Ionic Conductivity

Photoelectrochemical Hydrogen Production System Using Li-Conductive Ceramic Membrane

Based on the LiLaTiO₃ compound, a ceramic membrane for a photoelectrochemical cell was created. The microstructure, phase composition, and conductivity of a semiconductor photoelectrode and a ceramic membrane were studied by using various experimental methods of analysis. A ceramic Li conducting membrane that consisted of Li_0.56La_0.33TiO₃ was investigated in solutions with different pH values. The fundamental possibility of creating a photoelectrochemical cell while using this membrane was shown. It was found that the lithium-conductive membrane effectively works in the photoelectrochemical system for hydrogen evolution and showed a good separating ability. When using a ceramic membrane, the pH in the cathode and anode chambers of the cell was stable during 3 months of testing. The complex impedance method was used to study the conductive ceramic membrane in a cell with separated cathode and anode chambers at different pH values of the electrolyte. The ceramic membrane shows promise for use in photoelectrochemical systems, provided that its resistivity is reduced (due to an increase in area and a decrease in thickness).

Fast ion transport for synthesis and stabilization of β-Zn4Sb3

Mobile ion-enabled phenomena make β-Zn₄Sb₃ a promising material in terms of the re-entry phase instability behavior, mixed electronic ionic conduction, and thermoelectric performance. Here, we utilize the fast Zn²⁺ migration under a sawtooth waveform electric field and a dynamical growth of 3-dimensional ionic conduction network to achieve ultra-fast synthesis of β-Zn₄Sb₃. Moreover, the interplay between the mobile ions, electric field, and temperature field gives rise to exquisite core-shell crystalline-amorphous microstructures that self-adaptively stabilize β-Zn₄Sb₃. Doping Cd or Ge on the Zn site as steric hindrance further stabilizes β-Zn₄Sb₃ by restricting long-range Zn²⁺ migration and extends the operation temperature range of high thermoelectric performance. These results provide insight into the development of mixed-conduction thermoelectric materials, batteries, and other functional materials.

β-Zn₄Sb₃ has promising thermoelectric performance, but its ionic migration properties make it prone to degradation. Here the authors exploit the ion migration in an electric field-assisted synthesis method, fast producing β-Zn₄Sb₃ with improved phase stability and extended temperature range for the thermoelectric operation.

Oxygen thermomigration in acceptor-doped perovskite

The recent proposal of possible oxygen-thermomigration as a plausible mechanism for unipolar resistive switching of oxide memristors is now widely employed in modelling or simulating their memristive function on the grounds of the conventional picture that the mobile component O is always thermophobic, with its reduced heat-of-transport being equal to its migrational enthalpy (q_O* = ΔH_m > 0). At 1000 °C, we measured the thermomigration of mobile-component O in a prototype memristive perovskite, CaTi_0.90Sc_0.10O_2.95+δ, across its near-stoichiometric regime (δ ≈ 0), where oxygen vacancy concentration is essentially fixed by doping acceptor impurities (i.e., ). It has been found that the reduced heat-of-transport of mobile O (q_O*) varies systematically in the range of -2 < q_O*/eV ≤ +2, as the composition varies from hypo-(δ < 0) to hyper-stoichiometry (δ > 0), exhibiting a sign reversal or thermomigration direction change from thermophilic (q_O* < 0) to thermophobic (q_O* > 0). This sign-reversal is attributed to the change in the electronic ambipolar company of from electrons to holes crossing the stoichiometric composition δ = 0. The numerical data for q_O* together with the measurement details are reported.

