Aspects of electronic transport in YBaCo4O7+δ pellets

YBaCo₄O_7+δ powders were obtained by standard solid state reaction und their structural, morphological and electrical properties carefully analyzed. The X-ray powder diffraction patterns showed reflexes corresponding to a pure hexagonal structure (space group P6₃mc). The lattice parameters resulted to be very close to those reported in the literature for high-quality samples. Raman spectra at room temperature allowed for identifying bands associated with vibrating modes of CoO₄ and Y₂O₆ in tetrahedral and octahedral coordination, respectively. Additional bands, which seemed to stem from CoO in octahedral coordination, were also clearly identified. The dependence of the resistivity on temperature showed a semiconducting-like behavior and no indication of structural phase transition was observed up to temperatures as low as 20 K. The electronic transport mechanism in this material was analyzed within the framework of standard models as thermal activation, polaronic-type conductivity or Mott variable-range hopping. Contrary to some reports in the literature in which thermal activation was reported to be the main transport mechanism, careful analysis of the obtained resistivity data (this work) favored the variable-range hopping conduction model. Certainly, the experimental data recorded in a wide temperature range were well described by the function ρ(T) = ρ₀exp[(T^*/T)^1/4]. The fit procedure yielded a temperature scale T^* ～ 10⁶ K, similar to that found in other transition metal oxides. This parameter, in turn, allowed for estimating the density of states at the Fermi level N(E_F) for this compound.     

Oxygen storage capacity of substituted YBaCo4O7+δ oxygen carriers

Depletion of non-renewable energy sources are at elevated manner due to the rapid growth of industrialization and transportation sector in last few decades and leads to further energy demand. Biodiesels especially second-generation fuels from non-edible oil resources are alternate sources for replacement of diesel fuel in CI engines due to their considerable environmental benefits. In the present work, non-edible feedstock of Calophyllum inophyllum seed oil (tamanu oil) is used for biodiesel production. Transesterification method is used for preparation of biodiesel in the existence of methanol with NaOH as catalyst. The copper nanoparticles are synthesized by electrochemical method, and it is characterized by using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). XRD and SEM results confirm the presence of copper nanoparticle and size of around 30 nm. This paper aims to investigate the effects of the copper additive nanoparticles with biodiesel blends on the engine performance, combustion and emission characteristics of single-cylinder direct-injection diesel engine and compared that with diesel fuel. The results showed that the addition of nano-additives enhances brake thermal efficiency and reduces specific fuel consumption compared to biodiesel blends but slightly lower than diesel. Combustion characteristics also are enhanced by improved oxidation reaction inside the combustion chamber which resulted in higher heat release rate. The emissions of HC, NO_x and O₂ are significantly reduced for nano-additive blends compared to diesel but increased CO₂ emission was observed. It is noticed that higher CO₂ emission and substantial reduction of unused O₂ emissions from engine fueled with nano-additive are evident for enhanced oxidation and better combustion. Energy and exergy analysis of the diesel engine is carried out to estimate the effect of using nanoparticle additive with biodiesel.

     

High-temperature transport and stability of SrFe1−xNbxO3 − δ

The conductivity is measured in the series of solid solutions SrFe_1 ? xNb_xO_3 ? δ, where x = 0.05, 0.1, 0.2, 0.3, 0.4, within the oxygen partial pressure limits 10^?18–0.5 atm and temperature range 650–950 °C. The contributions to the total conductivity from oxygen ions, electrons and electron holes are obtained based on their different pressure dependences. The doped derivative with x = 0.1 is found to be a singular composition where ion conductivity attains a maximal value while activation energy for ion transport is minimal. This peculiar behavior is attributed to formation of favorable microstructure in the oxide. The deeper doping results in deterioration of ion transport, which is explained by oxygen vacancy filling. It is shown that replacement of iron for niobium favors enhanced thermodynamic stability towards reduction. The oxygen permeability is evaluated from the conductivity data, and it achieves rather high values in the doped derivatives. These oxides can, therefore, be recommended for further evaluation as oxygen separating membrane materials for partial oxidation of natural gas.     

Electronic properties of Pr4Ni3O10±δ

Two synthesis methods for preparing Pr₄Ni₃O_10±δ are compared : a modified sol — gel route and a nitrate — citrate one. It is shown that the autoignition involved in the nitrate — citrate route provides good conditions ressembling the Rapid Thermal Annealing procedure. The oxygen stoichiometry of Pr₄Ni₃O_10±δ phases is measured according to the method of synthesis and thermal treatment. The compounds are metallic as seen by electrical resistivity measurements and thermoelectric power. We show that the adjustment of δ in this series is an important parameter of the transport properties that change from metallic for −0.1 <δ < 0.1 to insulating for Pr₄Ni₃O_8.25. An electronic anomaly is evidenced at 160 K, which intensity is more marked for the stoichiometric Pr₄Ni₃O₁₀. Our results are consistent with the existence of a charge density wave instability.     

