Low-frequency Dielectric Spectroscopy Research Articles

Low-frequency dielectric spectroscopy of BaTiO3:Ce3+ ceramics

Dielectric spectroscopy of BaTiO3 (BT) doped with Ce3+ (BT:Ce3+) ceramics was performed at extended temperatures and in the low-frequency ranges. BT:Ce3+ displays decreasing values of all phase transition temperatures with increasing Ce3+ content. Permittivity versus temperature plots showed decreasing values with increasing frequency with low dispersion and shifting values of the Curie temperatures (Tc) towards high frequencies. Comparable values of losses for BT and BT:Ce3+ ceramics suggest good charge compensation. At low frequencies and higher temperatures, thermally activated mechanisms of conduction increase the loss values. With increasing frequency, the BT:Ce3+ system displays increased and shifted loss peaks up to Tc and decreasing values above Tc. The characteristic exponent of the modified Curie–Weiss law is higher than one. These figures suggest a relaxor-like behaviour of BT:Ce3+ ceramics for low Ce3+ content. Phase diagrams of BT:Ce3+ ceramics show a strong decrease of Tc for low Ce3+ content.

Low-frequency and temperature-dependent dielectric spectroscopy investigations on polypyrrole nanoparticles

Polypyrrole (PPy) nanoparticles have been synthesized by chemical oxidation method in the presence of anionic surfactant (sodium dodecyl sulphate). The prepared nanoparticles have a diameter of ~28 nm. The low-frequency and temperature-dependent dielectric properties of these nanoparticles have been studied in the temperature range of 77–350 K. Due to absence of the saturated loss peaks, modulus approach has been used for the further insight on the dielectric properties of prepared nanoparticles. The behaviour of the dielectric modulus suggests the Debye-type behaviour of the prepared nanoparticles, where the measured ac conductivity follows the classical hopping conduction mechanism.

Low frequency dielectric spectroscopy of bitumen binders as an indicator of adhesion potential to quartz aggregates using Portland cement

The purpose of this investigation was to interpret the bitumen-aggregate adhesion based on the dielectric spectroscopic response of individual material components utilizing their dielectric constants, refractive indices and average tangent of the dielectric loss angle (average loss tangent). Dielectric spectroscopy of bitumen binders at room temperature was performed in the frequency range of 0.01–1000 Hz. Dielectric spectroscopy is an experimental method for characterizing the dielectric permittivity of a material as a function of frequency. Adhesion data has been determined using the Rolling bottle method. The results show that the magnitude of the average tangent of the dielectric loss angle (average loss tangent) depends on bitumen type. The average loss tangent in the frequency range 0.01–1 Hz is introduced as a potential indicator for predicting polarizability and, thereby, adhesion potential of bitumen binders to quartz aggregates when using Portland cement. In order to obtain acceptable adhesion of 70/100 penetration grade bitumen binders and quartz aggregates when using Portland cement, it is suggested that the binder have an average tan δ > 0.035 in the frequency range 0.01–1 Hz.

Transformation from γ to α modification in glycine crystal

In glycine crystal the transformation from γ to α modification has been investigated using differential scanning calorimetry (DSC) and low-frequency dielectric spectroscopy methods on powder and monocrystalline samples. In monocrystalline samples the transition begins at 457.5 K. The first step is connected with cracking of the sample and growing of the ac conductivity which reaches maximum at 458.5 K. Next, ac conductivity achieves a huge maximum at the transition point 462.8 K. Additional small anomaly in the complex dielectric constant was revealed at 335 K. In powder samples this transformation measured by the DSC method goes uniformly. For these samples the ac conductivity begins to grow rapidly from 455 K and grows 2.5 times in the range of 383–387 K. In powder samples the ac conductivity at the transition point is seven times greater than in the monocrystalline samples. Conductivity anomalies are accompanied by changes in the real part of the dielectric constant.

