Papers by Keyword: Ionic Conductivity

Abstract: A conducting solid biodegradable polymer electrolytes based carboxymethyl cellulose (CMC) doped ammonium thiocyanate (NH₄SCN) system with concentration in the range 0 – 25 wt.% of NH₄SCN have been prepared via solution casting method. The impedance study of CMC-NH₄SCN system was measured via Electrical Impedance Spectroscopy (EIS) in the temperature range 303 K – 353 K. The highest ionic conductivity at room temperature (303 K) is 6.48 x 10^-5 Scm^-1 for sample containing 25 wt.% NH₄SCN. The temperature dependence of CMC-NH₄SCN system was found to obey the Arrhenius behaviour where the ionic conductivity increases with increase of temperature. Dielectric data were analyzed using complex permittivity, Ɛ_i for sample with the highest ionic conductivity at various temperatures and found was non Debye behavior. The conduction mechanism of the charge carrier of CMC-NH₄SCN system can be presented by quantum mechanical tunneling (QMT) model.

Abstract: A kind of new plasticizer glycerol carbonate (GC) was synthesized. The poly (acrylonitrile-methyl methacrylate) (P(AN-MMA)) was prepared by bulk polymerization. During the polymerization, glycerol carbonate with 1M lithium perchlorate (LiClO₄) was added to (P(AN-MMA)) to form the gel electrolyte. The effect of the plasticizer on the conductivity of the copolymer electrolyte was studied. The ionic conductivity was found to be 3.3 × 10^-4 S·cm^-1 at room temperature via AC impedance measurement.

Abstract: A Na–ion conducting solid electrolyte system was prepared by using ball milling and sintering method. The electrical conductivity study was carried out as a function of NaI concentration by Electrical Impedance Spectroscopy technique and the maximum conductivity of (1.02±0.19)×10^-4 S cm⁻¹ at room temperature was obtained for the composition 0.50 NaI:0.50 Na₃PO₄. Further characterization was performed by using and Infrared (FTIR) technique. From FTIR spectra, the variation in the peak intensity and shifting is observed due to the presence of P–O and PO₄³⁻ bands that had been shifted indicating changes in polyhedral structure which in turn led to the formation of conducting channel by corner sharing or through edges. The ionic transference number was found in the value of 0.92 which suggests that ions are the charge carriers. The optimum composition with the highest conductivity of the sample considered as a good candidate to be used as solid electrolyte in solid state sodium battery. The sodium battery with configuration: Na/NaI–Na₃PO₄/V₂O₄ was tested by the discharged characteristic at a current of 1.0 μA. The solid state sodium batteries exhibited a discharge capacity of 144mAh/g.

Abstract: Yttria doped ceria display higher ionic conductivity and stabilized phase which possess more advantage for solid oxide fuel cells. By using molecular dynamics simulation, the lattice parameter and oxygen conductivity of Ce_1-xY_xO_2-x/2 (x = 0 - 0.65) at 1273 k have been investigated. Lattice parameters and ionic conductivity both increase with yttria doping while x < 0.15 but over doping of yttria lead to a decreasing trend on them. It is suggested that the closing distance of cation-anion is responsible for this decreasing. The coordination numbers of cations were also analyzed. The results showed that the vacancies prefer to locate near Y ions and vacancy ordering is independent with vacancy content.

Abstract: The aim of this study was to obtain 4.5%mol Y₂O₃-doped ZrO₂ dense with submicrometer grain size and studying the effects of using oxygen flow during calcination in the electrical properties of bodies sintered. The powders were synthesized by the Pechini method. After synthesis, the resins were dried and the calcinations were performed in air and in oxygen flow at 600°C for 2 h. The powders were pressed with 1600 MPa and sintered by Two Step Sintering (TSS) at 1500°C / 5 min and 1200°C, 1300oC, 1400°C, remaining at these temperatures for 2 and 10 hours. The sinterized samples were characterized by X-ray diffraction, apparent density, scanning electron microscopy and impedance spectroscopy. The apparent densities were greater than 94% for all conditions of calcination and sintering. The value of the activation energy was 0.7eV for the grain and 0.9 eV for the grain boundaries.

