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Search Results: 1 - 10 of 6044 matches for " electrical spectroscopy. "
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Frequency Dependence of Atomic Diffusivity and Electrical Properties of Gum Arabic/Graphite Composite  [PDF]
Bilquis Ibrahim Adham, Hatim Mohamed El-Khair, Mohamed Ahmed Siddig
Journal of Materials Science and Chemical Engineering (MSCE) , 2015, DOI: 10.4236/msce.2015.39004
Abstract: In this study, Gum Arabic (GA)/Graphite (Gr) composite material was prepared using solid state reaction method. The FTIR peaks obtained were referred to the binding of Gr with the active groups in GA, such as NH2, COOH, CHO, CNC (alkyl amine) and C=CH (aromatic monosubstitution). Atomic diffusivity of Gr in GA was calculated using simple model and was found to varied randomly. This randomness might be due to the attachment of Gr with different active groups of GA. The addition of Gr results in improvement of the conductivity of GA to a far extend as it reaches the semiconductor range. The random variation in conductivities of the samples can be attributed to the effect of high frequency range, where the effect of phonon-electron is dominant. The samples subjected to the impedance spectroscopy (IS) for second and third time were acquired different diffusivities as well as conductivities. Such variations might indicate that IS was a processing technique similar to thermal treatment since it boosted the Gr atomic diffusion.
Electrical and Dielectric Characterization of Na0.5Li0.5Zr2(PO4)3  [PDF]
Umaru Ahmadu, Abubakar Ohinoyi Musa, Tomas Salkus, Kasim Uthman Isah
Open Journal of Physical Chemistry (OJPC) , 2011, DOI: 10.4236/ojpc.2011.13013
Abstract: Na0.5Li0.5Zr2(PO4)3has been synthesized by solid state reaction and characterized by thermogravimetry/ differential thermal analyses (TGA/DTA) in the temperature range 300 - 1573 K. X-ray diffraction measure- ments have been carried out to determine the phase of the composition and scanning electron microscopy (SEM) for microstructure evaluation. Impedance spectroscopy at different temperatures (310 - 600 K) and frequencies (300 kHz - 1 GHz) have been carried out and the dielectric relaxation behaviour was determined under the same conditions. A dc conductivity maximum value of 0.25 S/m at 580 K was observed. However, the mixed alkali effect was not observed. The material exhibited relaxation behaviour with a peak in the dielectric permitivity at 469 K. There were no structural transformations observed.
Characterization of Electrical Behavior of Ba5HoTi3V7O30 Ceramic Using Impedance Analysis  [PDF]
Kiran Kathayat, Anuradha Panigrahi, Arvind Pandey, Susmita Kar
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.36056
Abstract: Polycrystalline sample of Ba5HoTi3V7O30 was prepared using solid-state reaction technique. X-ray structural analysis indicated a single-phase formation with orthorhombic structure. Microstructural study by SEM showed non-uniform distribution of grains over the surface of the sample. Impedance and modulus spectroscopy studies were carried out, as functions of frequency (42 Hz - 5 MHz) and temperature (RT-773K). The Nyquist plots clearly showed the presence of both bulk and grain boundary effect in the compound. Electrical phenomena in the material can appropriately be modeled in terms of an equivalent circuit with R, C and CPE in parallel. The fitting procedure used here allows us to determine the value of R and C with good precision. Here R2 and R3 correspond to the resistance contributed from the grain boundary and bulk, respectively. C1 and C2 correspond to the capacitance contributed from the grain boundary and bulk, respectively. The real part of electrical modulus shows that the material is highly capacitive. The asymmetric peak of the imaginary part of electric modulus M″, predicts a non Debye type relaxation. The activation energy of the compound (calculated both from impedance and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers.
