Search results for "ionic conductivity"
showing 10 items of 56 documents
Ion diffusion-controlled thermally stimulated processes in x-ray irradiated halide crystals
2003
The ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF2, BaF2, LiBaF3 and KBr crystals were investigated above 290 K by means of the ionic conductivity, ionic thermally stimulated depolarisation current (TSDC) and thermal bleaching techniques. Under a DC field the halide crystals store large ionic space charge. We were able to detect in CaF2, BaF2, LiBaF3 and KBr in the extrinsic ionic conductivity region a series of the ionic defect (the interstitial anion and/or anion vacancies - in fluorides; the cation vacancies - in KBr) release stages: 3-6 wide and overlapping ionic TSDC peaks. The correlated data of the ionic TSDC and the F band thermal show tha…
Structural and electrochemical investigation on re-cast Nafion membranes for polymer electrolyte fuel cells (PEFCs) application
2006
Abstract Starting from a 5 wt% ion power Nafion® solution and dissolving the dry residue in a suitable solvent (10 wt% solution in dimethylacetammide), re-cast Nafion films were developed for polymer electrolyte fuel cells (PEFCs) application. The used Doctor-Blade casting technique allowed to prepare scaled-up membranes comparable to the commercial Nafion ones with good mechanical resistance, thickness homogeneity and an excellent reproducibility. The differences between the re-cast membrane nanostructure and that of the commercial Nafion were investigated by synchrotron small-angle X-ray scattering. The obtained re-cast membrane shows at ambient conditions a semi-crystalline structure wit…
Dielectric characterization and ionic conductivity of α-LiIO3 crystals related to the growth conditions
2000
Abstract The dielectric response of α-LiIO3 has been studied at room temperature between 20 Hz and 1 MHz with various types of electrodes and compared to the results in the literature. By changing the sample thickness, a relaxation of space charges is clearly identified and the bulk ionic conductivity is deduced from the admittance diagram. Finally a comparison is carried out between chromium doped and undoped crystals obtained from acid and neutral growth solutions.
Electrical conductivity and micro-Raman scattering studies of ionic conduction in Li1−xHxIO3 solid solutions
2002
Abstract Li 1− x H x IO 3 solid solutions have been investigated by ac electrical conductivity and micro-Raman techniques, for x ≤0.32. The presence of protons leads to a continuous reduction of the anisotropic intrinsic conduction of the system. The in-plane conduction mechanism would be by Li + vacancy hopping, while a mixed process by interstitial Li + and H + would account for the conduction along the c -axis. The solid solutions undergo the same phase transition sequence as the pure crystal, but the presence of the protons shifts the transition temperatures to lower values. Micro-Raman spectroscopy has been successfully introduced to demonstrate that proton mobility occurs preferential…
Thermoelectric Transport in Cu7PSe6 with High Copper Ionic Mobility
2014
Building on the good thermoelectric performances of binary superionic compounds like Cu2Se, Ag2Se and Cu2S, a better and more detailed understanding of phonon-liquid electron-crystal (PLEC) thermoelectric materials is desirable. In this work we present the thermoelectric transport properties of the compound Cu7PSe6 as the first representative of the class of argyrodite-type ion conducting thermoelectrics. With a huge variety of possible compositions and high ionic conductivity even at room temperature, the argyrodites represent a very good model system to study structure-property relationships for PLEC thermoelectric materials. We particularly highlight the extraordinary low thermal conduct…
Converting external potential fluctuations into nonzero time-average electric currents using a single nanopore
2015
The possibility of taking advantage of a fluctuating environment for energy and information transduction is a significant challenge in biological and artificial nanostructures. We demonstrate here directional electrical transduction from fluctuating external signals using a single nanopore of conical shape immersed in an ionic aqueous solution. To this end, we characterize experimentally the average output currents obtained by the electrical rectification of zero time-average input potentials. The transformation of external potential fluctuations into nonzero time-average responses using a single nanopore in liquid state is of fundamental significance for biology and nanophysics. This energ…
Relaxation and charge transport in mixtures of zwitterionic polymers and inorganic salts
2009
Dielectric spectroscopy is employed to analyze the molecular dynamics and the charge transport in mixtures of zwitterionic polymers of the type poly(3-[N-(omega-methacryloyloxyalkyl)-N, N-dimethylammonio]propanesulfonate) with sodium iodide in the frequency range of 10(2) Hz-10(7) Hz and in the temperature range of 110 K-400 K. The amount of inorganic salt added varies from 0-200 mol-% relative to the number of zwitterionic groups present in the polymer, contributing strongly to the conductivity. One relaxation process is observed whose relaxation rate depends strongly on the length of the aliphatic spacer between the polymethacrylate main chain and the zwitterionic group. Exhibiting an Arr…
Ion diffusion-controlled processes in fluoride crystals
2001
Ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF 2 , BaF 2 and LiBaF 3 crystals (X-ray irradiated at 290 K) have been investigated by means of ionic conductivity and the correlated ionic thermally stimulated depolarisation current (TSDC), and radiation-induced optical absorption band thermal bleaching techniques at 290-650 K. It was found that under a DC field fluorides store large ionic space-charge. In CaF 2 , BaF 2 and LiBaF 3 , by using the ionic TSDC technique we were able to detect a series of the interstitial anion and/or anion vacancy delocalisation stages in the extrinsic ionic conductivity region. At least 4-6 wide and overlapping ionic TSD…
New synthetic strategies for the enhancement of the ionic conductivity in Ce0.8Sm0.2O2-x
2013
Introduction Samarium-doped ceria has been widely investigat-ed for electrochemistry applications as full density elec-trolyte for intermediate temperature solid oxide fuel cells (IT-SOFC), between 500°C and 800°C [1]. One of the main challenges for the ceria-based electrolytes is to decrease the resistivity at the grain boundary zone, especially in this low temperature range. Microstructure and morphology of the powder play a fundamental role on the densification behaviour and grain boundary properties, thus affecting the overall conductivity of electrolytes [2]. In this light, solution combustion syn-thesis (SCS) represents a flexible method to produce ultra fine powders with suitable mic…
Low-Frequency Relaxation Phenomena in α-LiIO3: The Nature and Role of Defects
2002
The lithium iodate ionic conduction in the polar c-axis direction is studied between 35 and 470 K for crystals grown in various conditions. So far, to separate processes induced by the nature of electrodes, the impedance spectroscopy technique had been used at room temperature with both metallic and ideally polarizable insulating electrodes, so that a relaxation of space charges was clearly identified. Here, the temperature dependence of the hopping ionic conductivity exhibits quite different activation energies well related to the growth conditions. Following low-temperature Raman and thermodynamic experiments, a new approach based on a vacancy diffusion mechanism is proposed. Experimental…