Solid State Ionics (v.178, #5-6)

Dielectric relaxation measurements for Y2O3-stabilized ZrO2 single crystals with different directions have shown anisotropic dielectric properties and approved the anisotropic diffusion paths of oxygen ions in fluorite structures suggested by neutron diffraction measurements. The activation energy including the migration energy of mobile oxygen ions obtained from the dielectric measurements suggested that oxygen ions easily diffuse along the 〈100〉 direction. The amount of mobile oxygen ions is also highest in the direction. The anisotropic dielectric properties are discussed along with the diffusion path of oxygen ions in fluorite structures.
Keywords: Fluorite structure; YSZ; Oxygen ionic conductor; Dielectric property;

Ab initio electronic structure calculation of oxygen vacancies in rutile titanium dioxide by Faruque M. Hossain; G.E. Murch; L. Sheppard; J. Nowotny (319-325).
The electronic structure of rutile TiO2 −  x is studied using first-principles density functional theory (DFT) calculations. Nonstoichiometry in rutile TiO2 due to defects in the form of oxygen vacancies leads to a considerable change in the electronic structure. In this paper, we calculate the band structure, density of states, and orbital energy distribution in a reduced (oxygen deficient) TiO2 −  x for different concentrations of oxygen vacancies (x). Energy levels are found to appear inside the forbidden energy region either as an isolated form of bands at different energy levels or merged with the conduction band depending on the value of x and the size of the super cells.
Keywords: Electronic structure; Titanium dioxide; Nonstoichiometry; Point defects;

Epitaxial Pt(111) thin film electrodes on YSZ(111) and YSZ(100) — Preparation and characterisation by G. Beck; H. Fischer; E. Mutoro; V. Srot; K. Petrikowski; E. Tchernychova; M. Wuttig; M. Rühle; B. Luerßen; J. Janek (327-337).
Platinum films with thicknesses up to 1 μm have been deposited on YSZ(111) and on YSZ(100) by pulsed laser deposition (YSZ: yttria-stabilized zirconia). The as-deposited platinum films are nanocrystalline with a grain size in the order of 30 nm. During thermal treatment at 1023 K the microstructure of the films changes due to grain growth, leading to well adhering and well orientated films. Closed cavities are created within the film during the growth. The microstructure and morphology of the films are documented by HRSEM, XRD and XRD pole figures. The high quality of the Pt/YSZ interfaces is documented by high-resolution transmission electron microscopy (HRTEM). The platinum films on (100)-orientated YSZ are polycrystalline with large grains whereas the platinum films on (111)-orientated YSZ are single crystalline with a negligible concentration of grain boundaries. Since these platinum films on YSZ(111) are virtually impermeable for oxygen, microstructures on the basis of these epitaxial films may be used as geometrically and microstructurally well defined model-type electrodes for the study of electrochemical processes at the triple phase boundary Pt(O2)/YSZ and on the surface of platinum.
Keywords: Platinum; Zirconia; Texture; Microstructure; Triple phase boundary; NEMCA effect;

A series of sulfonated poly(ether sulfone) (SPES) were prepared by sulfonating poly(ether sulfone) with chlorosulfonic as sulfonating agent and concentrated sulfuric acid as solvent. Tough and ductile SPES membranes were obtained from DMAc solution. The degree of sulfonation (DS) and ion exchange capacity (IEC) were calculated via 1H NMR and titration. Microphase separated structure comprised of hydrophilic ionic clusters and hydrophobic polymer backbone were observed from atomic force microscopy (AFM) phase images. The hydrophilic ionic clusters became continuous to form channels when DS reached 0.50, corresponding to suddenly increase of water uptake. Combining AFM with water uptake analysis, we found SPES system reached a percolation threshold around DS of 0.39. SPES membranes with DS below 0.39 showed good dimensional stability in water, mechanical stability and oxidative stability. Proton conductivities ranged from 10− 4 to 10− 1 S/cm were measured at room temperature in water. SPES membranes exhibited lower methanol permeability than Nafion 112. A highest value of the proton conductivity-to-methanol permeability ratio was obtained for SPES with DS of 0.39. The results showed that SPES was promising for possible use in proton exchange membrane fuel cells, especially in direct methanol fuel cells.
Keywords: Proton exchange membrane; Sulfonation; Poly(ether sulfone); Direct methanol fuel cell;

