Ion Migration Process Research Articles

Atomic Level Investigations of Lithium Ion Battery Cathode Materials

The defect energetics, ion migration processes and surface structures of lithium ion battery cathode materials LiCoO 2 and Li M PO 4 ( M = Mn, Fe, Co, or Ni), probed using a Born model description of atomic interactions, are reported. The lowest energy intrinsic disorder types comprise lithium deficiency in the case of LiCoO 2 and cation antisite defects in the case of the orthophosphates. Lithium diffusion in LiCoO 2 is confirmed to be two dimensional, with a calculated activation barrier of 0.45 eV, whereas in Li M PO 4 compounds diffusion is one dimensional only, with a barrier decreasing from 0.62 to 0.44 eV across the transition metal series. Unlike the linear path calculated for LiCoO 2 , in orthophosphates the Li ion follows a curved path between vacancies. Examination of low index surfaces in LiCoO 2 and LiFePO 4 further illustrates the utility of these methods for probing materials systems on the atomic level.

Defect model for the mixed mobile ion effect revisited: An importance of deformation rates

The progress in understanding the behavior of glassy mixed ionic conductors within the concept of the defect model for the mixed mobile ion effect [V. Belostotsky, J. Non-Cryst. Solids 353 (2007) 1078] is reported. It is shown that in a mixed ionic conductor (e.g., mixed alkali glass) containing two or more types of dissimilar mobile ions of unequal size sufficient local strain arising from the size mismatch of a mobile ion entering a foreign site cannot be, in principle, absorbed by the surrounding network-forming matrix without its damage. Primary site rearrangement occurs immediately, on the time scale close to that of the ion migration process, through the formation of intrinsic defects in the nearest glass network. Neither anelastic relaxation below glass transition temperature, T g, nor viscoelastic or viscous behavior at or above T g can be expected being observed in this case because the character of the stress relaxation in a wide temperature range is dictated above all by the deformation rates employed locally to the adjacent network-forming matrix. Since the ion migration occurs on the picosecond time scale, the primary rearrangement of the glass network adjacent to an ionic site occurs at rates orders of magnitude higher than those of the critical minimum values, so the matrix demonstrates brittle–elastic response to the arising strain even at temperatures well above T g, which explains, among other things, why mixed alkali effect is observable in glass melts.

Tannic acid‐stabilized pericardium tissue: IR spectroscopy, atomic force microscopy, and dielectric spectroscopy investigations

Infrared (IR) spectroscopy, atomic force microscopy (AFM), and dielectric spectroscopy methods were employed to study structural and dynamic changes in the tannic acid (TA)-stabilized pericardium tissue. Chemically stabilized pericardium tissue is widely used in construction of the tissue derived bioprostheses. IR spectra recorded in the range 400-4000 cm-1 allowed us to recognize different types of TA-collagen interactions. Formation of hydrogen bonds between amine as well as amide NH groups from collagen and hydroxyl groups of TA was analyzed. The AFM imaging showed that the stabilization procedure with TA introduces considerable changes in both surface topography and thickness of collagen fibrils as well as in fibril arrangement on the tissue surface. It was found, that these structural changes have an impact on the dielectric behavior of the TA-stabilized tissue. The dielectric spectra for the native and TA-stabilized tissues were measured in the frequency and temperature ranges of 10(-1) -10(7) Hz and 120-270 K, respectively. The dielectric spectra revealed the relaxation process due to orientation of bound water supplemented by the fluctuation of collagen polar side groups. At the temperatures above approximately 210 K, the relaxation due to ion migration process was observed. It was found that both relaxation processes were influenced by the TA-collagen interaction.

Defect formation in Gd 3Fe 5O 12-based garnets: a Mössbauer spectroscopy study

The Mössbauer spectroscopy of Gd 2.2Pr 0.8Fe 5O 12 garnet, which exhibits higher electronic conduction with respect to Gd 3Fe 5O 12 due to the presence of Pr 4+ cations, showed that praseodymium doping decreases the coordination of Fe 3+ in octahedral sites. Penta-coordinated Fe 3+ ions, in combination with small quantities of Fe 4+, are also formed in the lattice of Gd 2.5Ca 0.5Fe 5O 12 where the variations of ionic and electronic transport properties indicate charge compensation via generation of oxygen vacancies and electron holes. The mechanisms of garnet lattice disorder, induced by acceptor- and donor-type doping, appear thus quite similar; in all cases, the ionic defect formation requires substantial structural reconstruction, probably associated with direct linking of iron–oxygen tetrahedra. Due to the low concentration of charge carriers and the important role of lattice relaxation in the oxygen ion migration processes, this behavior results in similar activation energies for the ionic conductivity in all Gd 3Fe 5O 12-based garnets.

