Structure and Electric Conductivity of (La,Sr)(Ga,Mg)O3-α Solid Electrolyte

Electric conductivity, Raman spectra, and thermal expansion of La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 solid solution (LSGM1218) based on lanthanum gallate were studied at various temperatures, and Xray phase analysis was performed at room temperature. Dilatometric measurements showed that secondorder phase transitions occur at 775±10$ and 880± 20 K. The transition around 880 K is confirmed by Raman spectra and by a change in the conductivity activation energy in this temperature range. This transition is associated with a symmetry change in the oxygen sublattice.     

Effect of the Electrode Potential on the Oxygen Reaction Rate in the Electrode System O2, Au/La0.88Sr0.12Ga0.82Mg0.18O2.85

The polarization dependences of a porous gold electrode in contact with a solid electrolyte of the composition La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 are studied at 600–800°C and oxygen pressures of 2 × 10⁻²-1 atm. It is shown that the rate of cathodic reduction of oxygen out of the gas phase depends on the preliminary treatment of the sample. The activation energy is equal to 110–135 kJ mol⁻¹ at a low polarization. After increasing the polarization, the activation energy for the cathodic reduction of oxygen equals 75–85 kJ mol⁻¹ and depends on the oxygen pressure as a power function with a power index of 1/4. The rate of the anodic evolution of oxygen is dependent neither on the preliminary treatment of the sample nor on the oxygen pressure in the gas phase and the polarization curve has a characteristic segment, which corresponds to a limiting overvoltage.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 954–962.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Beresnev.     

Electrode System Ni/Na y Al x V12O30/Al3+: An Impedance Spectroscopy Study

The impedance of electrochemical cells Ni/VOB/Al³⁺, Ni/VOB/Na⁺, and Ni/VOB/Ni (where VOB stands for vanadium oxide bronzes of the general formula Na _y Al _x V₁₂O₃₀, with 0 < x 1.7) is studied both at equilibrium and a constant-current polarization. Variations in the VOB composition and aqueous electrolytic solutions in contact with the bronze as a result of the passing of the current are monitored. The results of these measurements are employed to substantiate a model that describes the occurrence of processes of current production in the Ni/VOB/Al³⁺ electrode system. The overvoltage is defined to a substantial degree by the aluminum diffusion. The diffusion coefficients for aluminum, its partial conductivity, and transport number are estimated.     

Synthesis of dense ceramics of single-phase mayenite (Ca<Subscript>12</Subscript>Al<Subscript>14</Subscript>O<Subscript>32</Subscript>)O

The nanoporous material mayenite was synthesized by two methods: solid-phase and self-propagating high-temperature (combusting) (SHS) syntheses. The structure of the materials was determined by the X-ray diffraction analysis and IR and Raman spectroscopy.     

Polarisation conductivity of the O2,Pt/Zr(Y)O2 and H2-H2O, Pt/Zr(Y)O2 electrodes

Pt electrodes with defined contact geometries were studied by using impedance spectroscopy. The specific polarisation conductivity per unit length of the three-phase boundary was determined. It is found to be 1 × 10⁻⁴ S·cm⁻¹ at 977 °C in an atmosphere of “pure” hydrogen with an oxygen partial pressure of 10⁻²⁰ atm at 1000 °C. Investigations carried out in an atmosphere of pure oxygen revealed a pronounced dependence of the polarisation conductivity on the electrode history. The polarisation conductivity was found to be in a range of 2 × 10⁻⁴ to 6.5 × 10⁻⁴ S·cm⁻¹ at a temperature of 977 °C. It was possible to estimate the area of the electrolyte surface which takes part in the electrode reaction. The real exchange current density was determined.     

Thermal and electrical properties of Ca5Mg4−xZnx(VO4)6 (0 ≤ x ≤ 4)

Calcium vanadates Ca₅Mg_4−xZn_x(VO₄)₆ (0 ≤ x ≤ 4) have been studied for the first time using a set of high-temperature methods of analysis. The onset of melting process determined from differential scanning calorimetry decreases from 1158 to 881 °C (± 1.5 °C) with increasing of x (dopant’s content). CTE temperature dependence is found to show a hysteresis. Electrical transport properties measured by impedance spectroscopy in air of different humidity are also discussed. The value of electrical conductivity does not depend on air humidity. It is found to equal to 1.5 × 10⁻⁶ S cm⁻¹ at 720 °C for Ca₅Mg₄(VO₄)₆ which is specific for garnet-related crystals.

     

Polarisation resistance of the O2, Au/O2− and H2-H2O, Au/O2− electrode systems

Gold electrodes with known contact geometries were studied using impedance spectroscopy. From these data it was possible to determine the specific polarisation conductivity per unit length of three-phase boundary (TPB). The values were found to be (3÷22)×10⁻⁴ S·cm⁻¹ dependent on the electrode history in pure oxygen at 977 °C and 2×10⁻⁶ S·cm⁻¹ at 977 °C in “pure” hydrogen (P_O2=10⁻²⁰ atm at 1001 °C). The results are compared with previous data obtained for platinum electrodes.     

Polarization Conductance of the Electrode System O2, Au/0.9ZrO2–0.1Y2O3

An impedancemetry method is employed to investigate a porous gold electrode in contact with a solid oxygen-conducting electrolyte on the basis of zirconium dioxide of the same cationic composition, whose samples differ in the oxygen content. Upon reaching a stationary state, the interphase oxygen exchange rate is independent of the previous treatment and oxygen stoichiometry of the sample. The results are linked to the existence on the electrolyte surface of a layer whose structure differs from the bulk structure.     

Frequency dependence of conductivity of ethylene carbonate based electrolyte for Li-ion battery

Specific cell arrangement corresponding to four probe pouch cell with two reversible current and two indifferent potential electrodes is applied to study the existence of frequency dependence on conductivity of a medium between two potential electrodes, i.e., separator impregnated with electrolyte. It is established that frequency dependence of conductivity for carbonate-based electrolyte solution does exist. Series resistance is found to be in a good agreement by specific value with that reported earlier. Low frequency limit of impedance spectra is a few decimal orders higher than that of series resistance. Both low- and high-frequency resistances increase with the interelectrode distance in agreement with Ohm law.