Dielectric spectroscopy of [P(NID2OD-T2)]n thin films: Effects of UV radiation on charge transport

Poly[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyll-alt-5,5′-(2,2′-bithiophene)]-[P(ND12OD-T2)]n is a n-doped polymer that is stable in air. Low frequency (40Hz–30kHz) dielectric spectroscopy shows that the polymer impedance strength is reduced under ultra-violet (UV) radiation as a result of charge increase in the bulk polymer. Photo-excitation and the creation of electron-hole pairs and subsequent hole recombination with electron trapping species adsorbed by the polymer are suggested as possible doping mechanisms. The relaxation times were also faster in the presence of UV indicating multiple pathways for oscillating dipoles to relax. These results imply increased polymer conductance with corresponding enhancement of charge mobility due to reduced scattering in the presence of UV radiation. A thin film field effect transistor was fabricated using this polymer as the active material and characterized in the presence of UV radiation. As expected, the device exhibited n-type behavior with a charge mobility of 3.0×10−3cm2/V-s. Exposure to UV radiation increased the channel current, shifted the threshold voltage to more negative values and doubled the value of the mobility. These results are consistent with dielectric measurements and suggest an easy method of increasing device currents and charge mobility in this polymer via UV irradiation.

The Effect of An Inorganic Filler on the Properties of High-Density Polyethylene

Low-frequency dielectric spectroscopy was used to study polymer composites with a piezoelectric filler. In a wide frequency range (ν = 25 × 106 Hz) and temperature range (273-423 K), the dielectric characteristics (∊ and tg δ) and electrical conductivity (σ) of polymer composites with a piezoelectric filler were investigated. The dependences of ∊, tg δ, and σ on the concentration (up to 10 vol%) of filler, the frequency of the electric field, and temperature were studied. It was established that the introduction into high-density polyethylene of PKR-3M segnetopiezoelectric filler of the lead zirconate titanate family has a considerable effect on the given characteristics and changes the form of the dependences tg δ(ν), tg δ(T), ∊(T), and σ(T). The variance dependence σ(ν) satisfies the condition σ ∼ ns and exhibits two linear sections with parameters S ≈ 0.8 and S > 1.2 respectively.

On a different approach toward low-frequency dielectric spectroscopy measurements of conductive liquids

Driven by recent interest in the low-frequency Debye-like relaxations in hydrogen bonding liquids, here we present an alternative method for measuring such relaxations without the detrimental effects of ionic conductivity or electrode polarization. Glycerol was chosen as a molecule of interest, and a fit for the α-transition using the Vogel-Fulcher-Tammann equation was found to be τ = 2.31 × 10(-14) exp(2110 K∕[T-135 K]). This method is easily adaptable by most laboratories with existing dielectric spectrometers, and could prove useful in the accurate measurement of relaxations in conductive media at low frequencies. A brief summary of comparable techniques is also presented.

Combined low-frequency and microwave dielectric spectroscopy

Combined use of measuring setups for investigation of dielectric materials in two regions of low (10−1 to 106 Hz) and microwave (1011 to 1012 Hz) frequencies is described. Good agreement of the experimental results is obtained for the test sample.

Analysis of the dielectric spectra of composite sealing coatings in a wide frequency range

Polymer coatings on the basis of the biphenol-Novolac potting epoxy compound with a 65% content of spherical particles of fused quartz as a filler were studied by the method of dielectric spectroscopy in a wide frequency range. Dielectric measurements were performed in frequency and temperature ranges of (10−2 to 5 × 109) Hz and 20 to 200°C, respectively, on film samples of composite coatings formed on different substrates. It was shown that the application of dielectric spectroscopy allows one to study the effect of the degree of the adhesion interaction with the substrate on the processes of structuring in the epoxy polymer matrix and to investigate the degradation processes in the coatings under the effect of high temperature and relative humidity. It was also shown that the values of the glass transition temperature (Tg) of the composite determined by applying the method of low-frequency dielectric spectroscopy agree well with the Tg values obtained by applying the method of dynamic mechanical analysis (DMA).

Electrical properties of nematic liquid crystals doped with anatase TiO2 nanoparticles

This study focuses on the electrical characteristics of nematic liquid crystals doped with anatase titania nanoparticles (NPs). Low-frequency dielectric spectroscopy between 10−2 and 103 Hz is used to investigate the space-charge polarization. The results indicate that the doped samples have lower ionic concentration, diffusion constant and activation energy due to the effect of the dopant on ion transport. Temperature-dependent data provide an insight into the feasibility of using these NPs as a dopant to promote the device performance in a real environment. Verified by the voltage holding ratio, it is clear that doping anatase NPs into liquid crystals is a potentially cost-effective and easy way to improve the device performance.