Transport processes during electrowashing of filter cakes

Applications of electric fields during washing of filter cakes increases the removal rate of ions from the cake mother liquor, and under appropriate conditions the field also increases the wash flow rate by electroosmosis. Experimental data that show the key effects of the fields on the rates of ion mass transfer are presented: with the downstream electrode acting as a cathode, cation removal rates are increased whilst the removal rate of the anions is decreased. The concentration profile of the cations with washing time shows an increase in concentration to a value above that of the mother liquor, before it decreases due to displacement by the fresh wash liquor. A model is formulated that describes the advection, dispersion, ion migration and electroosmosis transport processes in the cake. Numerical solution of the model gives cation concentration profiles at the exit of the cake that are in qualitative agreement with the experimental observations. Experimentally measured wash liquor flow rates tend to be lower than what traditional colloid science principles predict by a factor of 5–10: reasons for this difference, supported by experimental work from other researchers, are discussed.

Concentration dependence of diffusion and migration of chloride ions: Part 2. Experimental evaluations

This paper series includes two parts: (1) theoretical considerations and (2) experimental evaluations. In Part 1, the chloride ion diffusion and migration processes in a pure solution system as well as in a solution-concrete system have been theoretically analyzed. The relationships between different diffusion coefficients from the conventional diffusion or migration tests have been established. In this, the second part, the parameters influencing the “effective” diffusion coefficient, such as activity coefficient, counter-electrical field, and the friction coefficient due to the ionic interaction, are quantitatively evaluated with available experimental data. The results show that the concentration dependence of chloride diffusion and migration can be quantitatively described by two decisive parameters: K τ and f; the former describes the effect of counter-electrical field and the latter describes the friction effect. The theories fit the experimental data fairly well. Some phenomena of ion diffusion in concrete can be explained by these theories, such as the differences in diffusion coefficient between diffusion and migration tests and between cations and anions.

Concentration dependence of diffusion and migration of chloride ions: Part 1. Theoretical considerations

This paper series includes two parts: (1) theoretical considerations and (2) experimental evaluations. In Part 1, the chloride ion diffusion and migration processes in concentrated solutions are theoretically analyzed. The quantitative relationship between diffusion coefficient and migration coefficient is established. Two important parameters that are inherent in the cement based materials (i.e., ion-selective semipermeability and chloride binding) are discussed. The theoretical analysis shows that the “effective” chloride diffusion coefficient determined from the conventional diffusion or migration tests is not a constant, but rather is a complicated function of concentration. This function contains four main factors: (1) the parameter K τ, describing the effect of counter-electrical potential; (2) the ratio of cation velocity to anion velocity β v ; (3) the friction coefficient f, which reflects the ionic interaction; and (4) the activity coefficient γ, which is also a function of concentration.

Advanced electrochemical methods for food can evaluation

Electrochemical measurements have been used to investigate the corrosion resistance of food cans produced from a steel–polymer laminate material, Ferrolite, over periods of up to 30 days. The aim of this work was to develop a predictive corrosion test procedure, whereby short term results could be used to predict long term container performance. Electrochemical impedance spectroscopy (EIS) and dc linear polarisation techniques were used to study the effect of increasing polymer laminate film thickness, and to compare Ferrolite performance with that of a conventional vinyl organosol lacquer. Testing was carried out using a sealed in electrode system, where electrodes were fitted to commercial can ends before filling. This electrode system was found to perform well over a 30 day period, and the results indicate that Ferrolite cans possessed a significantly greater resistance to corrosion than conventionally lacquered cans. Predictably, as the Ferrolite film thickness increased, coating and polarisation resistance values also increased. Under pack test conditions, coating and polarisation resistance parameters initially decreased rapidly, which is consistent with hydration and ion migration processes occurring within the film. After 30–40 days, the rate of change in resistance decreased and was consistent with longer term degenerative effects such as corrosion. Coating resistance, as determined by EIS, was found to be largely independent of the electrolytic oxygen concentration; however, polarisation resistance, determined by dc measurements, showed a strong inverse dependence on oxygen concentration.

