Ion Transfer in CdF<Subscript>2</Subscript>-based Iso- and Polyvalent Solid Solutions

The ionic conductivity of solid solution Cd_0.77Sr_0.23F₂ is 1.6 × 10⁻⁴ S/cm at 500 K. The conduction mechanism changes from a vacancy mechanism to an interstitial one at 523–553 K. In solid solutions Cd_0.9R_0.1F_2.1 (R = La-Lu, Y), the activation enthalpy of conduction decreases from 0.9 to 0.8 eV with decreasing ionic radius of R³⁺, raising the 500-K conductivity from 6 ×10⁻⁶ S/cm for La³⁺to 6 × 10⁻⁵ S/cm for Lu³⁺. For crystalline Cd_0.95In_0.05F_2.05, ionic and electronic conductivities at 313 K equal 5 × 10⁻⁴ and 5 − 10⁻⁶ S/cm.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 627–632.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Sul’yanova, Sobolev.     

Solid Electrolytes Based on KAlO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>: The Crystalline Structure and Conduction

The structure of solid high-conductance potassium electrolytes K_{1 − x} Al_{1 − x} Ti_xO₂ (x = 0.1; 0.2) at 25 and 575°C is studied by a powder neutron diffraction analysis with the application of full-profile Rietveld analysis. Inserting titanium ions removes in potassium aluminate the phase transition at 540°C and the conductance anisotropy typical for its low-temperature form. Both structures are identical (fcc lattice, space group Fd3m). Experiment and calculation coincide best under the assumption that the potassium sublattice is disordered. The conductance increase upon inserting ions Ti⁴⁺ is due, apart from stabilization of the fcc structure, to formation of additional potassium vacancies and larger channels for the migration of potassium cations (ions Ti⁴⁺ are larger than ions Al³⁺).__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 878–883.Original Russian Text Copyright © 2005 by Burmakin, Voronin, Akhtyamova, Berger, Shekhtman.     

Ionic conduction of a high-temperature modification of Lu<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

A nanoceramic product of the composition Lu₂Ti₂O₇ is synthesized by a coprecipitation method with a subsequent sublimation drying and an annealing at 650–1650°C. The conduction of Lu₂Ti₂O₇ synthesized at 1650°C is ionic (10^–3 S cm^–1 at 800°C). Thus, a new material with a high ionic conduction has been discovered. The ordering in Lu₂Ti₂O₇ is studied by methods of RFA, RSA, IK spectroscopy, electron microscopy, and impedance spectroscopy. The existence of a low-temperature phase transition fluorite-pyrochlore at 800°C and a high-temperature conversion order-disorder at 1650°C are established.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 298–303.Original Russian Text Copyright © 2005 by Shlyakhtina, Ukshe, Shcherbakova.     

Conductivity studies of dense yttrium-doped BaZrO3 sintered at 1325 °C

High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10⁻² S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Ω cm² therefore thin film electrolytes are required for successful application. As BaZrO₃-based materials have to be sintered at temperatures as high as 1700 °C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO₃-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr_0.8Y_0.2O_2.9 was successfully sintered at 1325 °C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr_0.8Y_0.2O_2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba_0.97Zr_0.77Y_0.19Zn_0.04O_3−δ which exhibits a tetragonal structure with space group P4/mbm (127); a=5.9787(1) Å, c=4.2345(1) Å, V=151.36(1) Å³. It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H₂/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba_0.97Zr_0.77Y_0.19Zn_0.04O_3–δ is 1.0×10⁻³ S/cm above 600 °C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insignificant at high temperature for the well-sintered sample.     

Three Forms of the Misfit Layered Cobaltite [Ca2CoO3] [CoO2]1.62·A 4D Structural Investigation

Three misfit layer compounds with the same chemical formula Ca₃Co_4−xO_9+δ were isolated in the Ca–Co–O system. They exhibit either a monoclinic or an orthorhombic symmetry. These crystals are constituted of two interpenetrating C sublattices showing incommensurate periods along the b axis. The structure of the three crystals can be described as an alternate stacking along [001] of distorted rock-salt-type slabs [Ca₂CoO₃] and of [CoO₂] layers displaying a distorted CdI₂-type structure. Relating to the symmetry and the different observed c periods, different sequences are found for the [CoO₂] layers running along [001] within the three crystals. Two of them were determined by single X-ray diffraction using the 4D superspace formalism. A significant displacive modulation is implied, acting mainly on Ca and O atoms involved in the intersystem bonding scheme. This modulation leads to a noticeable distortion of the CoO₆ octahedra of the [CoO₂] layers. Strong interactions, via Ca–O bonds, are evidenced between the two sublattices. A systematic positional disorder is observed inside the [CoO] layer.     

