Concentration Dependence Of Conductivity Research Articles

Concentration Dependence of the Activation Energy of Conductivity in Aqueous Sodium Selenite and Potassium Tellurite

The temperature and concentration dependences of conductivity have been studied for aqueous solutions of sodium selenite and potassium tellurite. The corresponding empirical equations have been derived. The activation energies of conductivity in both electrolytes are calculated for different solution concentrations. The ascertained dependence is interpreted in the light of Samoilov's theory on positive and negative hydration of ions. Analysis of the results suggests that the larger the positive hydration of ions, the higher the activation energies of conductivity for the salts.

Electrical properties of heavily doped fluorite-structured BaF2:RF3 (R=La, Pr, Nd, Gd, Tb, Y, Sc) single crystals

The superionic conductivity and dielectric response of heavily doped fluorite-structured Ba1−xRxF2+x (R=La, Pr, Nd, Gd, Tb, Y, Sc; x=0.005–0.45) crystals are reported. The highest ionic conductivity is found for R=Sc and x=0.1. Upon ScF3 doping, small Sc3+ ions rearrange their surroundings, create excessive fluoride interstitial ions and bring about a high ionic conductivity. For each dopant, the concentration dependence of the ionic conductivity is non-linear. A monotonous concentration dependence of the ionic conductivity is found only for La3+ doping. Upon doping with Nd3+, Gd3+, Tb3+, Y3+ and Sc3+ ions, a conductivity maximum is observed at x=0.1–0.2. Upon Pr3+ doping, this maximum is split. The influence of defect clustering on the concentration dependence of the conductivity is discussed.

Electrical conductivity of model composites of an ionic conductor (CuBr) and an insulator (TiO2, Al2O3): experiments and percolation-type model

We present conductivity measurements on composites of a Cu+ ion conductor (CuBr) and a dispersed insulating oxide (titania, alumina). A numerical model, assuming a simple topology and an increased conductivity in narrow regions near the heterophase boundaries, provides a satisfactory description of the experimental results, especially concerning the concentration dependence of conductivity. A bell-shaped curve with concave initial characteristic is obtained for incomplete wetting (CuBr–titania), whereas for strong wetting (CuBr–alumina) a linear relation between conductivity and volume fraction is observed in a certain range.

The relation between high-temperature thermopower, conductivity and oxygen content in YBa 2Cu 3O 6+ x

Experimental data, more detailed and complete than previously available, for thermopower and conductivity in YBa 2Cu 3O 6+ x was obtained in the temperature range 600 to 850°C and oxygen content varying in the limits 0.1≤ x≤0.8 under equilibrium pressure of oxygen. The concentration dependencies of conductivity and thermopower were derived using an equilibrium P(O 2)–T–x diagram. Isothermal plots of thermopower versus the logarithm of conductivity show unusual features in the extrinsic hole regime, i.e. a small inward curvature, an anomalously small slope and a weak temperature dependence were observed. The decrease in the oxygen content at high temperature results in the expected transition to intrinsic behavior and the contribution of electrons to the conductivity. The results obtained have been interpreted in the framework of the band structure comprised of two narrow bands on the background of two broad bands. The main influence of the broad bands is on the position of the chemical potential, whereas the location of the narrow bands relative to the chemical potential of the electrons impacts the electron transport.

A generalised phenomenological dynamic order–disorder model for polymer electrolytes

Abstract We are proposing in this work, apparently for the first time, a generalised model for explaining, directly from the concentration dependence of conductivity, different degrees of dynamic order–disorder transitions in polymer electrolytes.

Computation of Electrical Conductivity of Multicomponent Aqueous Systems in Wide Concentration and Temperature Ranges

A comprehensive model for calculating the electrical conductivity of multicomponent aqueous systems has been developed. In the infinite-dilution limit, the temperature dependence of ionic conductivities is calculated on the basis of the concept of structure-breaking and structure-making ions. At finite concentrations, the concentration dependence of conductivity is calculated from the dielectric continuum-based mean-spherical-approximation (MSA) theory for the unrestricted primitive model. The MSA theory has been extended to concentrated solutions by using effective ionic radii. A mixing rule has been developed to predict the conductivity of multicomponent systems from those of constituent binary cation−anion subsystems. The effects of complexation are taken into account through a comprehensive speciation model coupled with a technique for predicting the limiting conductivities of complex species from those of simple ions. The model reproduces the conductivity of aqueous systems ranging from dilute to concentrated solutions (up to 30 mol/kg) at temperatures up to 573 K with an accuracy that is sufficient for modeling industrially important systems. In particular, the conductivity of multicomponent systems can be accurately predicted using data for single-solute systems.

Temperature and concentration dependent conductivity of potassium doped C 60 films in relation to the phase diagram

Conductivity measurements on potassium doped thin films of C 60 following various preparation procedures are reported. In the resistivity as function of x we report a sharp local maximum at x = 4 and a local minimum near x = 5 in addition to that commonly found near x = 3. These effects are only seen in films prepared with “backdoping”. For the x = 1 films we find a non-metallic quenched mestastable phase below 150°C that can be annealed at 125°C to a stable phase. The relevance of preparation methods and thermal history of the films for the existence of different phases is discussed.

Conductivity mechanism in Li 2SO 4−Ag 2SO 4 binary system

The conductivity data of Li 2SO 4-Ag 2SO 4 represented as M 2SO 4/M' 2SO 4 type solid electrolyte using complex impedance spectroscopy has been analysed in detail. The occurrence of two overlapping semicircles in the complex impedance plane has been discussed extensively in the light of two relaxation times corresponding to Li + and Ag + mobilities. The concentration dependence of conductivity is explained on the basis of surface percolation model.