Suitable Characterization Methods and Insulating Materials for Devices Operating above 200 °C

Two characterization techniques, the steady-state Conduction Current (CC) and the low frequency Dielectric Spectroscopy (DS) are reviewed and compared to each other in order to choose the most suitable method for evaluating the static electrical conductivity (σDC) of an insulating material. In the case of polymeric materials operating above 200°C, the DS appears as being better suited. These techniques are applied for insulating materials identified as good candidates for high temperature (HT) applications and new results are presented. HT polyimide, parylene films and silicon nitride substrates are studied. These examples highlight the σDC magnitudes for temperatures up to 400 °C, as well as other relevant parameters to be taken into account for practical applications.

Design of a measurement cell for low-frequency dielectric spectroscopy of biological cell suspensions

Dielectric spectroscopy of biological cell suspensions has a serious problem at low frequencies, where electrode polarization (EP) effects mostly mask their dielectric spectra. This paper describes a new type of measurement cell capable of extending the available low-frequency region by shifting the EP effects toward low frequencies. Its effectiveness was evaluated by computer simulation and experimental measurement on suspensions of erythrocytes and ghosts (hypotonically lysed erythrocytes). The results showed that the available low-frequency region was extended about ten times as compared with a corresponding conventional measurement cell, and that the low-frequency dispersion (so-called α-dispersion) of ghost suspensions was definitely observed.

Changes in induced polarization associated with the sorption of sodium, lead, and zinc on silica sands

Low-frequency dielectric spectroscopy can be measured in terms of a conductance and a phase lag between the electrical current and the electrical field. This conductance and phase lag can be written as into a complex conductivity with both an in-phase and quadrature components that are frequency dependent. In sands, the low-frequency (10mHz–40kHz) spectra of the complex conductivity are dominated by the polarization of the electrical double layer (especially the internal part of the electrical double layer called the Stern layer) and the Maxwell–Wagner polarization (typically above 100Hz). We present a polarization that is able to explain the complex conductivity spectra including the grain size distribution, the porosity, and the complexation of the mineral surface with the ions of the pore water. To test this model, we investigate the sorption of various cations (Na, Pb, Zn) characterized by different affinities with the surface of silica. Sand column experiments were carried out to see the change in the complex conductivity during the advective/dispersive transport of a lead nitrate solution and a zinc sulfate solution, replacing a sodium chloride solution in the pore space of the sand. The complex conductivity model is able to explain the change of the phase over time.

Correcting the polarization effect in very low frequency dielectric spectroscopy

Polarization impedance appears at the interface between electrodes and ionic solutions and is a major source of errors in dielectric spectroscopy measurements. This work presents a simple, robust and automated methodology for measuring and analysing the polarization impedance of non-dispersive electrolytes, with a focus on the very low frequency domain from 1 Hz and up. The accuracy of the method is demonstrated by comparing the corrected dielectric permittivity and conductivity of various electrolytes either with their nominal values or with measurements taken with other high precision measuring devices. The dependence of the polarization impedance on several parameters, such as ionic concentration, applied voltage and separation distance between the electrodes, is also presented. For colloidal suspensions, it is argued that a modified protocol of the substitution method is needed due to several shortcomings occurring only in the very low frequency domain. Such a protocol is presented and tested on suspensions of live E. coli cells. As opposed to most of the existing methodologies for polarization removal, the proposed protocol makes no assumptions on the behaviour of the polarization impedance. This could potentially lead to the quantitative resolution of the α-dispersion of live cells in suspension.

Low-Frequency Dielectric Dispersion and Impedance Spectroscopy of lead-free (Na$_{0.5}$Bi$_{0.5}$)TiO$_3$(NBT) Ferroelectric Ceramics

Low-Frequency Dielectric Dispersion and Impedance Spectroscopy of lead-free (Na$_{0.5}$Bi$_{0.5}$)TiO$_3$(NBT) Ferroelectric Ceramics

Impact of the CMP process on the electrical properties of ultra low k porous SiOCH