A study of the perovskite solid solution series LaxSr1−xRuO3 and LaxCa1−xRuO3 by ruthenium-99 Mössbauer spectroscopy

The magnetic, electronic, and structural properties of the solid solutions La_xSr_1−xRuO₃ and La_xCa_1−xRuO₃ have been studied by ⁹⁹Ru Mössbauer spectroscopy and other techniques. The La_xCa_1−xRuO₃ phases are reported for the first time and have been shown by powder X-ray diffraction measurements to be orthorhombically distorted perovskites. Electrical resistivity measurements on compacted powders show that all the phases are metallic with p 10⁻³, ohm-cm. Progressive substitution of Sr²⁺ by La³⁺ in ferromagnetic SrRuO₃ leads to a rapid collapse of the magnetic hyper-fine splitting at 4.2°K. For x = 0.25 some ruthenium ions still experience a magnetic field but for 0.4 x 0.75 only single, narrow resonance lines are observed, consistent both with the complete removal of the ferromagnetism and with the presence of an averaged ruthenium oxidation state in each phase, i.e., La_x³⁺Sr_1−x²⁺Ru^(4−x)+O₃ rather than La_x³⁺Sr_1−x²⁺Ru_x³⁺Ru_1−x⁴⁺O₃. LaRuO₃ and CaRuO₃ both give essentially single-line spectra at 4.2°K, indicating that the ruthenium ions in these oxides are not involved in long-range antiferromagnetic order but are paramagnetic. The solid solutions La_xCa_1−xRuO₃ (0 < x 0.6) give sharp symmetrical singlets with chemical isomer shifts (relative to the Ru metal) which move progressively from the value characteristic of Ru⁴⁺ (−0.303 mm sec⁻¹) toward the value for Ru³⁺ (−0.557 mm sec⁻¹), consistent with the presence of intermediate ruthenium oxidation states in these phases also.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Temperature dependence of the polarization resistance of the O<Subscript>2</Subscript>,Au/La<Subscript>0.88</Subscript>Sr<Subscript>0.12</Subscript>Ga<Subscript>0.82</Subscript>Mg<Subscript>0.18</Subscript>O<Subscript>2.85</Subscript> electrode system

The impedance of a porous gold electrode in contact with solid electrolyte La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 and the effect of the manufacture conditions on its polarization resistance are studied at 600–800°C in air. The overall oxygen reaction rate on a gold electrode is described as the sum of two partial constituents, namely, the oxygen exchange at the gas/electrolyte interface at the gold/gas/electrolyte triple-phased boundary.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 190–197.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Khlupin, Beresnev.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Preparation of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> by polyacrylamide gel processing and its thermoelectric properties

Ca₃Co₄O₉ powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric properties of Ca₃Co₄O₉ ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10⁻⁴ W m⁻¹ K⁻² at 700 °C, which is larger than that of Ca₃Co₄O₉ ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily scaled up chemical route to improve the thermoelectric properties of Ca₃Co₄O₉ ceramics by preparing the homogeneous and pure Ca₃Co₄O₉ phase.     

Microstructure and Conduction of Composites Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi₂CuO₄ + xBi₂O₃ (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi₂CuO₄, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi₂O₃ and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi₂CuO₄ crystallites.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 596–601.Original Russian Text Copyright © 2005 by Lyskov, Metlin, Belousov, Tret’yakov.     

Sr2NiMoO6−δ as anode material for LaGaO3-based solid oxide fuel cell

The double-perovskite Sr₂NiMoO_6−δ (SNMO) was investigated as an anode material of a solid oxide fuel cell (SOFC). With a 300 μm thick La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−σ (LSGM) disk as electrolyte and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ as the cathode, the SNMO anode showed power densities of 819 mW cm⁻² in hydrogen at 1123 K. Moreover, there was no buffer layer between anode and electrolyte, which would reduce design techniques and save design cost. After test no chemical reaction was discovered between anode and electrolyte. The anode exhibited good conductivity and the value was around 60 S cm⁻¹ in H₂. Also it had almost linear thermal expansion from room temperature to 1253 K and the average thermal expansion coefficient was about 12.14 × 10⁻⁶ K⁻¹, which was quite close to that of La_0.9Sr_0.lGa_0.8Mg_0.2O₃ (12.17 × 10⁻⁶ K⁻¹) electrolyte.     