Two polymeric lithium salts, lithium polyperfluorobutylene-1,4-bis-sulfonylimide (LiPBSI) and lithium polyperfluorohexylene-1,6-bis-sulfonylimide (LiPHSI), with different CF2 backbone lengths were synthesized by a new and easy method. These two polymeric lithium salts were successfully converted, via ion exchange and Li2CO3 treatment, from polymeric potassium salts which were prepared by condensation polymerizations of perfluoroalkylene-bis-sulfonyl fluorides (FSO2C4F8SO2F and FSO2C6F12SO2F) with 15% potassium hexamethyldisilizane in toluene. Both LiPBSI and LiPHSI were characterized by multi-nuclear (1H, 19F, or 13C) NMR, FT-IR, TGA, DSC, GPC, and so on. The ionic conductivity results of solid polymer electrolytes prepared by resulting lithium salts and poly(ethylene oxide) (PEO) showed that LiPBSI/PEO electrolyte had higher ionic conductivity. Furthermore, the lithium ion transference number of both LiPBSI/PEO and LiPHSI/PEO films were close to 0.4, which was twice that of film prepared from commercial lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).
Keywords: Lithium polyperfluorobutylene-1,4-bis-sulfonylimide (LiPBSI); Lithium polyperfluorohexylene-1,6-bis-sulfonylimide (LiPHSI); Polymeric lithium salts; Solid polymer electrolytes; Transference number;

Doping effects of Al on crystal structures and electrical conductivities of LaGa0.9Mg0.1O2.95 perovskite compounds were investigated. As the amount of doping with Al increased, the symmetry of structure changed to the orthorhombic → the rhombohedral → the cubic, which is reportedly favorable for oxide ion conduction, and lattice parameters decreased monotonically. The Al-doped LaGa0.9Mg0.1O2.95 compounds showed mixed (hole and ion) conduction in air and pure oxide ion conduction in low oxygen partial pressure. The oxide ion conductivities decreased with Al contents in spite of the cubic structure formation. The degradation in oxide ion conduction was attributable to narrowed oxide ion conduction paths in Al-doped structures.
Keywords: Lanthanum Gallate; Perovskite; Oxide ion conductor; Crystal structure; Tolerance factor; Free volume; Al doping;

Low-temperature densification and grain growth of Bi2O3-doped-ceria gadolinia ceramics by Vanesa Gil; Carlos Moure; Pedro Durán; Jesus Tartaj (359-365).
The effect of small amounts (≤ 2.0 wt.%) of Bi2O3 on the sintering characteristics and grain growth of cerium oxide doped with gadolinium oxide has been evaluated. The temperature of the shrinkage-rate maximum decreased by almost 300 °C in the case of the doped gadolinia-modified ceria, (GDC) containing 2.0 wt.% Bi2O3. An apparent density > 99% of the theoretical density (D th) has been achieved on sintering at 1400 °C for 4 h for GDC containing 1.0 wt.% Bi2O3 and of the order of 97.9% on sintering for 2 h for GDC containing 0.5 wt.% Bi2O3. The grain growth kinetics have been studied in terms of the kinetic grain growth equation: D n  =  K o t exp (−Q/RT) for sintering in air from 1400° to 1550 °C. The apparent activation energy for the grain growth of GDC increased to about 892 KJ/mol from 518 KJ/mol for undoped-GDC. This result may indicate that additions of Bi2O3 retard the grain growth of GDC ceramics. The conductivity of 1 wt.% doped samples has been measured by complex impedance spectroscopy (CIS). Doping with Bi2O3 does not modify the conductivity of the GDC solid solution.
Keywords: Doped-ceria; Bismuth oxide; Densification; Grain growth kinetics;