Synthesis and electrochemical properties of regular hexahedron α-Fe2O3

Synthesis of α-Fe₂O₃ compound with regular hexahedron shape is firstly reported. X-ray diffraction and scan electron microscope are used to characterize the structure and morphology of the prepared sample, respectively. The average edge length of hexahedron is about 0.9 μm. A reaction mechanism has been proposed. The pH value is a crucial factor for the formation and shape of α-Fe₂O₃. Moreover, electrochemical impedance spectroscopy and charge-discharge test of α-Fe₂O₃ as anode material in lithium ion batteries are evaluated. The data indicate that the synthesized regular hexahedron α-Fe₂O₃ can show better electrochemical properties than that of the commercial.     

High-temperature electrical conductivity and electrochemical activity in oxygen redox reaction of La-doped Sr2FeCo0.5Mo0.5O6-δ

Journal of Solid State Electrochemistry - High-temperature electrical conductivity and electrochemical activity in the oxygen redox reaction of Sr2FeCo0.5Mo0.5O6-δ (SFCM) and...     

Microstructure and electrochemical properties of porous La2NiO4+δ electrode screen-printed on Ce0.8Sm0.2O1.9 electrolyte

Superfine and uniform La₂NiO_4+δ powder was synthesized by a polyaminocarboxylate complex precursor method. La₂NiO_4+δ layers were screen-printed on dense Ce_0.8Sm_0.2O_1.9 electrolyte substrates and sintered at 900–1,100 °C. The microstructure and electrochemical properties of the resulting porous electrodes were investigated with respect to sintering temperature. The results indicate a significant effect of sintering temperature on the microstructure and electrode polarization. It was found that elevating sintering temperature was favorable to the charge transfer process whereas undesired for the oxygen surface exchange process due to an increase of the grain size. Sintering at 900 °C was determined to be preferred in terms of the polarization resistance of the electrode. The porous electrode sintered at the temperature showed a fine-grained microstructure (about 200 nm) and a relatively low polarization resistance of 0.28 Ω cm² at 800 °C. This work suggests that preparing the electrode from superfine starting powder is contributive to modifying the polarization properties.     

Exploring the electron-hole transport nature and optoelectronic properties of 4-nitro-4′-amino-azobenzene-based dyes

Structural Chemistry - Charge transport and electronic properties of 4-nitro-4′-amino-azobenzene compounds with donor-acceptor backbone were examined at the molecular level. Optical...     

Synthesis and electrochemical properties of nanostructured LiAl x Mn2 − x O4 − y Br y particles

Nanostructured LiAl _x Mn_2 − x O_4 − y Br _y particles were synthesized successfully by annealing the mixed precursors, which were prepared by room-temperature solid-state coordination method using lithium acetate, manganese acetate, lithium bromide, aluminum nitrate, citric acid, and polyethylene glycol 400 as starting materials. X-ray diffractometer patterns indicated that the particles of the as-synthesized samples are well-crystallized pure spinel phase. Transmission electron microscopy images showed that the LiAl _x Mn_2 − x O_4 − y Br _y samples consist of small-sized nanoparticles. The results of galvanostatic cycling tests revealed that the initial discharge capacity of LiAl_0.05Mn_1.95O_3.95Br_0.05 is 119 mAh g⁻¹; after the 100th cycle, its discharge capacity still remains at 92 mAh g⁻¹. The introduction of Al and Br in LiMn₂O₄ bring a synergetic effect and is quite effective in increasing the capacity and elevating cycling performance.     

Comparison of structure and electrochemical properties for 5 V LiNi0.5Mn1.5O4 and LiNi0.4Cr0.2Mn1.4O4 cathode materials

Spinel LiNi_0.5Mn_1.5O₄ and LiMn_1.4Cr_0.2Ni_0.4O₄ cathode materials have been successfully synthesized by the sol–gel method using citric acid as a chelating agent. The structure and electrochemical performance of these as-prepared powders have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and the galvanostatic charge–discharge test in detail. XRD results show that there is a small Li _y Ni_1-y O impurity peak placed close to the (4 0 0) line of the spinel LiNi_0.5Mn_1.5O₄, and LiMn_1.4Cr_0.2Ni_0.4O₄ has high phase purity, and the powders are well crystallized. SEM indicates that LiMn_1.4Cr_0.2Ni_0.4O₄ has a slightly smaller particle size and a more regular morphological structure with narrow size distribution than those of LiNi_0.5Mn_1.5O₄. Galvanostatic charge–discharge testing indicates that the initial discharge capacities of LiMn_1.4Cr_0.2Ni_0.4O₄ and LiNi_0.5Mn_1.5O₄ cycled at 0.15 C are 129.6 and 130.2 mAh g⁻¹, respectively, and the capacity losses compared to the initial value, after 50 cycles, are 2.09% and 5.68%, respectively. LiMn_1.4Cr_0.2Ni_0.4O₄ cathode has a higher electrode coulombic efficiency than that of the LiNi_0.5Mn_1.5O₄ cathode, implying that Ni and Cr dual substitution is beneficial to the reversible intercalation and de-intercalation of Li⁺.     