ESR Study of the Formation of O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> Radical Anions on Oxidized CeO<Subscript>2</Subscript> and CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> Adsorbing a CO + O<Subscript>2</Subscript> Mixture

It is demonstrated by ESR measurements that O ₂ ⁻ (CO + O₂) radical anions result from CO + O₂ adsorption on the oxidized surface of CeO₂. These radical anions are stabilized in the coordination sphere of Ce⁴⁺ cations located in isolated and associated anionic vacancies. This reaction shows an activation behavior determined by CO adsorption. The variation of O ₂ ⁻ (CO + O₂) concentration with CO adsorption temperature suggests that surface carbonates and carboxylates participate in this reaction. In the (0.5– 10.0)%CeO₂/ZrO₂ system, O ₂ ⁻ forms on supported CeO₂ and is stabilized on Ce⁴⁺ and Zr⁴⁺ cations. The stability of O ₂ ⁻ -Ce⁴⁺ complexes is lower on supported CeO₂ than on unsupported CeO₂, indicating a strong interaction between the cerium cations and the support.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 423–429.Original Russian Text Copyright © 2005 by Il’ichev, Kuli-zade, Korchak.     

Investigation on double perovskite Ba4Ca2Ta2O11

The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba₄Ca₂Ta₂O₁₁ have been investigated. Ba₄Ca₂Ta₂O₁₁ crystallizes in the cryolite structure (cubic, Fm3m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H₂O per mol Ba₄Ca₂Ta₂O₁₁. In moist air, the structure symmetry becomes monoclinic (C2/m) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200–400 °C, the protonic conduction is prevailing with an activation energy E_A = 0.85 eV. In the intermediate temperature range (400–600 °C), O²⁻ anionic and protonic conductions are mixed with an activation energy E_A = 0.45 eV and in the third region, for temperatures above 600 °C, O²⁻conduction is prevailing with an activation energy E_A = 0.85 eV.     

Structure and Properties of Solid Solutions in the System YBaCuFeO<Subscript>5</Subscript>-YBaCuCoO<Subscript>5</Subscript>

The crystal structure parameters of solid solutions YBaCuFe_{1 − x} Co_xO₅ (0 ≤ x ≤ 1) were determined, and their thermal stability, thermal expansion, conductance, thermoelectromotive force, dielectric properties, and magnetic sensibility were studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 716–720.Original Russian Text Copyright © 2005 by Chizhova, Klyndyuk, Bashkirov, Petrov, Yanushkevich.     

On the Possibility of Using Protonic Solid Electrolyte CsHSO<Subscript>4</Subscript> in Hydrogen Fuel Cells

Electrochemical parameters of an H₂|air fuel cell with a membrane of solid electrolyte CsHSO₄ or composites (1 − x)CsHSO₄/xSiO₂ (x = 0.1–0.3) and different electrodes are measured at 175 °C. The maximal power (3.5 mW/cm² at a voltage of 0.6 V) is obtained for a cell with platinum-black electrodes and an intermediate layer of a mixture of platinum black and the electrolyte material. In the absence of a platinum catalyst, CsHSO₄ and composites CsHSO₄/SiO₂ are chemically stable in hydrogen at the operating temperature of the fuel cell.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 556–559.Original Russian Text Copyright © 2005 by Lavrova, Russkikh, Ponomareva, Uvarov.     

Synthesis and structure analysis of tetragonal Li7La3Zr2O12 with the garnet-related type structure

We have successfully synthesized a high-purity polycrystalline sample of tetragonal Li₇La₃Zr₂O₁₂. Single crystals have been also grown by a flux method. The single-crystal X-ray diffraction analysis verifies that tetragonal Li₇La₃Zr₂O₁₂ has the garnet-related type structure with a space group of I4₁/acd (no. 142). The lattice constants are a=13.134(4) Å and c=12.663(8) Å. The garnet-type framework structure is composed of two types of dodecahedral LaO₈ and octahedral ZrO₆. Li atoms occupy three crystallographic sites in the interstices of this framework structure, where Li(1), Li(2), and Li(3) atoms are located at the tetrahedral 8a site and the distorted octahedral 16f and 32g sites, respectively. The structure is also investigated by the Rietveld method with X-ray and neutron powder diffraction data. These diffraction patterns are identified as the tetragonal Li₇La₃Zr₂O₁₂ structure determined from the single-crystal data. The present tetragonal Li₇La₃Zr₂O₁₂ sample exhibits a bulk Li-ion conductivity of σ_b=1.63×10⁻⁶ S cm⁻¹ and grain-boundary Li-ion conductivity of σ_gb=5.59×10⁻⁷ S cm⁻¹ at 300 K. The activation energy is estimated to be E_a=0.54 eV in the temperature range of 300–560 K.     