Conductivity relaxation in phosphazene based polymer electrolytes

Electrical relaxation in Poly[bis ((methoxy ethoxy) ethoxy) phosphazene] (MEEP)-poly(ethylene oxide) (PEO)−(NaSCN) x have been studied using modulus spectroscopy in the temperature range 160−350 K and in the frequency range 10 Hz to 32 MHz. Two different types of relaxations are observed. The relaxation below 60°C is broad, nearly 2.3 decades in width whereas above 60°C narrow and symmetric (half width 1.4 decades) peaks are observed. The results have been explained on the basis of slower process of ion migration below the transition and a very fast one above it.

Diffusion Limited Percolation: A Model for Transport in Ionic Glasses

AbstractWe present a novel model for ionic transport in glasses which we call diffusion limited percolation. The model focuses on the fact that each mobile ion prefers and maintains its own distinct characteristic environment in the glassy network. This leads to mismatch effects and to the existence of a memory effect which strongly influences the process of ion migration. We show that by our simple model a variety of so far imperfectly understood phenomena can be explained, among them the drastic increase of the dc conductivity of oxide glasses with the modifier content and the mixed alkali effect.

Diffusion with memory: a model for mixed alkali effects in vitreous ionic conductors

The authors present a novel theory of the mixed alkali effect which focuses on the fact that each alkali prefers and maintains its own distinct characteristic environment in the mixed glass. This leads to mismatch between cations and sites recently occupied by unlike cations, and the existence of a memory effect which strongly influences the process of ion migration. This view of glass is consistent with both EXAFS and infrared measurements, and computer simulations reproduce the essential features of the mixed alkali effect including the mobility crossover and the conductivity minimum.

Impurity and Defect Center Concentrations in High-Purity Quartz: Their Change Processes by Sweeping and Irradiation

Effects of sweeping (electrodiffusion) and radiation on high-purity quartz are investigated, focusing on changes in impurity and defect center concentrations. The quantitative correlation between impurity and defect centers is estimated. Sweeping replaces Al–M (M=Na, Li, or K) centers with Al–OH centers by dissociating alkali ions in Al–M centers. The Al–OH center is produced initially at the anode and proceeds to the cathode. The relationship between the Al–OH formation process and the alkali ion migration process is consistent, as confirmed by their distribution measurements in several swept samples. It is confirmed that the number of removed alkali ions corresponds to the concentration of Al–M centers dissociated by sweeping. Removed alkali ions are both sodium and lithium. Irradiation produces not only Al–OH centers but also Al–h centers. However, the Al–h concentration is far smaller than the Al–OH concentration.

Influence of the electric double layer on glass leaching

When a glass comes into contact with water, an electric double layer forms at the glass-water interface. An analytical model that calculates the electric field and the resulting velocity of univalent alkali ions migrating in the glass matrix is developed. The ion migration velocity is calculated for an 85% SiO 2–15% Na 2O glass and for more complex glasses. The calculations indicate that the process of ion migration leads to normalized leach rates which are small compared to glass network dissolution rates.

Intrinsic stresses in anodic films on aluminium

Stresses in anodic barrier layers on aluminium were investigated by measuring the isothermal deformation of clamped membrane electrodes galvanostatically anodised on one side. At open circuit, the residual stresses were always tensile, independent of thickness within 250 nm and decreasing with current density from ca. 85 N/mm 2 at 1 mA/cm 2 to ca. 40 N/mm 2 at 0.05 mA/cm 2. The growing layers on the other hand exhibited compressive stresses predominantly caused by ion migration processes. The constant orders of magnitude were −20 N/mm 2 at 0.05 mA/cm 2 and −60 N/mm 2 at 0.2 mA/cm 2. At 1 mA/cm 2, however, a decrease from initially ca. −320 N/mm 2 to ca. −160 N/mm 2 at 240 nm was observed. This and the microscopically confirmed plasticity of growing oxides led to the outline of a growth model which was further tested by some preliminary measurements of the intrinsic forces present during the pore initiation in a phosphoric acid electrolyte.

