Dc Ionic Conductivity Research Articles

AC conductivity studies of composite polymeric electrolytes

Ac conductivity studies carried out over a temperature range of 0–100°C for polymeric electrolytes from the PEO-LiClO 4- α-Al 2O 3 system are reported. Electrolytes of various salt concentrations and containing 15 mass% α-Al 2O 3 are studied. The contribution of charge carrier concentration and ion mobility to the dc ionic conductivity of these composite polymeric electrolytes is discussed. A change in the temperature dependence of ionic conductivity is observed around the melting point of the crystalline phase of the composite electrolytes. An increase in dielectric constant following this phase transition is also observed. Above the melting temperature, an increase in the conductivity depends either on an increase in ionic mobility (samples with low salt concentration) or on the creation of charge carriers (samples with high salt concentration).

Significance of intermediate range structure for electrical conduction in alkali germanate glasses

The dc ionic conductivity of the xM 2O:(1 - x)GeO 2 glass series has been measured as a function of temperature and composition where M is K or Rb and 0.0023 ≤ x ≤ 0.60. The structure of the same glasses have been determined by measuring X-ray absorption fine structures, densities and X-ray photoelectron, Raman and infrared absorption spectroscopies. With increasing alkali concentration the activation energy of conductivity decreases followed by an increase and then a more rapid decrease at x ≈ 0.1. By correlating this complex composition dependence of electrical conductivity with the structura information we demonstrate that the intermediate range structure of glass affects ion transport in alkali germanate glasses.

Effects of dynamic spatial disorder on ionic transport properties in polymer electrolytes based on poly(propylene glycol)(4000)

The equivalent ionic dc conductivity (Λ) generally exhibits a dramatic concentration dependence in electrolytic systems based on the host polymer poly(propylene glycol) of molecular weight 4000 (PPG4000). In particular, Λ typically increases rapidly with increasing salt concentration passing through a temperature dependent maximum at high concentration. Prompted by recent reports on a microscopic phase separation occurring in these electrolytes, we here report vibrational spectroscopic, ionic conductivity, and restricted diffusion data for ion-conductors based on PPG4000 complexed with the lithium salts LiCF3SO3 and LiN(CF3SO2)2, in an attempt to resolve seemingly contradictory results concerning ionic transport phenomena in these complexes. We find that the differential salt diffusion coefficient Ds, describing bulk salt motion over long time scales, exhibits a qualitatively similar concentration dependence as Λ. This is contrary to recent F19 pfg-NMR diffusion results for the PPG4000-LiCF3SO3 system which show that the anionic diffusion coefficient decreases monotonically with increasing salt concentration and is inversely proportional to solution shear viscosity. As determined from analyses of characteristic vibrational modes of the [CF3SO3]− and [(CF3SO2)2N]− anions, respectively, the spectroscopic data show very small changes in the distribution of anionic species over the range of electrolyte compositions corresponding to a sharp enhancement of Λ. The results are interpreted in terms of slowly fluctuating salt-rich electrolyte microdomains in equilibrium with salt-depleted polymer regions.

Single-Ion Conduction in UV-Crosslinked Films of Poly(urethane-co-(alkali-metal methacrylates))

A series of crosslinked copolymers of poly(ethylene glycol-co-2,4-tolyl diisocyanate-co-(alkali-metal methacrylates)) were prepared by copolymerization of polyurethane oligomer with alkali-metal methacrylate. Cast films of these copolymers obtained by UV-crosslinked polymerization are completely amorphous and have a relatively low T g . The films provide good mechanical properties and high ionic conductivity without additional solvent or inorganic salts. DC ionic conductivity of the films at room temperature is stable over time indicating that the copolymer is a cationic single-ion conductor. AC conductivity of these films depends mainly on the ionic radius, segmental motion of the polymer chains and local environment of the ions in the polymer matrix.

