Papers by Keyword: Ionic Conductivity

Abstract: MAlSi₃O₈ (M = Li, Na, K) was synthesized by solid-phase reaction at 1000 °C using M₂CO₃ (M = Li, Na, K), Al₂O₃, and SiO₂ as the starting materials, and its ionic conduction was studied in the temperature range 475–800 K. It was confirmed from powder X-ray diffraction profiles that the crystalline phases of the prepared MAlSi₃O₈ were the same as those of orthoclase. Moreover, the ionic conductivity of NaAlSi₃O₈ was about 10 times higher than that of LiAlSi₃O₈ and KAlSi₃O₈. The activation energies for ionic conduction were estimated to be in the range of 0.70–0.77 eV, with NaAlSi₃O₈ exhibiting the lowest activation energy. The result suggests that the magnitude of the activation energy cannot be determined only from the ionic radius.

Abstract: In this paper some recent progress in the area of Monte Carlo simulation of diffusion via the interstitialcy mechanism in a randomly ordered binary alloy is reviewed. Topics discussed include the calculation of tracer correlation factors fA and fB as a function of composition and jump frequency ratio wA/wB and interstitialcy correlation factors fI; which play a crucial role in the interpretation of ion-conductivity data. The percolation behavior of fI when wA ≪ wB is analysed in detail and limits of the tracer diffusivity ratios bD A/bD B for alloy compositions below the percolation threshold are presented. Allowance for non-collinear jumps (partly) replacing concurrent collinear site exchanges leads to a reduction of diffusion correlation effects. This goes along with a shift of the diffusion percolation threshold to lower concentrations of the (more) mobile component B. Even stronger changes of mass and charge transport compared to an exclusively collinear interstitialcy scheme are observed for additional contributions of direct interstitial jumps. It is remarkable that for both extensions of interstitialcy-mediated diffusion the Haven ratio appears to be greater than unity in certain composition ranges poor in B.

Abstract: A single phase perovskite, Y_xSr_1−xTi_0.6Fe_0.4O_3-δ (x= 0.06-0.09), was fabricated at 1350°C in air by sol-gel method. The effects of Y-and Fe-doping into SrTiO₃ on phase structure, electrical conductivity, ionic conductivity and its impedance behavior were investigated. The optimized Y_0.07Sr_0.93Fe_0.4Ti_0.6O_3-δ sample exhibits an electrical conductivity of 0.135 S·cm^-1 at 800 °C. Y-doping decreases the migration energy for oxygen ions, leading to a significant increase in ionic conductivity. The ionic conductivity of Y_0.09Sr_0.91Ti_0.6Fe_0.4O_3-δ sample varies from 0.0052 S· cm^-1 at 600°C to 0.02 S·cm^-1 at 800°C. Impedance characteristics over a wide frequency range of 0.01Hz-100 KHz reveal that the resistance of ionic conduction is predominantly influenced by grain boundary, the relaxation time of which decreases with increase of Y-doping amount.

Abstract: The chlorine-doped complex oxide Ba₂CaNbO_5.475Cl_0.05 based on barium calcium niobate was synthesized using the solid state method. It was found that the introduction of chloride ions leads to the increase of the cell volume. Structure and electrical properties have been investigated. Electrical conductivities were measured by varying the temperature in dry (pH₂O=3.5·10^-5 atm) and wet (pH₂O=2·10^-2 atm) air. The composition Ba₂CaNbO_5.475Cl_0.05 is capable to dissociative dissolution of water vapor and can exhibit proton transport. Chlorine doping increases the conductivity of matrix compound Ba₂CaNbO_5.5, the difference between un-and chlorine-doped samples is up to one order of magnitude at low temperatures.

Abstract: Corn starch (CS) – sodium chloride (NaCl) based polymer electrolytes were prepared by solution casting technique. At room temperature, CS-NaCl film with ratio of 70 wt. % - 30 wt. % demonstrates the highest ionic conductivity in the range of (1.72 ± 0.12) x10^-5 Scm^-1. Temperature-dependence ionic conductivity study follows Arrhenius model and using related plot, the activation energy for highest conducting composition is 0.16eV. The transport number measurement studies confirmed that the ionic conductivity of this polymer electrolyte is due to ions. Fourier transform infrared spectroscopy (FTIR) analysis proved the interaction between CS and NaCl.