Planar optical coupling elements for multimode fibers with two-step ion migration process

An electric field assisted two-step ion migration process in soda-lime glass plates has been used to produce optical couple waveguides with semicircular and circular cross sections. The radius and the numerical aperture of the guides are approximately the same as those of the graded index multimode fibers. A new coupler structure, the edge reflecting element, which could be used as an integrated demultiplexer in wavelength division multiplexing, has been fabricated. The loss spectrum of the waveguides is analyzed and a theoretical treatment of the ion concentrations is given.

Formation of Oxide Films at Platinum Anodes in Alkaline Solutions: II . Temperature Study

The kinetics of growth of oxide films at platinum anodes in solution is determined at different temperatures using the galvanostatic charging technique. The growth of the oxide film at potentials above about 1.0V vs.RHE follows the model of high field assisted formation of ions at the metal/ oxide interface and their migration within the oxide film. The activation energy and preexponential factor are determined as 18.5 kcal/mole and 1013cm−2, respectively. These parameters differ significantly from the respective values reported for the growth in acid solutions. Comparison of the growth kinetics in acid and alkaline solutions leads to a serious difficulty. Neither the process of ion formation at the metal/oxide interface, nor the process of ion migration through the oxide phase as the rate‐determining step, can account for the growth kinetics in alkaline solutions, unless it is assumed that different oxide phases form in acid and alkaline solutions. This is, however, an unlikely assumption.

Ion migration through cell membranes: Is it a process of diffusing corpuscles or diffracted ion matterwaves?

Justifications are presented for treating the process of ion migration through cell membranes not as a process of diffusing corpuscles but as a process of ion matterwaves being diffracted or reflected at the membrane corresponding to a permeable or an impermeable membrane. A qualitative explanation of the actions of anesthetics is given using the wave mechanical concept.

Zur Bestimmung der Beweglichkeit und Gleichgewichtskonstanten komplexierter Ionen mittels Gegenstromionenwanderung / Determination of the Mobilities and Stability Constants of Complex Ions by Means of Counter current Ion Migration

In a countercurrent ion migration process the ion of an element (e.g. a metal cation) can form various unstable complexes with the anion of the countercurrent electrolyte. The ion migrates then with an average mobility, which is a function of the mobilities and equilibrium constants of the equilibrated species. In order to hold a constant ionic strength and to establish various metal/ligand-ratios, a background ion must be mixed to the metal ion. In usual "statical" stationary distributions, in which neither the metal ion nor the background ion is transported, the ratio of the two can only be hold constant if their mobilities are very similar. This difficulty can be overcome if the background ion is transported with constant rate through a statical stationary distribution of the metal ion, and vice versa. The solution of the transport equation for such "dynamical" stationary distributions shows that the average mobility of the metal ion can be calculated if its concentrations in locally independent parts of the stationary distribution and in the overflow are measured. The mobilities and the equilibrium constants of the various complex species are then determined by means of known mathematical methods

Ion migration effects in r.f. “sputter cleaning” of dielectric films

We have shown that r.f. backsputtering or “sputter cleaning” of dielectric films may cause: (1) the transfer of impurities from one sample to another or from the substrate table to previously clean samples; and (2) ion migration effects within SiO 2 films which are expected to cause gross degradation of “sputter-cleaned” devices. Such degradation may not be annealable, since annealing does not cause the removal of mobile impurities, as has been shown previously. These results are in agreement with the previously presented theory of the ion migration process.

Zur Untersuchung von Gleichgewichten instabiler Komplexe und die Bestimmung der Beweglichkeiten der einzelnen Spezies mittels Gegenstrom-Ionenwanderung / Investigation of the Equilibrium of Unstable Complexes and the Determination of their Mobility by Means of Countercurrent Ion Migration

In a countercurrent ion migration process the ion of an element (e. g. a metal cation) can form various unstable complexes with the anion of the countercurrent electrolyte. The total concentration of such an element in its stationary and locally constant distribution in a countercurrent ion migration column is then determined by the average mobility of all equilibrated species containing this element. From stationary distributions in their dependence on concentration the mobilities of the various species can be determined if the constants of the different equilibrium stages are known and vice versa.