Effects of Gamma Irradiation on the Kinetics of the Adsorption and Desorption of Hydrogen in Carbon Microfibres  [PDF]
Cesar Mota, Mario Culebras, Andrés Cantarero, Antonio Madro?ero, Clara Maria Gómez, Jose María Amo, Jose Ignacio Robla
Advances in Materials Physics and Chemistry (AMPC) , 2013, DOI: 10.4236/ampc.2013.32021
Abstract:

In this study, three types of carbon fibres were used, they were ex-polyacrylonitrile carbon fibres with high bulk modulus, ex-polyacrylonitrile fibres with high strength, and vapour grown carbon fibres. All the samples were subjected to a hydrogen adsorption process at room temperature in an over-pressured atmosphere of 25 bars. The adsorption process was monitored through electrical resistivity measurements. As conditioning of the fibres, a chemical activation by acid etching followed by γ-ray irradiation with 60Co radioisotopes was performed. The surface energy was determined by means of the sessile drop test. Both conditioning treatments are supplementary; the chemical activation works on the outer surface and the γ-irradiation works in the bulk material as well. Apparently, the most significant parameter for hydrogen storage is the crystallite size. From this point of view, the most convenient materials are those with small grain size because hydrogen is accumulated mainly in the grain boundaries.

Grain size effect on the electrical response of SnO2 thin and thick film gas sensors
Savu, Raluca;Ponce, Miguel Adolfo;Joanni, Ednan;Bueno, Paulo Roberto;Castro, Miriam;Cilense, Mario;Varela, José Arana;Longo, Elson;
Materials Research , 2009, DOI: 10.1590/S1516-14392009000100010
Abstract: porous nano and micro crystalline tin oxide films were deposited by rf magnetron sputtering and doctor blade techniques, respectively. electrical resistance and impedance spectroscopy measurements, as a function of temperature and atmosphere, were performed in order to determine the influence of the microstructure and working conditions over the electrical response of the sensors. the conductivity of all samples increases with the temperature and decreases in oxygen, as expected for an n-type semiconducting material. the impedance plots indicated the existence of two time constants related to the grains and the grain boundaries. the nyquist diagrams at low frequencies revealed the changes that took place in the grain boundary region, with the contribution of the grains being indicated by the formation of a second semicircle at high frequencies. the better sensing performance of the doctor bladed samples can be explained by their lower initial resistance values, bigger grain sizes and higher porosity.
Prepara??o e caracteriza??o elétrica de sensores de metanol à base de nanocompósitos híbridos de polipirrol/nanopartículas metálicas
Oliveira, Helinando P. de;Oliveira, Ariadne H. P. de;Tavares, Ginetton F.;Albuquerque Jr, José J. F.;Andrade, César A. S.;
Polímeros , 2010, DOI: 10.1590/S0104-14282010005000042
Abstract: in this study, hybrid composites of gold nanoparticles and polypyrrole (aunps-ppy) were manufactured by chemical polymerization of the pyrrole monomer on the surface of metal nanoparticles, which were then incorporated in a poly(vinyl alcohol) (pva) matrix to be exploited in sensing technologies for detecting methanol. the preparation conditions were optimized to maximize sensitivity, allowing for the determination of relative concentrations of methanol molecules in binary mixtures of methanol/ethanol. this was carried out using the electrical response of the sensor, which depends on the dielectric constant of the volatile organic compounds.
The electrical signature of rock samples exposed to hydrostatic and triaxial pressures
H. Heikamp,G. Nover
Annals of Geophysics , 2001, DOI: 10.4401/ag-3595
Abstract: The electrical signature of sedimentary (carbonate) and crystalline rock samples was studied in hydrostatic and triaxial pressure experiments up to 300 MPa. The aim was to establish a relation between an electrical signal stimulated by an external pressure acting on the sample and the mechanical stability of the rock. Natural open fractures tend to be closed under hydrostatic pressure conditions, whereas in triaxial pressure experiments new fractures are generated. These contrary processes of either decrease or increase in crack density and geometry, cause a decrease or increase in the inner surface of the sample. Such pressure induced variations in pore geometry were investigated by an interpretation and modelling of the frequency dependence of the complex electrical conductivity. In a series of hydrostatic pressure experiments crack-closure was found in the electrical signature by a decrease of the model capacitor C being related to crack geometry. This capacitor increases in the triaxial experiments where new fractures were formed.