Structural stability and ion conductivity of the Dy and W substituted La2Mo2O9 by Tsu-Yung Jin; M.V. Madhava Rao; Chia-Liang Cheng; Dah-Shyang Tsai; Ming-Hao Hung (367-374).
The structural stability and ion conductivity of (La1.8Dy0.2)(Mo2−x W x )O9 are studied using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy. The structural stabilization effect of W is demonstrated by comparing the microstructures and the oxidation states of ions of as-sintered and H2-reduced samples. Without tungsten, the H2-reduced surface of (La1.8Dy0.2)Mo2O9 is engraved with deep notches at grain boundaries and shallow cuts in the grain interior. At a sufficient W level, the H2-reduced surface is similar to the surface without H2 reduction. The XPS analysis concludes that 20% Mo on the (La1.8Dy0.2)Mo2O9 surface is reduced to Mo4+ and Mo0, whilst all Mo is detected at the oxidation state of + 6 in (La1.8Dy0.2)(Mo1W1)O9 after 600 °C 3%H2 reduction. No α–β phase transformation is experienced in any specimens of (La1.8Dy0.2)(Mo2−x W x )O9, when heated from 300 to 800 °C. The room-temperature lattice parameter of β-phase increases with increasing W content, reaches a maximum at x  = 1.0, then decreases. Considering the W structural stabilization effect, its unfavorable influence on conductivity is tolerable because the sample of (La1.8Dy0.2)(Mo1W1)O9 exhibits a conductivity of 0.18 S cm− 1 at 800 °C, still higher than 0.08 S cm− 1 of La2Mo2O9. The temperature dependence of ion conductivity in this doubly substituted LAMOX is correlated to the Arrhenius form from 350 to 450 °C and the Vogel–Tamman–Fulcher form from 450 to 800 °C, and discussed.
Keywords: Oxygen ion conductor; Conductivity; Mo; Hydrogen reduction; Dy; W;

The xLi2O–(1 −  x)(yB2O3–(1 −  y)P2O5) glasses system is one of the parent compositions for chemically and electrochemically stable solid state electrolyte applicable to thin film battery. The purpose of this study was to seek an optimum composition maximizing the ionic conductivity for the deposition of thin film electrolytes. xLi2O–(1 −  x)(yB2O3–(1 −  y)P2O5) glasses were prepared with wide range of composition, i.e. x  = 0.40–0.47 and B2O3/(B2O3  + P2O5) ratio was 0.17–0.67 (y  = xx ∼ xx). The structural variation of the oxide Li2O–B2O3–P2O5 system was investigated by Raman spectroscopy to find out the correlation with the electrical conductivity. It was shown that under 40 mol% of Li2O the ionic conductivity monotonically increased with increasing of B2O3, while over the 40 mol% of Li2O it exhibited a maximum at a specific B2O3/(B2O3  + P2O5) ratio, typically ∼ 0.5. The structural investigation indicated that the variation in conductivity was closely correlated to the variation of 4-coordinated boron groups.
Keywords: Solid state electrolyte; Glass electrolyte; Conductivity;

Structural, chemical and electrochemical analyses of Cu x V2O5 bronzes thin films by E.A. Souza; A. Lourenço; A. Gorenstein (381-385).
Vanadium pentoxide is one of the most attractive cathodic materials for use in microbatteries. However, the continuous insertion and extraction of lithium ions generate gradative losses in its intercalation capacity during the charge and discharge cycles. The insertion of metallic ions in the oxide matrix, forming bronzes of general formula Me x V2O5 is an alternative to increase the electrochemical performance of V2O5. In this work, vanadium oxides and bronzes, in thin film form, were deposited by means of co-sputtering. Structural, chemical and electrochemical characterizations were realized in order to identify the cristallinity, composition, density and oxidation states of the elements in the film. The electrochemical techniques were used for analysis of the reversibility, charge capacity and determination of the diffusion coefficient for lithium ions. The main conclusion is that the addition of copper increased the specific volumetric capacity of the thin films and a better performance was attained during the charge/discharge cycles.
Keywords: Bronzes; Vanadium oxide; Sputtering; Cathodes; Lithium microbatteries;