Abstract: The polymer blend electrolytes composed of poly (ethyl methacrylate)(PEMA) and Poly (vinyl acetate)(PVAc) as host polymer and lithium perchlorate (LiClO₄) as a salt are synthesized by solvent casting technique. The polymer membranes with different wt% of PEMA and PVAc are subjected to AC impedance analysis for the investigation of ionic conductivity. The maximum ionic conductivity of 3.541 X 10^{- 5}Scm^{- 1} at 303K is reported for PEMA/PVA_C (70/30wt%) –LiClO₄ (8wt%) polymer blend electrolyte system.The complexation has been confirmed by XRD and FTIR techniques. The glass transition temperature (T_g) of the blend polymer electrolytes has been obtained from DSC measurements. The SEM micrographs show the surface morphology of the prepared samples. The electrochemical stability of the sample exhibiting high conductivity has been carried out using linear sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements. The potential window has been found to be-2.5 to +2.5 V. The lithium transference number evaluated using chronoamperometry technique results in a value of 0.90. The dielectric behavior of the solid polymer blend electrolytes has been analyzed as a function of frequency and temperature. The dc conductivity values obtained from the conductance spectra match the ac impedance results. The photoluminescence spectra that contain information about the local free volume of the prepared samples justify the conductivity results. The two and three dimensional images of the maximum ionic conducting sample exhibit numerous micropores.

Abstract: The purpose of this study is to improve the kinetics of styrene monomer accumulation in polyvinylidene fluoride films with radiation-chemical grafting of styrene monomer. The work has proved that the degree of grafting depends on the absorbed dose of helium ions, temperature and composition of the grafting solution.

Abstract: Effect of Cobalt doped 8YSZ on the ionic conductivity. SOFCs mostly operate at higher temperature. By substitute with dopants, it can reduce the operating temperature and costs. In this experiment, cobalt (1, 2 and 3 mol%) mixed with 8YSZ and sintered at 1550 °C, hold for two hours. Crystal structure, microstructure, sintering behaviour and ionic conductivity at 300 °C were investigated. XRD demonstrates three phases (cubic, monoclinic and tetragonal) were obtained. It was confirmed that small additions of Co-doping promotes densification, grain growth and ionic conductivity compared to pure 8YSZ. YSZZn obtained the highest ionic conductivity1.36 x 10^-5 Ω^{− 1} cm^-1 at 300 °C.

Abstract: Pure 8 mol% yttria stabilized zirconia (YSZ) and 3mol % of Fe-doped YSZ electrolyte from different source of Fe (p)in oxide form (pure iron oxide powders, Fe₂O₃) and Fe(s) source from salt (iron nitrate, Fe(NO₃)₃) were prepared and sintered at 1550°C for 2 hours. The effect of Fe dopant from different source of Fe to the crystal structure and ionic conductivity of 8YSZ samples were investigated. The addition of 3 mol % Fe from iron nitrate source (sample 3Fe(s)YSZ) greatly enhanced the growth of monoclinic phase as compared to 8YSZ sintered samples while the addition of 3 mol % Fe from pure iron oxide powder source (sample 3Fe(s)YSZ) enhanced the crystallization of cubic phase and decrease the monoclinic phase. The addition of Fe significantly enhanced the ionic conductivity of 8YSZ sample for both source of Fe. However, 3Fe(p)8YSZ has smaller grain resistivity and thus has higher conductivity compared to 3Fe(s)YSZ.

Abstract: The electrospun poly(vinylidene fluoride-co-hexafluoropropylene)/montmorillonite nanofibrous composite membranes (esCPMs) were prepared by electrospinning technique using a mixture of different amounts of montmorillonite (0, 3, 5, 7 and 10 wt%) into 16 wt% of PVDF-HFP polymer solution in 7:3 wt% of acetone and dimethylacetamide as the solvent. The effect of montmorillonite (MMT) on electrospun PVdF-HFP membrane has been studied by XRD, DSC, TGA and tensile strength analysis. It is found that electrospun PVDF-HFP/MMT nanofibrous composite membrane obtained using 5wt% MMT has a higher porosity, electrolyte uptake, ionic conductivity, electrochemical stability window and showed higher specific capacitance and good compatibility with electrode materials.