Abstract: Strontium and magnesium-doped lanthanum gallate is a solid electrolyte with higher ionic conductivity than yttria-stabilized zirconia. This perovskite-type ionic conductor has been investigated for application as solid electrolyte in intermediate-temperature solid oxide fuel cells. In this work the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ composition was synthesized by a soft chemistry route seeking for a more homogeneous microstructure. Densification was carried out by the conventional method and by fast firing. The ionic conductivity of sintered specimens were evaluated by impedance spectroscopy. The apparent density was about 90% and 94% for fast fired and conventionally sintered specimens, respectively. No significant difference was found for the grain conductivity of specimens fast fired at 1500 oC for 5 min and sintered by the conventional method at 1450 oC for 4 h.

Abstract: In this work, the yttrium rich rare earth concentrate (Re₂(CO₃)₃) was used as additive aiming stabilization of cubic an tetragonal phases at commercial zirconium oxide with 3% mol of yttrium oxide. The use of high purity rare earth oxide as additive is being commercially used and this work aims to demonstrate the potential use of lower cost additives to produce solid electrolyte for oxygen sensors and fuel cell applications. The powders for the additive production were synthesized by the controlled precipitation method. After synthesis, the powders were de-agglomerated using mechanical grinding and mixed to commercial zirconia to produce the compositions ZrO₂:3% Mol Y₂O₃:ƞ % Mol Re₂O₃ (ƞ=3,4,5,6), followed by uniaxial press and sintering at 1500 ⁰C in two hours. The obtained sintered densities were above 96% of theoretical. X-Ray diffractometric analysis and Rietweld refinement demonstrated the stabilization of cubic and tetragonal phases for all samples with yttrium rich rare earth concentrate additives. Finally the electric behavior of the evaluated samples was carried out with complex impedance spectroscopy, showing conductivity improvement for samples with the chosen additive. At 500 ⁰C the sample A-9% had a conductivity of 1,11E^-3 Ω^-1.cm^-1, well above of the sample without additive with conductivity 5,88E^-4 Ω¹.cm^-1, indicative that use of yttrium rich rare earth concentrate as additive increases considerably the ionic conductivity of comercial zirconium oxide. Key words: rare earth concentrate, controlled precipitation, ionic conductivity

Abstract: Solid electrolytes based on stabilized zirconia have been studied a long time ago in its cubic phase because of its electrical properties, which make them excellent candidates to be used in applications such as oxygen sensors and solid oxide fuel cells [1], [2]. Lambda sensor or oxygen sensor, as it is also known, is a device that measures the oxygen concentration of the gases that flow through the exhaust pipe. Physically, the lambda sensor has two electrodes. The outer which is exposed to the exhaust gases and the inner to the air (reference) [3]; these electrodes are made, generally, of porous platinum. The ceramic material, i.e., zirconium oxide, is placed in between the electrodes, so the oxygen ions can move from one electrode to another. As one of the electrodes is exposed to the reference gas, the voltage generated is a measure of the concentration of oxygen in the exhaust gases [4].

Abstract: Oxygen ion conductors of zirconia based ceramics are a class of materials with technological applications in several application areas: sensors of chemical species, oxygen pumps, solid oxide fuel cells among others [1]. For these applications, the zirconia must possess the fluorite type crystal structure, or close to it. Such oxides with this structure are the classic oxygen ion conductors [2]. The fluorite structure consists of a cubic lattice of oxygen ions surrounded by cations. The cations are arranged in a face centered cubic structure with anions occupying tetrahedral positions. This leads to an open structure with large empty octahedral interstices.

Abstract: The gadolinia doped ceria was developed in Ce_0,8Gd_0,2O_1,9 composition, with the objective to study the influence of calcination temperature on the ionic conductivity of sintered samples (pellets) used as solid electrolyte for the fuel cells applications. The powder was synthesized by the polymeric precursor method (Pechini) from cerium and gadolinium nitrates hexahydrates, obtaining a polymeric resin characterized by infrared spectroscopy. The heat treatments at 600 and 800°C resulted on oxides formation which have been characterized by infrared spectroscopy and X-ray diffraction for each sample. In each case, the fluorite type structure was identified. The pellets were formed by uniaxial pressure and sintered at 1500°C with relative densities of 93.1 and 89.4% for the samples calcined at 600 and 800°C, respectively. The microstructure evaluation was performed by scanning electron microscopy, and the electrical characterization was carried out by impedance spectroscopy, reaching a conductivity of 1.49x10^-4 S/cm at 400°C in this work.