Solid State Ionics: from Michael Faraday to green energy-the European dimension

Solid State Ionics has its roots essentially in Europe. First foundations were laid by Michael Faraday who discovered the solid electrolytes Ag2S and PbF2 and coined terms such as cation and anion, electrode and electrolyte. In the 19th and early 20th centuries, the main lines of development toward Solid State Ionics, pursued in Europe, concerned the linear laws of transport, structural analysis, disorder and entropy and the electrochemical storage and conversion of energy. Fundamental contributions were then made by Walther Nernst, who derived the Nernst equation and detected ionic conduction in heterovalently doped zirconia, which he utilized in his Nernst lamp. Another big step forward was the discovery of the extraordinary properties of alpha silver iodide in 1914. In the late 1920s and early 1930s, the concept of point defects was established by Yakov Il'ich Frenkel, Walter Schottky and Carl Wagner, including the development of point-defect thermodynamics by Schottky and Wagner. In terms of point defects, ionic (and electronic) transport in ionic crystals became easy to visualize. In an 'evolving scheme of materials science', point disorder precedes structural disorder, as displayed by the AgI-type solid electrolytes (and other ionic crystals), by ion-conducting glasses, polymer electrolytes and nano-composites. During the last few decades, much progress has been made in finding and investigating novel solid electrolytes and in using them for the preservation of our environment, in particular in advanced solid state battery systems, fuel cells and sensors. Since 1972, international conferences have been held in the field of Solid State Ionics, and the International Society for Solid State Ionics was founded at one of them, held at Garmisch-Partenkirchen, Germany, in 1987.

A Mechanistic Approach to Conductivity Relaxation in Ionic Glasses

A mechanism is proposed for conductivity relaxation in ionic glasses, based on the operation of a memory effect (as postulated in the dynamic structure model) that provides the necessary synergy for ‘pair-wise’ coupling of ionic motions in single cation glasses. It is suggested that this mechanism (which resembles in some respects the older ‘interstitialcy’ process) constitutes an essential component of the single and many-particle reaction route’ in Funke’s concept of mismatch and relaxation (CMR). This coupling is also present in mixed cation glasses, but the appearance of a site mismatch effect and the consequent disappearance of synergy leads to anomalous behaviours typical of the mixed cation effect, including recently reported increases in activation volume.

The Advent of Solid-State Thermodynamics, Kinetics and Electrochemistry in the 20thCentury

This paper summarizes some of the early history of physical chemistry of solids. It describes the consequences of the experimental and conceptual development. It illustrates the diversifications of the field, and it points out the enormous impact on modern technology and life.

The thermoelectric power of ionic crystals II. Results for potassium chloride

The thermoelectric power of single crystals of pure potassium chloride and of potassium chloride containing 107 x 10 -5 mole fraction of strontium chloride has been measured in the temperature range 561 to 693 °C, platinum electrodes being used. The results for pure potassium chloride differ substantially from the value reported by Nikitinskaya & Murin (1955) and show much less experimental scatter. A large potential produced by the crystals in the absence of a temperature gradient in the temperature range 470 to 570 °C is briefly described. From the theory of thermoelectric power proposed by Allnatt & Jacobs (1961) the heat of transport of the cation is found to be 0*99 eV and that of the anion 2 J eV in the temperature range 560 to 690 °C. Reasons are discussed for the failure of the relation proposed by Holtan, Mazur & de Groot (1953), which implies that the sum of the heats of transport should be zero for pure potassium chloride.

Electrodiffusion (sweeping) of ions in quartz-a review

Sweeping, a high-temperature process that selectively exchanges monovalent ions in quartz, is reviewed. Sweeping is used commercially to replace interstitial alkalis with hydrogen. Electrodiffusion improves the radiation hardness of quartz oscillator crystals and lowers the etch channel density. Sweeping affects the substitutional aluminum with its associated alkali and the extended dislocation networks with their precipitated impurities. At high temperatures the interstitials are freed and swept down the open Z-axis channels by an applied electric field. These interstitials can then be swept out at the negative electrode, provided replacement ions, usually hydrogen, are brought in at the positive electrode. Thus, the alkali associated with the aluminum is replaced by a hydrogen, and the precipitates in the dislocation networks are modified so that they are less reactive to the etchants. With the field applied at a room temperature, a peak or plateau in the sample current is observed during warm-up near 250-300 degrees C, followed by a decay at the 500 degrees C sweeping temperature. When the current becomes steady, the sweeping is thought to be complete. While infrared and high-temperature resistance measurements are useful, EPR techniques seem to provide the most reliable test for complete ion exchange at the aluminum site.