High-temperature transport properties, thermal expansion and cathodic performance of Ni-substituted LaSr2Mn2O7−δ

The substitution of manganese with nickel in LaSr₂Mn₂O_7−δ, where the solubility limit corresponds to approximately 25% Mn sites, enhances the Ruddlesden-Popper phase stability at elevated temperatures and atmospheric oxygen pressure. The total conductivity of LaSr₂Mn_2−yNi_yO_7−δ (y=0-0.4) decreases with nickel additions, whilst the average thermal expansion coefficients calculated from dilatometric data in the temperature range 300-1370 K increase from (11.4-13.7)×10⁻⁶ K⁻¹ at y=0 up to (12.5-14.4)×10⁻⁶ K⁻¹ at y=0.4. The conductivity and Seebeck coefficient of LaSr₂Mn_1.6Ni_0.4O_7−δ, analyzed in the oxygen partial pressure range 10⁻¹⁵-0.3 atm at 600-1270 K, display that the electronic transport is n-type and occurs via a small polaron mechanism. Reductive decomposition is observed at the oxygen pressures close to Ni/NiO boundary, namely ∼2.3×10⁻¹¹ atm at 1223 K. Within the phase stability domain, the electronic transport properties are essentially p(O₂)-independent. The steady-state oxygen permeability of dense LaSr₂Mn_1.6Ni_0.4O_7−δ membranes is higher than that of (La,Sr)MnO_3−δ, but lower if compared to perovskite-like (Sr,Ce)MnO_3−δ. Porous LaSr₂Mn_1.6Ni_0.4O_7−δ cathodes in contact with apatite-type La₁₀Si₅AlO_26.5 solid electrolyte exhibit, however, a relatively poor electrochemical performance, partly associated with strong cation interdiffusion between the materials.     

Isopiestic Studies of Aqueous MgB4O7 and MgSO4 + MgB4O7 at 298.15 K and Representation with Pitzer’s Ion-Interaction Model

Water activities and stoichiometric osmotic coefficients for the systems MgB₄O₇+H₂O and MgSO₄+MgB₄O₇+H₂O have been measured at 298.15 K by the isopiestic method using a improved isopiestic device; the saturated solution molalities of MgB₄O₇ are very low for these systems. These measurements extended from the near saturated molalities to supersaturation for the MgB₄O₇ binary solutions and from total molalities m _T of 0.1787 to 2.2374 mol?kg^?1 with seven MgB₄O₇ molality fractions from 0.005 to 0.095 for the ternary solutions, respectively. The water activities of MgSO₄ binary solutions (Y _B = 0.0) were obtained by extrapolation of the present experimental results and were in agreement with the data from Rard and Miller (J. Chem. Eng. Data 26:33–38, 1981). The experimental stoichiometric osmotic coefficients are represented using Pitzer’s ion-interaction model with a modified value of α _B2=7.59 kg^1/2?mol^?1/2 in the term, $B_{\mathrm{Mg,B}_{4}\mathrm{O}_{7}}^{\phi}$ . Two sets of ion-interaction model parameters are presented for MgSO₄+MgB₄O₇+H₂O. The mixing parameters of the first set were evaluated using the presently calculated MgB₄O₇ single-salt parameters obtained from its binary-solution data. All the parameters relative to borate in the second set were estimated simultaneously from all the measured stoichiometric osmotic coefficient data for binary and ternary solutions in the present work, and were obtained with standard deviations of 0.0022 for MgB₄O₇ single salt-parameters and 0.0063 for the mixing parameters. The MgSO₄ single-salt parameters reported by Rard and Miller (J. Chem. Eng. Data 26:33–38, 1981) were used for the evaluation of both sets of the ion-interaction parameters. The stoichiometric mean activity coefficients of the solutes for the systems are primarily calculated using Pitzer’s standard equations for the activity coefficient with the same values of parameters and the exponential coefficients of α ₁, α ₂ and α _B2 for the osmotic coefficient model. The effects of the ionic interactions on the thermodynamic properties for the studied systems are discussed.     