Study on the silicon doped lithium trivanadate as cathode material for rechargeable lithium batteries by Ming Zhao; Lifang Jiao; Huatang Yuan; Yan Feng; Ming Zhang (387-391).
Silicon doped lithium trivanadate LiSi x V3O8 (x  = 0.000, 0.025, 0.050, 0.075, 0.100) were prepared via a solid state reaction and then aqueous redox reactions. The compositions, structures and electrochemical properties of the materials were intensively characterized by inductive coupled plasma atomic emission spectroscopy (ICP-AES), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and galvanostatic charge–discharge cycle tests. The results show there are many advantages of the synthetic and modification method in this work such as simple elemental composition control. The structures of silicon doped samples behave readily for lithium transfer and intercalating/de-intercalating. The outstanding performances of the materials benefit from silicon doping significantly. LiSi0.050V3O8 showed the best characteristics among the as-prepared materials. The specific discharge capacity of LiSi0.050V3O8 remained 224.3 mAh·g− 1 at cycle 150 and 143.0 mAh·g− 1 at cycle 300 at a current density of 150 mA·g− 1 in the voltage range of 1.8–4.0 V.
Keywords: LiSi x V3O8; LiV3O8; Cathode material; Lithium batteries;

Power and temperature controlled microwave synthesis of SVO by Catia Arbizzani; Sabina Beninati; Libero Damen; Marina Mastragostino (393-398).
Microwave (MW) synthesis is gaining even more importance also in the field of inorganic materials for the advantageous rapidity and energy efficiency of the process. Although in the exploratory phase of the MW-syntheses acceptable reproducibility may be attained by using low-cost domestic ovens, really controlled synthesis conditions can be achieved only with scientific microwave systems with the control of MW irradiation power and temperature of the sample. In the present paper we describe the synthesis of Ag2V4O11 (SVO), starting from V2O5 and Ag2CO3, by using a commercial single-mode MW oven with an automated power control based on temperature feedback. The resulting material, that was structurally and morphologically characterized, displayed very good performance, comparable to the conventional thermally synthesized SVO, when electrochemically tested in battery configuration in view of its use as cathode material in primary lithium batteries for implantable cardioverter/defibrillators (ICDs).
Keywords: Cathode materials; Implantable cardioverter defibrillator; Lithium batteries; Microwave synthesis; Silver vanadium oxide;

Study on pyrolysing behavior of NiO–SDC composite particles prepared by spray pyrolysis technique by Hiroyuki Yoshida; Hiroshi Deguchi; Mitsunobu Kawano; Kouji Hashino; Toru Inagaki; Hiroshi Ijichi; Masaki Horiuchi; Koichi Kawahara; Seiichi Suda (399-405).
The NiO–samaria doped ceria (SDC) composite powders were prepared by spray pyrolysis technique at temperatures between 400 and 1000 °C. The variation of the particle structure was investigated by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), scanning electron microscope (SEM), and transmission electron microscope (TEM)–energy-dispersive X-ray spectroscopy (EDS). The thermal analysis of raw materials was also carried out. The following facts became clear in this study. Ceria and nickel have been already separated at 400 °C. Samaria is amorphous phase below 600 °C, and is dissolved in ceria at 600 °C or higher. Samaria is distributed uniformly inside the particles before dissolving in ceria. The thermal decomposition temperatures of metal nitrate are: cerium < nickel < samarium. The results of these analyses were explained without contradiction. It was found that it is important to optimize the state of liquid drop before thermal decomposition in order to control the microstructure with this type of particle.
Keywords: Spray pyrolysis; Ni–SDC; XAFS; TEM; Solid oxide fuel cell;

