Search results for "Dielectric spectroscopy"
showing 10 items of 243 documents
Anodic growth of passive layers on steel rebars in an alkaline medium simulating the concrete pores
2006
Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques have been used to study passive layers anodically grown on steel rebars in an aqueous alkaline solution simulating the electrolyte of the concrete pores. Nyquist diagrams recorded by EIS at the different stabilization potentials show a diffusional tail at low frequencies. The analysis of the impedance measurements has been made by means of an equivalent circuit with a Warburg component and within the framework of the point defect model (PDM) theory. It is observed that the calculated concentration of vacancies is a function of the potential in accordance with the theoretical prediction of the PDM.
Improvement of the electrochemical behaviour of Zn-electroplated steel using regenerated Cr(III) passivation baths
2014
[EN] Conversion coatings based on trivalent chromium are more sensitive to the presence of zinc and iron impurities than the chromate formulations. This fact contributes to a decrease in the quality of passivation and to the generation of a significant amount of hazardous liquid waste. Recently, a new eco-innovative process based on Emulsion Pertraction Technology (EPT) is being implemented at industrial scale for selectively removing Zn and Fe from spent passivation baths in order to enhance the lifetime of the Cr (III) baths. In this study, the effect of Zn and Fe removal on the electrochemical behaviour of Zn-electroplated steel samples was evaluated by means of polarisation curves and e…
Broadband Dielectric Spectroscopy of PSN-Rich PMN-PSN Ceramics
2008
The broadband dielectric permittivity of ordered 0.1PMN-0.9PSN and disordered 0.2PMN-0.8PSN ceramics was investigated. The anomaly of dielectric permittivity is clearly seen in the region of 370 K for 0.1 PMN-0.9 PSN at all frequencies. 0.2 PMN-0.8 PSN shows relaxor behaviour with huge frequency dispersion below 350 K. Calculated distribution of relaxation times shows noticeable influence of polar nano regions to the total dielectric spectrum below 320 K with the longest relaxation times edge diverging according to the Vogel-Fulcher law. In 0.1 PMN-0.9 PSN two a little overlapped peaks present in the distribution of relaxation times, influenced by displacive lead motions at high frequencies…
High frequency dielectric relaxation in BaTio3derived materials
1992
Abstract A systematic study of the dielectric relaxation phenomenon has been carried out for ceramics with compositions derived from barium titanate in the frequency and temperature ranges 1 MHz–1 GHz and 250–500 K, respectively. Whatever the composition may be, a minimum of the relaxation frequency and a maximum of the dielectric dispersion appears at each phase transition temperature. The dipole-type relaxation is correlated to coherent displacements of the ions in the octahedron sites ordered either along chains or in 3D-lattice.
Anomalous Broad Dielectric Dispersion of 0.4PZN-0.3PSN-0.3PZN Relaxor Ceramics at Lower Temperatures
2006
Dielectric properties of 0.4PbZn1/3Nb2/3O3-0.3PbSc1/2Nb1/2O3-0.3PbMg1/3Nb2/3O3- (0.4PZN- 0.3PSN-0.3PMN) ceramics are presented for 200 < T < 500 K and 20 Hz < ν < 1 MHz. Dielectric constant is very high (more 14000) in the vicinity of the peak. Anomalous broad dielectric relaxation have been observed near the temperature of the maximum permittivity, Tm (at 1 kHz). External bias field considerably lowers the value of dielectric losses at low frequencies due to decrease of polar nano regions contribution to the dielectric permittivity.
Impedance spectroscopy studies of SrMnO3, BaMnO3and Ba0.5Sr0.5MnO3ceramics
2014
The impedance spectrum of hexagonal SrMnO3, rhombohedral BaMnO3 and orthorhombic Ba0.5Sr0.5MnO3 ceramics, synthesized by conventional high-temperature method, was studied in a wide temperature and frequency range. The complex impedance plots of Z″ versus Z′ pointed to two contributions originating from grains and grain boundaries. The parameters of electric equivalent circuit were calculated. The semicircles related to the grain boundary are located at the lower frequency side due to higher resistivity and capacity of the grain boundaries. The Ba0.5Sr0.5MnO3 ceramics is characterized by the lowest activation energy related to the grains. The conductivities σac of all the investigated sample…
Broad Distribution of Relaxation Times in 0.6PMN-0.4PZN Relaxor Ceramics
2007
In this paper dielectric spectra of 0.6PMN-0.4PZN ceramic obtained from broadband dielectric spectroscopy is presented. Measurements revealed an unusual relaxor like nature. Two different processes in the dielectric spectra have been observed. High frequency, or short relaxation times, behaviour is typical for ferroelectric crystals. Longest relaxation times do not follow Vogel—Fulcher dependence, which is unusual for relaxors.
Chemical strain effects and changed lattice dynamic in (Sr1-1.5xBix)TiO3ceramics (x ≤ 0.15)
2016
ABSTRACTIn this work lattice strain (induced by chemical Bi substitution on A-site) effects on the lattice dynamic of SrTiO3 ceramics were investigated by broadband dielectric spectroscopy in the very broad frequency range from 10 mHz up to 30 GHz and temperatures from 30 K to 500 K. Obtained results confirmed predicted induce of the ferroelectricity and suppression of the structural phase transition due to substitution of A-site ions – chemical straining of the lattice, both happening at the local scale but evident in macroscopic dielectric spectroscopy measurements. Calculated relaxation time distribution function broadens towards the longest relaxation times with temperature decrease and…
Enhancement of calcium copper titanium oxide photoelectrochemical performance using boron nitride nanosheets
2020
International audience; Photoelectrochemical water splitting under visible light has attracted attention for renewable hydrogen production. Despite prevalent investigations, many challenges still hindered an efficient energy conversion, such as enhancing the reaction efficiency in visible light. Thus controlling the photoelectrode materials is an essential step in designing new materials for water splitting. CaCu3Ti4O12 (CCTO) has received great attention as photocatalyst under solar light due to its combined band gap as result of the presence in its structure of TiO2 active in UV light and CuO active under visible light. In this work, a cubic CCTO with different amount of exfoliated hexago…
Curing of an epoxy resin modified with nanoclay monitored by dielectric spectroscopy and rheological measurements
2006
Dielectric and rheological measurements have been performed in “real-time” to follow curing reaction on blends of a diglycidyl ether of bisphenol-A epoxy resin with 4,4-methylene bis(2,6-diethylaniline) hardener and different amounts of organically modified nanoclay (Nanofil 919) as modifier. The effect of the modifier and its amount on the curing reaction, as well as that of the curing temperature has been studied. Changes in molecular mobility in the reaction mixture have been investigated by dielectric relaxation spectroscopy. Evolutions of ionic conductivity and main relaxation have been analyzed and vitrification times have been obtained and compared with those obtained by rheological …