Attempts at lithium single-ionic conduction by anchoring sulfonate anions as terminating groups of oligo(oxyethylene) side chains in comb-type polyphosphazenes

Novel comb-type polyphosphazenes with anchored lithium sulfopropyl oligo(oxyethylene) side chains [SEP] were synthesized by a one-step reaction with lithium bisulfite and polyphosphazenes containing oligo(oxyethylene) side chains terminated with allyl groups [AEP]. The dc ionic conductivity ([sigma]) of SEP was measured using lithium electrodes and compared with hybrid (polymer-salt complexes) between LiSO[sub 3]CF[sub 3] and the corresponding non-sulfonate comb-type polymer [MEP], i.e., poly(bis[[omega]-methoxyoligo(oxyethylene)]phosphazene). While the time dependence of [sigma]/[sigma][sub o] ([sigma][sub o]: initial conductivity) of SEP showed a constant value, that of the hybrid system drastically decreased with time due to the self-polarization by mobile anions. The stationary values of [sigma] after prolonged electrolysis were 7.1 x 10[sup [minus]8] S cm[sup [minus]1] for SEP and 8.5 x 10[sup [minus]7] S cm[sup [minus]1] for the hybrid at 1.0-V dc supply. 16 refs., 2 figs., 2 tabs.

Ionic conductivity and the mixed alkali effect in a binary system: A Monte Carlo study

The ternary lattice gas comprising vacancies and the two atomic components A and B has been studied with Monte Carlo methods for vacancy contents up to 20%. The order/disorder ternary phase diagram was first determined prior to an investigation of the ionic conductivity of the atomic components. Similar to the findings of Sato and coworkers using the Path Probability Method we found that correlation effects in the dc ionic conductivity are largely responsible for the mixed alkali effect. The correlation effects are somewhat stronger than predicted by Sato and coworkers. The behavior of the ionic conductivities was related to the detailed ordering behavior.

Multiple frequency spin-lattice relaxation time and ionic conductivity measurements of Li 2S + SiS 2 glasses from 1 Hz to 40 MHz

Many measurements have been made of the temperature dependence of the spin-lattice relaxation time T 1 for ionically conducting glasses and the ubiquitous observation is that the activation energy for T 1 ranges from a factor 2–5 lower than the dc ionic conductivity activation energy for the same glass. This has prompted much deserved discussion and yet a definitive solution to the discrepancy has not yet been advanced. In this study, wide frequency range measurements of both T 1 and σ ac have been made on glasses in the highly conducting series Li 2S + SiS 2 to test the hypothesis that the source of the discrepancy lies not in two fundamentally different phenomena being measured by the two different techniques, but rather in the simpler fact that the timescales that they use to measure the same phenomena are vastly different. In NMR, the frequencies used are always above 1 MHz and always correspond to a frequency-dependent regime of T 1, whereas the conductivity is measured as a frequency-independent quantity. These highly conducting glasses provide the rare opportunity to compare activation energies for both NMR and conductivity under conditions of frequency independence and it is found that the two activation energies thus determined agree within experimental error. The source of the discrepancy reported until now is suggested to be due to the fact that the conductivities of glasses have not been high enough to show frequency-independent behavior at the NMR frequencies below T g.

Cationic Conductivity of Blend Complexes Composed of Poly[oligo(oxyethylene) methacrylate] and the Alkali Metal Salts of Poly(sulfoalkyl methacrylate)

Two kinds of alkali metal salts of poly(sulfoalkyl methacrylate)s (PSAMM) were prepared, with which the blend complexes of poly[oligo(oxyethylene) methacrylate] (PMEOn) were formed. These blend complexes contain neither organic plasticizer nor low molecular weight Li-salt and are considered to be single-cationic conductors which are characterized by stable dc ionic conductivity. Cationic conductivity is deeply influenced by the glass transition temperature, cation species, polar group (acrylonitrile), the concentration of polymeric salts, and the size of side-group in PSAMM. An optimum Li+-ionic conductivity of 1.1×10−6 S cm−1 at 25°C is obtained for the blend complex P(0.6MEO18−0.4AN)/P(0.5SHMLi−0.5AN) (AN, acrylonitrile; SHMLi, lithium sulfohexyl methacrylate) with O/Li=72.

Enhancement of dc ionic conductivity in dispersed solid electrolyte system - Sr(NO 3) 2:γ-Al 2O 3

dc ionic conductivity in dispersed solid electrolyte system (DSES) - Sr (NO 3) 2:γ-Al 2O 3 was studied from 100°C to about 570°C. Considerable enhancement was noticed in the conductivity in the extrinsic region. The enhancement was found to be maximum for 29.3 m o of γ-alumina. X-ray studies ruled out any formation of a solid solution between the host matrix and the dispersoid even at the melting point of the host matrix.

