Ferroelectric and dielectric characterization studies on relaxor- and ferroelectric-like strontium-barium niobates

Ferroelectric domain structure evolution induced by an external electric field was investigated by means of nematic liquid crystal (NLC) method in two strontium-barium niobate single crystals of nominal composition: Sr_{0.70}Ba_{0.30}Nb_{2}O_{6} (SBN:70 - relaxor) and Sr_{0.26}Ba_{0.74}Nb_{2}O_{6} (SBN:26 - ferroelectric). Our results provide evidence that the broad phase transition and frequency dispersion that are exhibited in SBN:70 crystal have a strong link to the configuration of ferroelectric microdomains. The large leakage current revealed in SBN:26 may compensate internal charges acting as pinning centers for domain walls, which gives rise to a less restricted domain growth similar to that observed in classical ferroelectrics. Microscale studies of a switching process in conjunction with electrical measurements allowed us to establish a relationship between local properties of the domain dynamics and macroscopic response i.e., polarization hysteresis loop and dielectric properties.Comment: 10 pages, 7 figure

Dielectric and conductivity relaxation in mixtures of glycerol with LiCl

We report a thorough dielectric characterization of the alpha relaxation of glass forming glycerol with varying additions of LiCl. Nine salt concentrations from 0.1 - 20 mol% are investigated in a frequency range of 20 Hz - 3 GHz and analyzed in the dielectric loss and modulus representation. Information on the dc conductivity, the dielectric relaxation time (from the loss) and the conductivity relaxation time (from the modulus) is provided. Overall, with increasing ion concentration, a transition from reorientationally to translationally dominated behavior is observed and the translational ion dynamics and the dipolar reorientational dynamics become successively coupled. This gives rise to the prospect that by adding ions to dipolar glass formers, dielectric spectroscopy may directly couple to the translational degrees of freedom determining the glass transition, even in frequency regimes where usually strong decoupling is observed.Comment: 8 pages, 7 figure

Equivalent Circuit Modeling of the Dielectric Loaded Microwave Biosensor

This article describes the modeling of biological tissues at microwave frequency using equivalent lumped elements. A microwave biosensor based on microstrip ring resonator (MRR), that has been utilized previously for meat quality evaluation is used for this purpose. For the first time, the ring-resonator loaded with the lossy and high permittivity dielectric material, such as; biological tissue, in a partial overlay configuration is analyzed. The equivalent circuit modeling of the structure is then performed to identify the effect of overlay thickness on the resonance frequency. Finally, the relationship of an overlay thickness with the corresponding RC values of the meat equivalent circuit is established. Simulated, calculated and measured results are then compared for validation. Results are well agreed while the observed discrepancy is in acceptable limit

Fast regeneration of activated carbons saturated with textile dyes: Textural, thermal and dielectric characterization

This study presents an investigation for comparing the regeneration process of two activated carbons saturated with Basic Blue 9 (BB9) and Acid Blue 93 (AB93) using conventional (250–500 °C) and microwave heating (100–300 W). The effect of the textile dye used on the regeneration performance was analyzed by determining their dielectric properties using the perturbation cavity method from 20 to 600 °C and by TG/DTG analysis. The efficacy of the regenerated carbons was investigated by their physical properties characterized by pore structural analysis using N2 adsorption isotherms. Results showed only 3 min are required by microwaves to achieve similar textural parameters obtained by conventional heating at 190 min. The results indicate that the adsorbate plays a determining role on the regeneration efficiency as results of their interaction with the adsorbent, being easily regenerated when AB93 is the adsorbate. The adsorption capacity of microwave regenerated samples for AB93 and BB9 was 192–240 and 154–175 mg/g, respectively. Additionally, the equilibrium isotherms were simulated using the Langmuir and Freundlich isotherms models and the results suggest the textile dye removal is achieved on multilayer adsorption

Dielectric characterization of the BiFe0.5Cr0.5O3 ceramics

Dielectric properties of the BiFe0.5Cr0.5O3 ceramics synthesized under high pressure were investigated in a broad frequency range (20 Hz – 1 GHz) between 200 and 500 K. It was revealed that the ceramics exhibit electrical conductivity above 300 K. Below 300 K, a dielectric dispersion caused by ferroelectric domains was observed. It was found that the conductivity follows the Almond–West law, which allowed us to determine a DC contribution (σDC). From the σDC values obtained at different temperatures, the activation energy (EA = 0.302 ± 0.006 eV) was calculated using the Arrhenius law.publishe

Dielectric Characterization of Coastal Cartilage Chondrocytes

BACKGROUND: Chondrocytes respond to biomechanical and bioelectrochemical stimuli by secreting appropriate extracellular matrix proteins that enable the tissue to withstand the large forces it experiences. Although biomechanical aspects of cartilage are well described, little is known of the bioelectrochemical responses. The focus of this study is to identify bioelectrical characteristics of human costal cartilage cells using dielectric spectroscopy. METHODS: Dielectric spectroscopy allows non-invasive probing of biological cells. An in house computer program is developed to extract dielectric properties of human costal cartilage cells from raw cell suspension impedance data measured by a microfluidic device. The dielectric properties of chondrocytes are compared with other cell types in order to comparatively assess the electrical nature of chondrocytes. RESULTS: The results suggest that electrical cell membrane characteristics of chondrocyte cells are close to cardiomyoblast cells, cells known to possess an array of active ion channels. The blocking effect of the non-specific ion channel blocker gadolinium is tested on chondrocytes with a significant reduction in both membrane capacitance and conductance. CONCLUSIONS: We have utilized a microfluidic chamber to mimic biomechanical events through changes in bioelectrochemistry and described the dielectric properties of chondrocytes to be closer to cells derived from electrically excitably tissues. GENERAL SIGNIFICANCE: The study describes dielectric characterization of human costal chondrocyte cells using physical tools, where results and methodology can be used to identify potential anomalies in bioelectrochemical responses that may lead to cartilage disorders

Dielectric sensitization of zeolitic imidazolate framework-8 (ZIF-8) nanopowder.

Metallo-organic complexes are a class of materials that are increasingly used in sensory applications. Zeolitic imidazolate frameworks (ZIFs) are their subclass that are topologically isomorphic with zeolites. The porosity of the crystals and their chemical structure, as well as their thermal and chemical stability, make some of these materials (ZIFs) very suitable for making sensors. The large specific area of micro and nano particles is an important parameter for sensor applications. Despite the fact that the dielectric characterization of powders in the RF domain was neglected in scientific works, this method can have great practical importance. This paper presents the results of the dielectric characterization of the ZIF-8 nanopowder in the frequency range of 24 Hz to 24 KHz. The results indicate that the presence of evaporation of water, ethanol and methanol leads to major changes in the dielectric permittivity of ZIF-8 nanopowder

Conducting polymer coated fabrics for potential applications in microwave frequencies : a study of electromagnetic properties

The microwave reflection, transmission and complex permittivity of paratoluene-2-sulfonic acid doped conducting polypyrrole (PPy/pTSA) coated Nylon-Lycra textiles in the 1-18 GHz frequency were investigated. The real part of permittivity increased with polymerization time and dopant concentration, reaching a plateau at certain dopant concentration and polymerization time. The imaginary part of permittivity showed a frequency dependent change throughout the tested range. All the samples had higher values of absorption than reflection. The total electromagnetic shielding effectiveness exceeded 80% for the highly pTSA doped samples coated for 3 hours