevated temperature can be attributed to interfacial polarization due to space charge accumulation effect. The study of complex impedance spectra suggests that grain boundary effects support extrinsic mechanism.

Non-phenomenological description of complex dielectric permittivity of metal-containing porous glasses

The main aim of this paper is the theoretical and experimental study of the dielectric characteristics of composite materials based on porous non-organic glasses containing metal nanoparticles. Dielectric properties of the materials were investigated using a Broad Band Dielectric Spectrometer (NOVOCONTROL BDS 80) over wide frequency (0.1–10 5 Hz) and temperature (−120 to 300 °C) ranges. For a description of dielectric response of such composite materials, a non-phenomenological model has been proposed based on the hopping of electrons between glass traps around the metal nanoparticles. The model provided an insight into the dependence of the dielectric properties of the nanocomposites, depending on nature and concentration of nanoparticles, their size distribution, temperature dependence and type of matrix. The results of the model demonstrate the physically justified features.

Grainboundary electronic structure of ZnO-Bi2O3 based varistor ceramics

Dielectric frequency spectra of ZnO-Bi2O3 based varistor ceramics were measured in the frequency range of 10-2Hz—106Hz from -100℃ to 20℃ by Novocontrol broadband dielectric spectrometer. The intrinsic defect structure of ZnO was calculated according to the theory which assumes that characteristics dielectric loss peaks of ZnO varistor ceramics origin from electronic relaxation process of intrinsic defects in depletion layer. At the same time the micro-electric parameters of grainboundary and the single grainboundary breakdown voltage Vb were obtained. The accordance of theory with experiment in Vb value indicates that the method to calculate grainboundary electronic structure by dielectric spectroscopy proposed in this paper is resonable.