The impact of chemical mechanical polishing (CMP) on SiOCH films (thickness = 300 nm) for the 32–45 nm node Cu-interconnect process is investigated by low-frequency dielectric spectroscopy and thermally stimulated depolarization current (TSDC). After CMP process, the dielectric permittivity is degraded of about 25% in the whole range of the investigated frequency (10 −1 Hz–100 kHz). In a same way, the dielectric losses tan δ increase at the lowest frequencies. An annealing (300 °C during 20 min) carried out after CMP induces a reduction of the dielectric permittivity without however reaching the value of initial as-deposited material. In agreement with other published papers focusing on the damage caused by the CMP, OH bonding and water adsorption due to surfactants explain the degradation of these dielectric properties. The identification of OH bonds and an increase in the intensity of CH x in the 2800–3050 cm −1 range after CMP seems to confirm this point. The moderate temperature of annealing, used to restore layers and to avoid the degradation of copper lines, suppresses the physisorbed water but not the chemisorbed water. TSDC measurements confirm that dipolar relaxation, due to water in the material, result in a peak of relaxation at a temperature around 175 °C.

Dynamics of Nanodomains in Epitaxial Thin-Film PbZr0.65Ti0.35O3

Epitaxial thin films of rhombohedral perovskite ferroelectric PbZr0.65Ti0.35O3 were grown on MgO and LaAlO3 substrates using La0.5Sr0.5CoO3 bottom electrode. Presence of ferroelectric nanodomains was evidenced by piezoresponse force microscopy. Dynamics of the nanodomains was experimentally studied using low-frequency dielectric spectroscopy in a broad range of conditions. In the dynamic response, the deviation from the Rayleigh law, hysteresis, and dependence on temperature, frequency, and time are revealed. A fast change of the nanodomain configuration at small fields, clamping of nanodomains at the film-electrode interfaces, and reversible motion of the domain walls are suggested to be responsible for these peculiarities.

Infrared and THz Soft-Mode Spectroscopy of (Ba,Sr)TiO3 Ceramics

We performed a study of the temperature dependence of the dielectric response of (Ba,Sr)TiO 3 (BST) ceramics for the whole composition range in a wide frequency range by means of Fourier transform infrared, time-domain THz, microwave and low-frequency dielectric spectroscopy. Room-temperature spectra of the paraelectric dielectric response were compared with the results of first-principle simulations within the effective Hamiltonian approach with a good semi-quantitative agreement. It is shown that in the paraelectric phase away from the transition temperature, the complex THz soft mode, consisting of two overlapping heavily damped oscillators, fully accounts for the low-frequency dielectric properties. However, close to T C additional central-mode type dispersion, apparently caused by the pre-transitional polar clusters, is to be expected in the microwave dielectric spectra.

Phase Transitions and Characterization in a Chiral Smectic-AdeVries Liquid Crystal by Low-Frequency Dielectric Spectroscopy

Low-frequency (10 Hz–6.5 MHz) dielectric investigations are carried out in Smectic-AdeVr phase exhibited by a chiral Liquid Crystal molecule viz., TSiKN65F. Phase transition temperature determined by dielectric method agrees with TM and DSC. LF dielectric study revealed two relaxations in phase, i.e., a Low-frequency sluggish LF-mode and a High-frequency fast HF-mode of dipole reorientation. Dynamics estimated through slope of (T) infers faster HF-mode by three orders. The Arrhenius shift of HF-mode infers an activation energy of 0.72 eV. Influence of field on LF mode is studied. Off-centered dielectric dispersion is analyzed through Cole–Davidson equation. Trends of static permittivity (ϵo), high-frequency permittivity (ϵ∞), dielectric increment Δϵ, and α-parameter studied from Cole–Cole plots are explained.

Collective charge excitations below the metal-to-insulator transition inBaVS3

The charge response in barium vanadium sulfide $({\text{BaVS}}_{3})$ single crystals is characterized by dc resistivity and low-frequency dielectric spectroscopy. A broad relaxation mode in the megahertz range with a huge dielectric constant of $\ensuremath{\approx}{10}^{6}$ emerges at the metal-to-insulator phase transition ${T}_{\text{MI}}\ensuremath{\approx}67\text{ }\text{K}$, weakens with lowering temperature, and eventually levels off below the magnetic transition ${T}_{\ensuremath{\chi}}\ensuremath{\approx}30\text{ }\text{K}$. The mean relaxation time is thermally activated in a manner similar to the dc resistivity. These features are interpreted as signatures of the collective charge excitations characteristic for the orbital ordering that gradually develops below ${T}_{\text{MI}}$ and stabilizes at long-range scale below ${T}_{\ensuremath{\chi}}$.