Two-point dc ionic conductivity measurements in the superionic phase of Cu 2−xSe

dc ionic conductivity (σ i) of the mixed superionic conductor Cu 2− x Se, with 0.01 ≤ x ≤ 0.26, is measured in the temperature range from 160 to 250 °C. The new two-point measuring method is presented; the experimental set-up is simplified and very small samples can be treated, which strongly increases the speed of the measurements. The temperature dependence of σ i is found to be Arrhenius, with only weakly concentration-dependent activation energy A = 125 ± 5 meV. For compositions x ≳ 0.1, the concentration dependence of σ i is linear, σ i ∝ (1−1.3 x). As x is decreased from 0.1 to zero, σ i is nonlinearly enhanced, which confirms the importance of ionic correlations in the mechanism of superionic conduction.

Study of dc ionic conductivity in single crystals of RbNO 3

dc ionic conductivity has been studied on single crystals of RbNO 3 grown by slow evaporation method. The range of temperature covered is from room temperature to its melting point atmospheric pressure. An attempt is made to correlate the known phase transitions with the variation of ionic conductivity with temperature.

Preparation and electrical properties of oxygen ion conductors in the Bi2O3−Y2O3 (Er2O3) systems

Dense bodies (98% of theoretical density Dth) in the compositional range 12–30 mol% Y2O3 and 18–20 mol% Er2O3 of the Bi2O3−Y2O3 (Er2O3) systems were prepared by coprecipitating oxalates. Sintering process, grain growth and microstructural development were also studied. It was found that a very rapid grain growth took place in these ceramics which impeded the migration of the residual porosity located at the interior of the grains. dc ionic conductivity and ac impedance plane measurements on sintered samples were carried out. Erbia-containing samples exhibit the larger ionic conductivity domain, from 1 to 10−23 Pa of oxygen partial pressure and electrode-electrolyte reduction reaction of Bi2O3 took place. The impedance analysis on low yttria-containing samples (12 mol% Y2O3) shows a very high electrical conductivity. In all cases only one semicircle at low temperature was found which was attributed to the bulk conductivity contribution. Only in erbia-containing samples does a grain boundary contribution seem to be detected. Finally, a Warburg diffusion contribution could explain the quarter semicircle of low-frequency arc at the high- and intermediate-temperature regions.

Cluster polarization inSr1−xCexF2+x: Hopping transport in fractal structures

In this paper we present results obtained with ionic thermocurrent and ac-impedance measurements performed on single crystals of ${\mathrm{Sr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ (0.0001<x<0.4). Attention has been focused on the dielectric polarization observed in these crystals occurring just before the onset of dc ionic conductivity. In addition, the activation energy (E) for the dc ionic conductivity has been determined. Both the polarization and ionic conductivity are caused by hopping of interstitial ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ions. For x=0.05, a maximum in the dielectric constant is observed; at this same concentration, E decreases rapidly. These results have been explained by considering the regions in the crystal near ${\mathrm{Ce}}^{3+}$ impurities as a well-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$-conducting phase which is dispersed randomly in the poorly-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$-conducting ${\mathrm{SrF}}_{2}$ host lattice. Computer simulations have revealed a percolation threshold of the well-conducting phase in the poorly conducting host crystal at Ce concentrations near 3 mol %.

DC and AC ionic conductivity in quartz: A new high temperature mechanism and a general assessment

DC and AC (10 2–10 5 Hz) conductivity measurements both parallel and perpendicular to the z-axis have been performed on synthetic quartz (Sawyer PQ) extending the temperature range up to 950° C. In the lower temperature range (250 < T < 500° C) as-received samples show an activation energy for the process of AC conduction in the z-direction, E = 1.32 eV while at higher temperatures (500 < T < 950° C), a lower energy is found, E = 0.67 eV. Experimental results concerning electrodiffused samples (either “vacuum swept out” and “Na swept in”) have also been considered. The interpretation proposed for the ionic conduction mechanism is consistent both with AC and DC data, considers a wide T range, and allows a comprehensive view of the ionic transport in quartz.