Effect of Copper on Solid Electrolytes (Ce0.8Sm0.2)1 ? xCuxO2 ? δ and Composite Cathodes Based on La0.8Sr0.2MnO3

The phase composition and electroconduction in air of solid electrolytes (Ce_0.8Sm_0.2)_{1 − x} Cu_xO_{2 − δ} (CSCu), where x = 0, 2, 5, 10, and 20 mol % and which are synthesized using the ceramic technology, are studied. Adding an additive of CuO lowers the CSCu sintering temperature by 100– 200°C and leads to the formation of single-phase solid solutions of a fluorite type up to x = 10 mol %. The electroconductivity of the CSCu electrolytes remains practically invariant upon adding up to 5 mol % Cu and equals 0.089–0.095 and 0.017–0.021 S cm⁻¹ at 800 and 600°C. The sintering, adhesion, and electroconductance of composite cathodes based on La_0.8Sr_0.2MnO₃ with 40% CSCu and their electrochemical behavior in air in the temperature interval 900–1000°C on carrying electrolyte Zr^0.9Y_0.1O_1.95 with a CSCu sublayer containing 2 mol % Cu are studied.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 656–661.Original Russian Text Copyright © 2005 by Bogdanovich, Gorelov, Balakireva, Dem’yanenko.     

Superionic Conduction in Complex Fluorides of Antimony(III) MnSbxFy (M—Cations of an Alkali Metal, Ammonium, or Thallium, n = 1–3, and x = 1–4)

Methods of ¹⁹F NMR and impedance spectroscopy are used to investigate the internal mobility of fluoride (ammonium) ions and electrophysical characteristics of complex trivalent antimony fluorides MSb₄F₁₃, MSb₃F₁₀, MSb₂F₇, M₂Sb₃F₁₁, M₃Sb₄F₁₅, and MSbF₄ (M is an alkali cation, ammonium, thallium). The ion motion types in the cationic and anionic sublattices of the fluorides are determined at 150–500 K. The polymorphous transformations in the fluorides are usually phase transitions to a superionic state and their high ionic (superionic) conductivity (σ ≥ 10⁻⁴ to 10⁻² S cm⁻¹ at 400 K) is due to the diffusion motion of ions of fluoride, ammonium, and possibly sodium, potassium, and thallium. The high polarizability of thallium ions favors the development of high mobility of fluoride ions in the fluorides.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 560–572.Original Russian Text Copyright © 2005 by Kavun, Uvarov, Slobodyuk, Brovkina, Zemnukhova, Sergienko.     

Preparation and electrical properties of new oxide ion conductors Ce6−xDyxMoO15−δ (0.0 ≤ x ≤ 1.8)

Ce_6−xDy_xMoO_15−δ (0.0 ≤ x ≤ 1.8) were synthesized by modified sol–gel method. Structural and electrical properties were investigated by means of X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The XRD patterns showed that the materials were single phase with a cubic fluorite structure. Impedance spectroscopy measurement in the temperature range between 350 °C and 800 °C indicated a sharp increase in conductivity for the system containing small amount of Dy₂O₃. The Ce_5.6Dy_0.4MoO_15−δ detected to be the best conducting phase with the highest conductivity (σ_t = 8.93 × 10⁻³ S cm⁻¹) is higher than that of Ce_5.6Sm_0.4MoO_15−δ (σ_t = 2.93 × 10⁻³ S cm⁻¹) at 800 °C, and the corresponding activation energy of Ce_5.6Dy_0.4MoO_15−δ (0.994 eV) is lower than that of Ce_5.6Sm_0.4MoO_15−δ (1.002 eV).     

Charge Transport in BaCe<Subscript>0.85</Subscript>R<Subscript>0.15</Subscript>O<Subscript>3 − δ</Subscript> (R = Sm,Pr, Tb) in Oxidizing and Reducing Environment

Overall conductance (in moist and dry air at partial water vapor pressures of 2.34 and 40 Pa, below 970° C) and transport numbers for ions and protons in ceramics BaCe_0.85R_0.15O_{3 − δ} doped by cations with constant (R = Sm) and variable (R = Pr, Tb) oxidation degrees and in BaCeO₃ are measured. Partial conductances (by ions, protons, oxygen ions, holes) are determined in moist air at partial oxygen pressures of 10⁵–10⁻¹³ Pa at 900°C. Various models for the hydrogen incorporation in the oxides under study are discussed.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 748–754.Original Russian Text Copyright © 2005 by Sharova, Gorelov, Balakireva.