Elevated temperature induced dispersion phenomena in Ba 1-xNaxTi1-xNbxO3
W. B?k,F. Starzyk,C. Kajtoch,E. Nogas - ?wikiel
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: of this paper was to investigate features of the dispersion of dielectric permittivity induced by elevated temperature (473K-723K) in polycrystalline solid solution of Ba1-xNaxTi1-xNbxO3 (for x=0.3 and x=0.4).Design/methodology/approach: used to perform this purpose was dielectric spectroscopy application to measure dielectric and electric parameters within the frequency range (20Hz-1MHz).Findings: Analysis of temperature and frequency dependences of real (ε’) and imaginary (ε”) parts of dielectric permittivity had pointed out on relaxor type of dielectric behaviour for both investigated samples in paraelectric phase. The thermal activation energy values of ac conductivity (for 100Hz) are similar to those of semiconductors. Values of ε’ for both materials (x=0.3, x=0.4) are consistent with literature quotations. Thus the polarisation behaviour of our materials seems to be similar to those described in the literature. Different behaviour of dielectric energy losses is postulated as originating from differences of samples microstructure.Research limitations/implications: Further investigations should be carried out in the range of low temperatures (down to 100K) and within a broaden frequency range (up to 1.8GHz) in order to establish the influence of chemical structure on ferroelectric-paraelectric phase transition.Originality/value: Dielectric properties for two new material prepared from nanopowders of BaTiO3 and NaNbO3 were described.
Characterization of Ba1-xNaxTi1-xNbxO3
W. B?k
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The purpose of this paper was characterization of electric properties of polycrystalline nanograin solidsolution of Ba1-xNaxTi1-xNbxO3, x = 0.65 (BNTN65) within the temperature range 153 K-573 K.Design/methodology/approach: The dielectric spectroscopy method (DSM) has been applied to measuredielectric and electric parameters within frequency range from 20 Hz to 1 MHz and within the temperature rangeof diffused ferroelectric – paraelectric transition and above within paraelectric state.Findings: Analysis of temperature and frequency dependences of real (ε’) and imaginary (ε”) parts of dielectricpermittivity and electric modulus provided the new details about specific features of paraelectric properties ofceramic BNTN65 sample. They involve weak relaxational diffused processes as well as dielectric losses. Specifictwo steps increase of ε’ values turned out to be frequency dependent and of thermal activated character.Research limitations/implications: Above specified new details of polarizability of paraelectric phase forceramic sample should be treated as a base for new modelling approach and quantitative description of polarclusters dependence on temperature and frequency.Originality/value: For the first time, details of polarizability of paraelectric phase, which are temperature andfrequency dependent in such specific manner were described.
Parametrisation of interdigit comb capacitor for dielectric impedance spectroscopy
F. Starzyk
Archives of Materials Science and Engineering , 2008,
Abstract: Purpose: The purpose of this paper was to collect full description of interdigit capacitor (IDC) used in interdigitdielectrometry and to point out on the way how it should be applied in practice.Design/methodology/approach: The full graphical representation of IDC geometry and its descriptionwas demonstrated and described. Capacity of IDC and electric potential distribution as well as charge densitydistribution on flat comb electrodes were demonstrated.Findings: Though the analytical formulas of effective IDC capacity and potential distribution are complicated, thepractical application of IDC in dielectric measurements is much simpler than those of flat or cylindrical capacitors.Research limitations/implications: Practical limitations were formulated and specified together with their meanings.Practical implications: Universality of measuring procedure with IDC application was pointed out and completed.Originality/value: Complete description of IDC parameters will make easier for potential investigator frommany scientific disciplines to see how one have to understand and apply in practice IDC dielectrometry techniqueas well as potentially make the IDC parameter optimal for given application.
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