Electrochemical performance of LSCF based thin film cathodes prepared by spray pyrolysis by Daniel Beckel; Ulrich P. Muecke; Thomas Gyger; Guillaume Florey; Anna Infortuna; Ludwig J. Gauckler (407-415).
La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) based thin film cathodes were fabricated by spray pyrolysis and their performance was evaluated with area specific resistance (ASR). With a maximum processing temperature of 650 °C, these cathodes are suitable for application in micro-solid oxide fuel cells (μ-SOFC). The ∼ 500 nm thick cathodes showed performance similar to traditional thick film LSCF cathodes (10–100 μm). However, by using a new material composition Ba0.25La0.25Sr0.5Co0.8Fe0.2O3 −  δ (BLSCF) or by modifying the microstructure, a significant improvement in performance was achieved. Reducing the grain size or introducing a thin dense cathode layer between the porous cathode and the electrolyte were beneficial modifications of the microstructure.
Keywords: Thin film; LSCF; Cathode; Spray pyrolysis; Perovskite;

Electrical and thermal properties of (Ba0.5Sr0.5) 1−x Sm x Co0.8Fe0.2O 3−δ perovskite oxides by Shuyan Li; Zhe Lü; Xiqiang Huang; Bo Wei; Wenhui Su (417-422).
(Ba0.5Sr0.5) 1−x Sm x Co0.8Fe0.2O 3−δ (BSSCF; 0.05≤  x  ≤0.20) compounds were synthesized and characterized by powder X-ray diffraction (XRD), thermogravimetric (TG), electrical conductivity, and thermal expansion coefficient (TEC) measurements. An emphasis is made on the effect of Sm-doping on the material's properties. XRD measurements showed that the BSSCF sample had a cubic perovskite structure, while TG measurements proved the loss of lattice oxygen during heating up. The electrical conductivity increased with temperature up to about 350–450 °C, and then decreased due to the loss of lattice oxygen. Additionally, the lattice oxygen loss caused the differences in electrical conductivity on heating up and cooling down. Electrical conductivity relaxation measurements were performed on the x  = 0.10, 0.20 samples at 450, 470, and 500 °C, and showed that the diffusion coefficient decreased with increasing content of Sm. The TEC values of BSSCF were 19.5–20.1 × 10− 6 K− 1 from 30 to 800 °C.
Keywords: 84.60.Dn; 67.40.Pm; 68.35.Ja; 68.60.Dv; Perovskite; Cathode; Conductivity; Thermal expansion coefficient; (Ba0.5Sr0.5) 1−x Sm x Co0.8Fe0.2O 3−δ ;

Manganese based spinel – like ceramics with NTC – type thermistor behaviour by A. Veres; J.G. Noudem; O. Perez; S. Fourrez; G. Bailleul (423-428).
The structural, electrical and magnetic properties of the spinel-type MgGa2 −  x Mn x O4 compounds have been studied. The samples were prepared by standard solid state reaction method and characterized by X-ray diffraction (XRD), temperature dependent resistivity ρ(T) and magnetic M(T) measurements. The XRD patterns reveal a cubic structure (F d-3m , S.G. No. 227) for all the solid solutions, with x values ranging from 0.1 to 1, confirming the spinel-type structure and the good solubility of Mn in MgGa2O4. The material becomes less resistive as the substitution increase. However the ρ(T) remains quasi-linearly dependent, the range of sensitivity being shifted to lower temperatures. The magnetic characterization showed that with an increase in the manganese content all the samples display paramagnetic behaviour in high temperature range, magnetic ions interacting antiferromagnetically at low temperature. The values of the effective magnetic momentum (μ eff) decrease down to about 4 μ B , as the manganese content increases, reflecting the possible shift of the valence of manganese towards Mn4+. This last effect enables us to suppose that carrier concentration may increase by increasing manganese content and thus improving the electrical conduction through the well-known electron “hopping” mechanism, which is believed to act in this kind of materials.The study highlights the possibility of modelling these manganite-type materials for improved properties, intended to negative temperature coefficient (NTC) type thermistor, for high temperature applications.
Keywords: Manganites; Spinel-like ceramics; NTC-type thermistor; Electron hopping;

