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Impedance Spectroscopy Measurements (impedance + spectroscopy_measurement)
Selected AbstractsStudy of the activation process of Mg dopant in GaN:Mg layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2006B. Paszkiewicz Abstract GaN:Mg layers with different concentration of Mg dopant were grown by metalorganic vapour phase epitaxy. The incorporation of Mg was verified by secondary ion mass spectroscopy. In order to dissociate Mg-related complexes and thus electrically activate the acceptor dopant, the as-grown layers were annealed in pure N2 at ,800 °C for 30 minutes. The influence of the post-growth annealing on the layer properties was studied by photoluminescence (PL) and impedance spectroscopy. Impedance spectroscopy measurement showed that the annealed samples reveal higher charge concentrations and lower sheet resistance. Moreover, the relaxation time of hole traps decreased in annealed samples by one order of magnitude compared to as-grown samples. The changes in the electrical properties have been correlated with the changes in the PL spectra. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conductivity and characterization of polyurea electrolytes with carboxylic acidJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2003Shao-Ming Lee Abstract Polyurea, which was synthesized from 4,4,-diphenylmethane diisocyanate, Jeffamine-ED2001 (weight-average molecular weight: 2000), and 3,5-diaminobanzoic acid (DABA) were doped with lithium perchlorate (LiClO4) as the polyelectrolyte. Differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and 7Li magic-angle spinning (MAS) solid-state NMR were used to monitor changes in the morphology of polyurea electrolytes corresponding to the concentration of LiClO4 dopants. DSC showed the glass-transition temperature of the hard and soft segments increases with salt concentration. FTIR indicated the carboxylic group of DABA coordinates with the Li+ ion, and the ordered hydrogen-bonded urea carbonyl groups are destroyed when the salt concentration exceeds 0.5 mmole of LiClO4 (gPUrea),1. The 7Li MAS solid-state NMR investigation of the polyurea electrolytes revealed the presence of two Li+ environments at lower temperature. Impedance spectroscopy measurements showed that the conductivity behavior followed the Arrhenius equation, and the maximum conductivity occurred when the crystalline structure of polyurea was disrupted. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 4007,4016, 2003 [source] A New Indirect Electroanalytical Method to Monitor the Contamination of Natural Waters with 4-Nitrophenol Using Multiwall Carbon NanotubesELECTROANALYSIS, Issue 9 2009Cruz Moraes, Fernando Abstract The electrochemical detection of the hazardous pollutant 4-nitrophenol (4-NP) at low potentials, in order to avoid matrix interferences, is an important research challenge. This study describes the development, electrochemical characterization and utilization of a multiwall carbon nanotube (MWCNT) film electrode for the quantitative determination of 4-NP in natural water. Electrochemical impedance spectroscopy measurements showed that the modified surface exhibits a decrease of ca. 13 times in the charge transfer resistance when compared with a bare glassy carbon (GC) surface. Voltammetric experiments showed the possibility to oxidize a hydroxylamine layer (produced by the electrochemical reduction of 4-NP on the GC/MWNCT surface) in a potential region which is approximately 700,mV less positive than that needed to oxidize 4-NP, thus minimizing the interference of matrix components. The limit of detection for 4-NP obtained using square-wave voltammetry (0.12,,mol L,1) was lower than the value advised by EPA. A natural water sample from a dam located in São Carlos (Brazil) was spiked with 4-NP and analyzed by the standard addition method using the GC/MWCNT electrode, without any further purification step. The recovery procedure yielded a value of 96.5% for such sample, thus confirming the suitability of the developed method to determine 4-NP in natural water samples. The electrochemical determination was compared with that obtained by HPLC with UV-vis detection. [source] Fabrication and Electrochemical Properties of Epitaxial Samarium-Doped Ceria Films on SrTiO3 -Buffered MgO SubstratesADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Simone Sanna Abstract Thin films of samarium-oxide-doped (20,mol%) ceria (SDC) are grown by pulsed-laser deposition (PLD) on (001) MgO single-crystal substrates. SrTiO3 (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite-structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400,775,°C) in a wide range of oxygen partial pressure (pO2) values (10,25,1,atm) in order to separate ionic and electronic conductivity contributions. At 700,°C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7,×,10,2,S cm,1, down to pO2 values of about 10,15,atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation-reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure. [source] Fiber-Embedded Electrolyte-Gated Field-Effect Transistors for e-TextilesADVANCED MATERIALS, Issue 5 2009Mahiar Hamedi Electrolyte-gate organic field-effect transistors embedded at the junction of textile microfibers are demonstrated. The fiber transistor operates below 1 V, and delivers large current densities. The transience of the organic thin-film transistor's current and the impedance spectroscopy measurements reveal that the channel is formed in two steps. [source] Preparation and study of cellulose acetate membranes modified with linear polymers covalently bonded to Starburst polyamidoamine dendrimersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008J. Ledesma-García Abstract Novel