High-temperature electron-hole transport in PrBaCo2O5+δ

The oxygen content, conductivity and thermopower in the double perovskite-like cobaltite PrBaCo₂O_5+δ are reported in the oxygen partial pressure range 2×10⁻⁶-0.21 atm and temperatures between 650 and 950 °C. The electrical properties are shown to be continuous through the transition from δ>0.5 to δ<0.5. The variations of transport parameters with temperature and oxygen content reveal hole polaron hopping conduction within oxygen non-stoichiometry domain δ<0.5.     

Thermodynamic properties and electrochemical behavior of lithium–germanium alloys

Published data on the phase diagram of the lithium–germanium system, on the thermodynamic properties of Li–Ge alloys, on their electrochemical behavior in various media, and on prospects for using them in lithium–ion batteries and in other chemical current sources are analyzed.     

Photophysical and electrochemical properties of π-extended molecular 2,1,3-benzothiadiazoles

The reaction of 4,7-dibromo-2,1,3-benzothiadiazole with arylboronic acids (phenyl, 1-naphthyl, 4-methoxyphenyl, 4-chlorophenyl and 4-trifluoromethylphenyl) in the presence of catalytic amounts of a NCP-pincer palladacycle affords photoluminescent π-extended 4,7-diaryl-2,1,3-benzothiadiazoles 4a-e in high yields. These 4,7-diaryl-2,1,3-benzothiadiazoles exhibit high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-bis-naphthyl-2,1,3-benzothiadiazole 4b presents two different lifetimes (bi-exponential decay) due to the presence of two atropisomers. The Sonogashira coupling reaction of 4,7-diethynyl-2,1,3-benzothiadiazole 6 with the corresponding halo-aryl compounds (iodobenzene, 1-bromonaphthalene, 4-iodoanisole, 4-bromo-N,N-dimethylaniline and 2-bromopyridine) afforded the photoluminescent π-extended 4,7-bis-alkynylaryl-2,1,3-benzothiadiazoles 7a-e, also in high yields. These 4,7-diethynyl-2,1,3-benzothiadiazoles also present high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-disubstituted-2,1,3-benzothiadiazoles 4a-e and 7a-e exhibit different electrochemical behavior. The presence of two ethynyl spacers in 2,1,3-benzothiadiazoles 7a-e shifts the reduction potentials to less cathodic values and also results in two well-defined and distinct reduction processes.     

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC₄H₉)₄, LiCH₃COO·2H₂O, and La(NO₃)₃·6H₂O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li₄Ti₅O₁₂ is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La³⁺ does not affect the structure of Li₄Ti₅O₁₂, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li₄Ti₅O₁₂ presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li₄Ti₅O₁₂ exhibits excellent reversible capacities of 156.16 and 150.79 mAh?g^?1, respectively. The excellent rate capability and good cycling performance make La-doped Li₄Ti₅O₁₂ a promising anode material for lithium-ion batteries in energy storage systems.     

Compilation of all the isothermal mass/charge transport properties of the mixed conducting La2NiO(4+δ) at elevated temperatures

It is known [H.-S. Kim and H.-I. Yoo, Phys. Chem. Chem. Phys., DOI:10.1039/c0cp00722f] that all the isothermal mass and charge transport properties of a mixed ionic electronic conductor compound can be universally represented by a 2 × 2 Onsager transport coefficient matrix. Furthermore, the three independent coefficients of the matrix can be determined from a simple relaxation experiment under the ion-blocking condition in association with the equation of state with respect to the nonstoichiometry or thermodynamic factor. By using this method, we compile the transport matrices at 800 °C, 900 °C and 1000 °C, respectively, on the system of La(2)NiO(4+δ) across its entire stability range, and calculate thereby its transport properties to compare with the literature values available. The interference effect between mobile oxygen ions and holes upon their transfer is discussed.     

Oxygen transport and thermomechanical properties of SrFe(Al)O3-δ –SrAl2O4 composites: microstructural effects

Measurements of oxygen permeation through dense composite membranes showed a considerable influence of processing conditions on the surface exchange kinetics, while the bulk ambipolar conductivity is almost unaffected by microstructural factors. Compared to the materials prepared via the glycine–nitrate process (GNP), the surface limitations to oxygen transport are significantly higher for dual-phase made of a commercial powder synthesized by spray pyrolysis. This difference in behavior may be related to compositional inhomogeneities in the grains of A-site deficient perovskite phase and an enhanced surface concentration of grain boundaries in the case of GNP-synthesized composite, which has also smaller grain size, slightly higher thermal expansion and lower total conductivity. No essential effects on Vickers hardness, varying in the range 6.3–6.5 GPa, were found. The deposition of porous catalyst layers onto the composite surface exposed to reducing environment leads to membrane decomposition. For the fabrication of tubular membranes, the cold isostatic pressing technique was, hence, combined with mechanical treatment to increase the specific surface area without incorporation of catalytically active components.