Papers by Keyword: Dielectric Spectroscopy

Abstract: Bulk specimens of Bi₂Ca_2-xCe_xCoO₆ (x = 0.00, 0.20) were prepared in pure phase form using co-precipitation method. The monoclinic structure of all samples is revealed via X-Ray Diffraction (XRD) analysis. The crystallite size, lattice constant, lattice strain, and volume of the unit cell were all determined using XRD analysis. On sintered at 750°C for 2 hours, the average crystallite size was 32-38nm. The precision analyzer was used to determine the loss tangent tan (δ), dielectric constant (ε'), AC conductivity (σ_ac) in the 20Hz-3MHz range. The conduction process of electrical conductivity was also investigated utilizing the Jonscher Power Law.

Abstract: New scheelite type Cd_1-3xDy_2x[]_xMoO₄ solid solution, where 0.0098 ≤ x ≤ 0.2 and [] denotes the cationic vacancies, was investigated by using UV-vis-NIR and dielectric spectroscopies at room temperature and in the temperature range 77-400 K, respectively. These studies showed the optical band gap energy E_g above 3.4 eV and relative low dielectric permittivity: ε_r ~ 6.0, 9.5, 7.0 and 8.2 for the x parameter 0.0098, 0.0839, 0.1667 and 0.2000, respectively. ε_r slightly decreases with increasing frequency and slightly increases at higher temperatures. All samples showed the maximum permittivity in the temperature range of 250-350 K. The loss tangent exhibited similar behaviour and its maximum value did not exceed 0.25. These results are discussed in a context of the shallow trap levels and the Maxwell-Wagner model.

Abstract: The quantitative analysis of experimental results of research thermostimulated currents in crystals Bi₁₂SiO₂₀ (BSO) is lead carried out. Parameters of the capture centers in crystals BSO are determined.

Abstract: Many physical effects, such as dc conductivity and percolation, depend on the morphology of the silicate structure and its relationship to adsorbed water. These effects play an important role in numerous technological applications, in geology, oil-extracting industry, and other practical fields. In this study, all the samples: natural montmorillonite, kaolinite, and сlinoptilolite with different exchangeable cations in their structures, – were stored in ambient air humidity. The investigation was carried by using two separate techniques, namely Dielectric Spectroscopy and a fractal analysis of electron micrographs. The aims of this work were to analyze the complex relaxation behavior of the relaxation process in temperature range –70°C ÷ +70°C and to determine the fractal dimensions of silicates from the dielectric response at percolation. Dielectric measurements in the frequency range of 1 Hz ÷ 1 MHz were performed using a BDS 80 Dielectric Spectrometer based on an Alpha Impedance Analyzer (Novocontrol). The micrographs were analyzed using a special Matlab based program. The analysis of aspects of the dielectric relaxation spectra related to percolation was used for the determination of the numerical characteristics of geometric heterogeneity of natural silicates. The percolation temperatures of the studied samples were determined. The percolation phenomenon in the silicates is related to the transfer of the electric excitation within the developed network of open pores due to the migration of protons and ions along the surface of connected pores on the outer surfaces of the granules. The analysis of these processes allows one to extract the fractal dimensions associated with the migration of charge carriers within the porous medium. Fractal dimensions of the silicates calculated in two ways: from dielectric spectroscopy study and from fractal analysis of the micrographs, – are in good agreement with each other. It was demonstrated that conventional method of the spatial fractal dimension determination using fractal analysis of electron micrographs leads to overestimation in the case of spatial fractal bounded by a surface fractal. The dielectric spectroscopy method is free from such overestimation.

Abstract: In this paper, the dielectric properties of ZnO-Bi₂O₃ based varistor ceramics doped with Li are investigated by Novocontrol wide band dielectric spectrometer. It is found that Lithium is an amphoteric impurity. If the content of Lithium is very low, It will enters into the interstitials and Lithium interstitial is formed as a donor. While with the increase of Lithium content, Zn is replaced with Li and Lithium substitution for Zinc as a acceptor is formed. If the content of Lithium increases further, Lithium interstitial is formed again with the redundant Lithium. Therefore, the concentrations of intrinsic point defects of Zinc interstitial and oxygen vacancy varies with the content of Lithium, which leads to the increase of Schottky barrier at grainboundary with Lithium.

Abstract: This work involves the fabrication of high purity Pb (Zr,Ti)O₃ ferroelectric based in ceramic forms, and a study of the correlation between their compositions and electrical properties. In order to enhance multiferroic characteristics of Pb (Zr,Ti)O₃ ferroelectric based ceramics compound ferrites additives were added and the dielectric property as a function of magnetic field strength. Those are expected to explain multiferroic characteristics (ferroelectric-ferromagnetic coupling interaction) by quantitative evaluation which is the key to understand physical mechanism in coupling interaction to enhance multiferroic characteristics in materials.

Abstract: ESD garments are used to protect sensitive devices from electrostatic discharges that can occur from the normal clothing of the human operators. Over the years, researchers implemented different structures of fabrics that can be used in ESD garments and studied their ESD properties using different methods. The current paper presents the possibility to use the information obtained from dielectric spectroscopy in order to evaluate the fabrics electrostatic charge decay time and investigates the presence of a correlation between the losses factor tan (δ) and the electrostatic charge decay time.

Abstract: The effects of orientation on the segmental dynamics of vulcanized natural rubber have been studied by dielectric relaxation spectroscopy. Morphological changes during the stretching process were also investigated by wide-angle X-ray scattering using a synchrotron radiation. Results reveal that segmental dynamics of NR is affected by uniaxial stretching since a slowing down of the segmental relaxation is achieved. Also, there is evidence of an amorphous/semi-crystalline transition around 300% strain; below this extension, molecular chains show orientation, but no crystallization takes place; while above such strain, the crystalline structure formed limits the segmental dynamics of NR.

Abstract: Crop wet biomass measuring with dielectric spectroscopy is a non-destructive method to quickly and accurately estimate plant biomass in situ. It optimizes the management of agronomists. An electrostatic free-space system was designed and tested to estimate crop wet biomass in situ. It acts as a parallel plate capacitor. The appropriate size of plate of the system is determined through Finite element analysis (FEA). Water is used to make the exclusion of interference at the earlier stage of the experiment, and Wheat is the experiment material. Results from the measuring system showed The Susceptance through the system was strongly correlated with wet biomass. The coefficient of determination (r2) is greater than 0.9.

Abstract: There are two kinds of charges in dielectric materials, one is bound charge, and the other is free charge. Bound charge will introduce dielectric relaxation under applied AC electric field, which will be detected with dielectric spectroscopy. Free carrier will introduce DC conduction through the sample from one electrode to the other under DC electric field. But what can we do to obtain AC and DC properties of dielectric materials at the same time In this paper, dielectric characteristics of ZnO varistor ceramics in a wide range of frequency and temperature are reported. DC conductivity is observed at low frequency and high temperature region and grainboundary Schottky barrier is obtained further. Dielectric loss peaks are observed at high frequency and low temperature region and single grainboundary electric breakdown voltage is calculated. At the end of the paper, the advancing trend of dielectric spectroscopy is discussed.