Ionic conductivity in doped fused silica

DC ionic conductivity was measured over 300–800 C in specimens of type-I fused silica doped with various levels of Al2O3/M2O ratio (M = alkali) using blocking and non-blocking electrodes. Although the values of the conductivity depended upon the measurement technique, all the data showed an Arrhenius behavior with the values of activation energies ranging from 35 kcal/mole to 20 kcal/mole for various alkali ions below 500 °C. A slight decrease in activation energy was seen in most of the samples at temperatures greater than 500 °C. When the resistivity at a particular temperature was plotted as a function of Al2O3/M2O ratio, a broad minimum in resistivity was seen between the ratios of 4–12. These results are discussed in terms of the AlO4− and nonbridging oxygen sites in the fused silica structure.

High oxygen ion conduction in some Bi 2O 3-Y 2O 3 (Er 2O 3) solid solutions

Highly densified bodies (~ 98 % theoretical density) of the Bi 2O 3-Y 2O 3(Er 2O 3) systems containing 30 moles % Y 2O 3 and 20 moles % Er 2O 3 respectively were prepared from both mixed oxides and coprecipitated oxalates. DC ionic conductivity and impedance complex plane analysis on sintered samples were performed. Under oxygen partial pressure ranging from 1 to 10 Pa was found that, samples containing 30 moles % yttria showed a pure ionic conductivity up to an oxygen partial pressure of 10 −20 Pa. Samples containing 20 moles % erbia, extended its ionic conductivity up to an oxygen partial pressure of 10 −22 Pa. The impedance analysis shows the presence of only one semicircle at low tempertures and it is attributed to bulk conductivity contribution. The conductivity was higher for the Bi 2O 3-Er 2O 3 sintered solid electrolytes, in such a case, a conductivity as high as 1.38 ohm cm at 700ºC was obtained. The activation enthalpy for the conduction process was calculated in the temperature range from 200º to 700ºC in all the cases. Microstructural development in the sintered sample was also studied.

A Dielectric Study of the State of Water in Plant Stems

Pissis, P., Anagnostopoulou-Konsta, A. and Apekis, L. 1987. A dielectric study of the state of water in plant stems.—J. exp. Bot. 38: 1528-1540. We report on thermally stimulated depolarization current (TSDC) measurements on plant stems of six different species in the temperature range of 77-300 K and over a wide range of water contents, in an attempt to determine the binding modes of water molecules. The measurements revealed the existence of three dielectric dispersions. The first dispersion at low temperatures is attributed to the reorientation of loosely bound water molecules. The origin of the second dispersion at intermediate temperatures is not yet clear. It is either due to the reorientation of tightly bound water molecules or to the relaxation of some botanical materials rather than water. Finally, the third dispersion, at high temperatures, is attributed to water-assisted space charge polarization connected with dc ionic conductivity. The amount of tightly bound water is estimated to be about 0-2 g g~1 of dry material or about 30% of the total water content, the rest being mainly loosely bound water. Little or none of the water behaves dielectrically like pure water. Key words—Free and bound water, dielectric properties, water content. Correspondence to: National Technical University of Athens, Physics Department, Zografou Campus, 15773 Athens, Greece.

ChemInform Abstract: Grain‐Boundary Effect in Ceria Doped with Trivalent Cations. Part 1. Electrical Measurements. Part 2. Microstructure and Microanalysis.

AbstractTheinfluences of porosity, of sintering time, and dopant size and ‐concentration (dopants: Y", Gd", La") on the "grain‐boundary" effect in doped ceria, which leads to a reduced dc ionic conductivity, have been investigated.

Grain‐Boundary Effect in Ceria Doped with Trivalent Cations: I, Electrical Measurements

The “grain‐boundary effect,” which leads to a greatly reduced dc ionic conductivity due to the presence of a blocking layer in the vicinity of the grain boundaries, is studied in detail for ceria ceramics doped with various trivalent dopants (particularly Y3+, Gd3+, and La3+). The effects of porosity, of sintering time, and of dopant size and dopant concentration are investigated. Finally, it is shown that the grain‐boundary effect virtually disappears when nearly silicon‐free starting materials are used.

Temperature dependence of the dc ionic conductivity of beta -AgI and AgCrS2.

Temperature dependence of the dc ionic conductivity of beta -AgI and AgCrS2.