Potassium channel of cardiac sarcoplasmic reticulum is a multi-ion channel

We have characterized mechanisms of ionic permeation in the K channel of canine cardiac sarcoplasmic reticulum (SR K channel). Ionic selectivity, as measured by relative permeabilities, followed Eisenman sequence l, a low field strength sequence. Slope conductance measured in symmetrical solutions across the bilayer followed Eisenman sequence V. In all cases, the selectivity characteristics of the prominent subconductance state (O1) were similar to those of the main-state (O2). Further, our studies have revealed that this channel differs in three significant ways from the highly characterized SR K channel of skeletal muscle. First, the ratio of permeabilities Cs+ to K+ was a complex function of ion concentration. Second, the concentration dependence of conductance was not well described by the Michaelis-Menten formalism. Instead, we modeled the observed relations using a more general approach based on classical rate theory. Third, mole fraction experiments (Cs+ with K+) demonstrated a prominent anomalous effect. Certain of our Cs+ data required the Eyring rate theory approach for adequate interpretation. We adopted a symmetrical energy profile incorporating ion-ion interaction and thereby accounted for much of the data. We conclude that the canine cardiac SR K channel is significantly different from that of skeletal muscle, and it may accommodate more than one ion at a time.

Electrical Conductivities of Liquid Mn and Mn–Te Alloys

The electrical conductivities of liquid Mn and Mn x Te 100- x alloys were measured by using a high purity alumina cell in the temperature range up to about 1400°C. Their concentration dependence of conductivities exhibited a sharp minimum at the stoichiometric composition MnTe. It suggests that liquid MnTe has the ionic configuration of Mn 2+ and Te 2- at the composition MnTe. The conductivity of liquid MnTe was about 20.7 ohm -1 ·cm -1 at the melting point and the temperature dependence of conductivity was found to be exponential with an energy gap of 1.84 eV. For liquid Mn, the resistivity ρ was 199.5 µΩ·cm at the melting point and its temperature dependence dρ/d T was about 0.022 µΩ·cm/K near the melting point.

Ionic channels with conformational substates

Recent studies of protein dynamics suggest that ionic channels can assume many conformational substates. Long-lived substates have been directly observed in single-channel current records. In many cases, however, the lifetimes of conformational states will be far below the theoretical limit of time resolution of single-channel experiments. The existence of such hidden substates may strongly influence the observable (time-averaged) properties of a channel, such as the concentration dependence of conductance. A channel exhibiting fast, voltage-dependent transitions between different conductance states may behave as an intrinsic rectifier. In the presence of more than one permeable ion species, coupling between ionic fluxes may occur, even when the channel has only a single ion-binding site. In special situations the rate of ion translocation becomes limited by the rate of conformational transitions, meaning that the channel approaches the kinetic behavior of a carrier. As a result of the strong coulombic interaction between an ion in a binding site and polar groups of the protein, rate constants of conformational transitions may depend on the occupancy of the binding site. Under this condition a nonequilibrium distribution of conformational states is created when ions are driven through the channel by an external force. This may lead to an apparent violation of microscopic reversibility, i.e., to a situation in which the frequency of transitions from state A to state B is no longer equal to the transition frequency from state B to state A.

Electronic Properties of Liquid Cu–Te, Ag–Te, Au–Te and Pd–Te Binary Alloys

Liquid Ag–Te and Cu–Te systems exhibited sharp minima in the conductivity and the susceptibility at the stoichiometric composition M 2 Te. Furthermore, liquid Cu–Te system exhibited a weak maximum in the conductivity near 15 at%Cu concentration. For liquid Au–Te system, the concentration dependence of conductivity increases gradually with increasing Au concentration and that of susceptibility has a smooth variation with Au concentration. For liquid Pd–Te system, that of conductivity exhibited a rapid increase from Te-side to Pd-side. On the basis of the Mott model, the density of states at the Fermi level E F is estimated from these experimental results of the conductivity and susceptibility. The difference in their concentration dependence among four liquid systems is characterized by the amount of the sp-d hybridization and the position of the energy level of d-state E d relative to E F .

Phase diagram and conductivity of the polymer electrolyte: PEORLiCF3SO3

A simple model for the concentration dependence of the electrical conductivity of the polymer electrolyte: poly(ethyleneoxide) — LiCF3SO3 is presented. It is assumed that the crystals with stoichiometry: 4 polymer oxygens to 1 lithiumion are insulating and the surrounding conducting solution is saturated in the 4∶1 crystals. Correcting the space available for conduction with a volume correction factor accounts qualitatively for the concentration dependence of the conductivity.

Ionic association and the Fuoss–Onsager conductance equation: aqueous KI

Results are reported for a reevaluation of the data for aqueous KI solutions using a modified application of the 1957 Fuoss–Onsager conductance equation in which it is reduced to a one-parameter equation with KA as the unknown. A single value of å is sufficient to account for the concentration dependence of conductance over the temperature range, 5–55 °C, and a small, but nevertheless finite, degree of ionic association is thus predicted for KI in aqueous solutions.

The conductivity of a cation‐exchange resin

AbstractAn equation relating the equivalent conductance of ions in a cation‐exchange resin to their conductance in water and the volume fraction of polymer in the swollen resin has been tested using data for the conductance of potassium ions in crosslinked polymethacrylic acid. The equation is successful for degrees of ionization at which counterion binding is not large and for degrees of swelling sufficiently high for the network to exert no sieve action on the ions. The concentration dependence of conductivity in the resin is determined by a relaxation effect similar to that in free solution and an electrophoretic which has been treated using the Kozeny law for fluid flow in a porous medium. These effects tend to cancel one another so that the concentration dependence is small. When the mean pore diameter of the network approaches the diameter of the counterions the observed conductivity is less than the theoretical value.