Iron/wüstite/magnetite/alumina relationships in plasma coated steel: A TEM study by S. Valette; G. Trolliard; A. Denoirjean; P. Lefort (429-437).
Despite very low surface roughness values of steel substrates (Ra = 0.06 μm), plasma sprayed coatings of Al2O3 exhibited an excellent adhesion (> 60 MPa) when the substrate was preliminary oxidized before coating.Investigation in the interfacial zone, mainly by TEM study, showed a crystallographic continuity through the different heterophase interfaces present from the inner steel substrate up to the outer alumina coating: steel/iron (α-Fe)/wüstite (Fe1−x O)/magnetite (Fe3O4)/metastable alumina (γ-Al2O3).No chemical reaction occurred between iron oxides and alumina, but strong crystallographic relationships linked every phase through the different interfaces.Such a structural continuity explained the solidity of this alloy/ceramic bonding.
Keywords: Transmission Electron Microscopy; Plasma spraying; Alumina coating; Iron oxides; Steel; Adhesion;

Polymethylmethacrylate (PMMA) based polymer gel electrolytes containing ammonium hexafluorophosphate (NH4PF6) show conductivity higher than the corresponding liquid electrolytes. Nanodispersed gels prepared by the dispersion of fumed silica with particle size in the nanometer range to polymer gel electrolytes show conductivity of the order of 10− 2 S/cm at 25 °C. Two maxima observed at very low concentrations, in the variation of conductivity with the concentration of fumed silica, are related to an increase in free ion concentration due to the dissociation of ion aggregates which is also supported by FTIR results, and the formation of a high conducting interfacial layer between the particles of fumed silica and polymer gel electrolytes respectively. The thermal stability of polymer gel electrolytes shows an improvement with the addition of fumed silica and nanodispersed gels have been found to be thermally stable up to 125 °C. The conductivity of nanodispersed gels does not change much over the 20–100 °C temperature range and also remains constant with time.
Keywords: Polymer gel electrolytes; Conductivity; Viscosity; Nanodispersed gels; FTIR; DSC/TGA;

Cation tracer diffusion in the thermoelectric materials Cu3Mo6Se8 and “β-Zn4Sb3 by Eric Chalfin; Hongxia Lu; Rüdiger Dieckmann (447-456).
The diffusion of radioactive tracers, Ag-110m diffusing in Cu3Mo6Se8 and Zn-65 diffusing in “β-Zn4Sb3”, was experimentally studied. Tracer concentration profiles were generated by diffusion-annealing samples in argon atmospheres containing 1–2% H2. The corresponding residual radioactivity profiles were measured and analyzed to determine tracer diffusion coefficients of Ag-110m diffusing in Cu3Mo6Se8 and of Zn-65 diffusing in “β-Zn4Sb3”. The temperatures investigated were between about 195 and 900 °C for Cu3Mo6Se8 and between about 195 and 475 °C for “β-Zn4Sb3”. It was found that the diffusion of Ag in Cu3Mo6Se8 and of Zn in “β-Zn4Sb3” is very fast, with tracer diffusion coefficients on the order of 10− 5 to 10− 6 cm2/s in the temperature ranges considered. The temperature dependencies of the tracer diffusion coefficients denoted above can be described by using Arrhenius-type relations. The values determined for activation energies are 18.70 ± 0.95 kJ/mol for the tracer diffusion of Ag-110m in Cu3Mo6Se8 and 11.07 ± 0.95 kJ/mol for the tracer diffusion of Zn-65 in “β-Zn4Sb3”. These values are comparable to the very low activation energy of 9.16 kJ/mol observed for the diffusion of Ag in the fast ion conductor α-Agl.
Keywords: Thermoelectric materials; Cu3Mo6Se8; β-Zn4Sb3; Tracer diffusion;

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