Thermodynamics of Binary and Ternary Copper-, Cadmium,and Indium-Containing Semiconducting Phases: An Electrochemical Study

Optimum compositions of ion-selective membranes in quasi-binary systems CuCl-CdCl₂, LiCl-CdCl₂, and In₂S₃-InCl₃ are selected by a method of coulometric titration in cells with solid electrolytes. Transport numbers for ions are close to unity for the optimum compositions; transport numbers for electrons are vanishingly small ( ≺10⁻³ to 10⁻⁴); the electroconductivity is equal to ≈ 10⁻³ S cm⁻¹ at 200°C; the diffusion coefficients for the current-producing component are on the order of 10⁻⁶ to 10⁻⁷ cm² s⁻¹. When using a solid electrolyte of the composition CuCl-CdCl₂, which contains 30 mol % CdCl₂, methods of emf and electroconduction reveal that the region of homogeneity of copper(I) selenide falls in the region of compositions Cu_1.33Se-Cu_2.67Se.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 721–727.Original Russian Text Copyright © 2005 by Leushina, Kolesnikova, Makhanova, Zlomanov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Electrochemical sensors for sulfur- and lead-containing gases

The possibility of using solid-electrolyte transducers with nonstoichiometric electrodes was studied, and the effect of the material and nonstoichiometry of lead monochalkogenides as measurement electrodes on the work of transducers was considered. The reliability of the results obtained was substantiated by comparing the calculated thermodynamic properties of the measurement electrodes with the corresponding reference values. The effect of nonstoichiometry was assessed from coulometric titration curves. It was noticed that the defect type affects the sensitivity of the transducer. The effect of the surface of the measurement electrode on the process of gas analysis was assessed. The applicability region for the transducers under study was indicated.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 193–197.Original Russian Text Copyright © 2005 by Leushina, Makhanova.Presented at the International Forum Analytics and Analysts, Voronezh, 2003.This revised version was published online in April 2005 with corrections to the author names and book review format.     

Selecting indium-containing systems as solid electrolytes

Quasi-binary salt systems InCl₃-MeCl₂, where Me²⁺ stands for Mg²⁺, Cd²⁺, Zn²⁺, Sn²⁺, Co²⁺, or Mn²⁺, in the region of solid solutions on the basis of InCl₃ are considered. A comparative characteristic of some transport properties of these systems is given and optimum compositions for all systems under consideration are determined. The conduction mechanism that presumably takes place in systems InCl₃-MgCl₂ and InCl₃-CdCl₂ is confirmed by data that are obtained with the aid of the Tubandt method. In order to raise the reversibility with respect to the indium ion, also considered is the In₂S₃-InCl₃ system, in which the basis compound is In₂S₃. Methods of electroconduction and XRD are used to establish the existence of a region of limited solid solutions on the basis of indium sulfide. The current efficiency in a system with solid electrolyte In₂S₃-InCl₃ is determined (CE > 50%) and the dependence of the current efficiency on the electrolysis regime is considered. Thermodynamic investigation of some indium-containing compounds and the doping with indium are conducted with use made of indium-containing solid electrolytes of optimum compositions. Data concerning the magnitude of the alteration occurring in the Gibbs energy during the formation of indium-containing semiconducting compounds, which are close to reference data, are obtained.     

Development of Methods for the Production of Electrodes of Nonstoichiometric Compositions for Solid-Electrolyte Sensors with Predictable Sensitivity

The feasibility of application of sensor Me|Pb|PbCl₂-CaCl₂|Pb_{1 ± δ}|Me, where X = Se, Te, in an analysis of lead-containing gaseous environment is considered. The effect of the nature of the material, its nonstoichiometry, and the defect structure of measuring electrodes on the operation characteristics of these sensors is discussed. The mechanism of the formation of defects during the insertion of an electrochemically active component into the material of the measuring electrode is refined. The limiting stage of a process of a gas analysis is determined.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 728–734.Original Russian Text Copyright © 2005 by Leushina, Makhanova, Orzhaeva, Zlomanov.Published on the basis of a contribution delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Sorption Catalytic Determination of Copper(II) and L-α-alanine on Mg-, Al-Layered Double Hydroxides

Mg-, Al and Mg-, Cu-, Al-layered double hydroxides well-known synthetic hydrotalcite-like sorbents, were used for the first time as carriers for indicators in the sorption catalytic determination of copper(II) and L-α-alanine. Mg-, Al and Mg-, Cu-, Al-layered double hydroxides were synthesized by coprecipitation and characterized using infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The adsorption of 0.50?mg?L^?1 copper(II) solution by Mg-, Al-layered double hydroxides followed a pseudo-second-order model with an equilibrium sorption capacity of 24.2?×?10^?3?mg?g^?1 (3.8?×?10^?4?mmol g^?1) and a reaction rate constant of 4.2?g mg^?1?min^?1. Mg-, Al-layered double hydroxide tablets were prepared and used for sorption concentration and subsequent sensitive and selective sorption catalytic determination of 5.5?×?10^?3 to 1.0?mg?L^?1 copper(II) at the sorbent phase. The method was used for the analysis of natural water. A method was developed for the determination of α-alanine in Mg-, Cu-, Al-layered double hydroxide tablets with a limit of detection of 4.0?×?10^?3 mol?L^?1. In addition, thin layers of Mg-, Cu-, Al-layered double hydroxide were used to separate α-alanine and determine α-amino acids by thin-layer chromatography.     

Determination of the Selectivity of Electrodes Made of a Mixture of Nonstoichiometric Silver and Copper(I) Sulfides in the Analysis of Sulfur-Containing Aqueous Solutions

The possibility of using electrodes made of a mixture of nonstoichiometric silver and copper(I) sulfides in the analysis of sulfur-containing aqueous solutions by direct potentiometry and potentiometric titration was assessed. The selectivity coefficients of the electrodes under study to chloride and iodide ions were determined. The effect of pH on the performance and conductivity of electrodes was studied.     

Nonstationary probabilities and time correlation functions for an asymmetric exclusion process

We give the complete solution of the master equation for a system of interacting particles with finite density. We obtain the solution using a new form of the Bethe ansatz for an asymmetric simple exclusion process on the ring. We first find the one-point time correlation function for the discrete version of the process. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 146, No. 3, pp. 499–508, March, 2006.     

Electrochemical Sensors for Sulfur- and Lead-Containing Gases: Effect of Nonstoichiometry of Measuring Electrodes

In accordance with the fact that the region of homogeneity of lead sulfide is two-sided, i.e. it includes compositions with both sulfur excess and lead excess relative to the stoichiometric composition, it is shown that a sensor with a Pb_{1 ±} S measuring electrode (ME) may be used for analyzing both sulfur- and lead-containing media. The general principle of operation of electrochemical sensor Me, Pb/PbCl₂–CaCl₂/Pb_{1 ±} S, is based on measuring EMF of an electrochemical circuit with a lead-conducting electrolyte at a specified sulfur vapor pressure above the reference electrode. At a fixed temperature, the cell's EMF is uniquely defined by the sulfur content on ME. The studies are done in the temperature interval 285 to 300°C where characteristics of the solid electrolyte used are optimum; its upper boundary is limited by mp of the lead reference electrode (327°). The interval of determinable concentrations of sulfur- and lead-containing gases is 10^–1 to 10^–9 vol %. If analysis is performed in a dynamic mode (in a carrier gas flow), the limiting stage is the adsorption of gas molecules on the ME surface and the sensor sensitivity increases after modifying the surface by various techniques and also due to the ME composition altering only in a surface layer. The sensor's working characteristics are affected mostly by the degree of deviation of the ME material from stoichiometry.