ion-selective membranes were prepared by means of the noncovalent modification of a cellulose acetate (CA) polymer with either poly(ethylene- alt -maleic anhydride) or poly(allylamine hydrochloride) chains covalently linked to Starburst amine-terminated polyamidoamine (PAMAM) dendrimers generations 4 and 3.5, respectively. Linear polymer incorporation within the porous CA membrane was performed with mechanical forces, which resulted in modified substrates susceptible to covalent adsorption of the relevant dendritic materials via the formation of amide bonds with a carbodiimide activation agent. The membranes thus prepared were characterized by chemical, physical, and spectroscopic measurements, and the results indicate that the dendrimer peripheral functional groups were the species that participated in the ion-exchange events. The prepared materials were also evaluated for their ion-exchange permeability with sampled current voltammetry experiments involving cationic and anionic species {[Ru(NH3)6]3+ and [Fe(CN6)]3,, respectively} as redox probe molecules under different pH conditions. As expected, although permeability was favored by opposite charges between the dendrimer and the electroactive probe, a clear blocking effect took place when the charge in the dendritic polymer and the electroactive complex was the same. Electrochemical impedance spectroscopy measurements, on the other hand, showed that the PAMAM-modified membranes were characterized by good selectivity and low resistance values for multivalent ions compared to a couple of commercial ion-exchange membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Physical Modeling and Electrodynamic Characterization of Dielectric Slurries by Impedance Spectroscopy (Part II)JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Vladimir Petrovsky Electrical characterization of dielectric slurries, as 0,3 composite systems, can provide valuable information on the dielectric properties of suspended particles. A new approach developed in our laboratory is based on impedance spectroscopy measurements of the slurries containing dispersed dielectric powders. Dielectric constants of the particles are determined through analysis of the low-frequency section of the impedance spectra. It was shown previously that this approach allows accurate and reliable measurement of dielectric constant of particles (,: ,100,2000) using host liquids (,: ,10,65). This study addresses the validation of this new method with physical model experiments using millimeter-sized sintered BaTiO3 model samples suspended in the liquid. Impedance spectra of barium titanate powder slurries were compared with the spectra of the model samples containing macroscopic cubes prepared by sintering of the same starting powder. This comparison shows a good agreement between the impedance spectra of powder and bulk BaTiO3 and validates the reliability of the new method to determine the dielectric constant of particulate materials. [source] Dielectric properties of Li doped Li-Nb-O thin filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007G. Perentzis Abstract Lithium niobate LiNbO3 was prepared as a thin film layered structure deposited on stainless steel substrate using e-gun evaporation. The Li doping was provided for by the formation of Li-Nb-O/Li/LiNb-O sandwich structure and annealing at about 250 °C. AC impedance spectroscopy measurements were performed on the samples at temperatures from the interval between 28 and 165 °C and in a frequency range of 10,3 to 106 Hz. Using the values Z , and Z , at different frequencies, the dielectric parameters , parts of the complex permittivity ,, and ,, and loss tangent tan , were calculated. The results prove validity of the proposed equivalent circuit containing parallel RC elements connected in series where the first RC element represents the bulk of material and the second RC element belongs to the double layer at the metal interface. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electrical transport properties of aliovalent cation-doped CeO2ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Mark C. Pearce Abstract We report the comparative electrical properties of monovalent (Na+), divalent (Ca2+, Sr2+), trivalent (In3+, La3+) and coupled substitution of divalent and trivalent (Ca2+ + Sm3+) cation-doped CeO2. The investigated samples were prepared by solid-state reaction (ceramic) using the corresponding metal oxides and salts in the temperature range 1000,1600 °C in air. Powder X-ray diffraction (PXRD), laser particle size analysis (LPSA), scanning electron microscopy (SEM), and ac impedance spectroscopy measurements were employed for structural, morphology, and electrical characterization. PXRD studies reveal the formation of single-phase cubic fluorite-type structures for all investigated samples except those doped with In3+. The variation of lattice parameters is consistent with ionic radii (IR) of the dopant metal ions, with the exception of Na+ -doped CeO2. Our attempt to substitute In3+ for Ce4+ in CeO2 using both ceramic and wet chemical methods was unsuccessful. Furthermore, diffraction peaks attributed to CeO2 and In2O3 were observed up to sintering conditions of 1600 °C. Among the single-phase compounds investigated, Ce0.85Ca0.05Sm0.1O1.9 exhibits the highest bulk conductivity of 1.3 × 10,3 S/cm at 500 °C with activation energy of 0.64 eV in air. The electrical conductivity data obtained for Ce0.85Ca0.05Sm0.1O1.9 in air and Ar were found to be very similar over the investigated temperature range, indicating the absence of p-electronic conduction in the high oxygen partial pressure (pO2) range which is consistent with literature reported on Sm-doped CeO2. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||