Carbon dioxide sensing properties of bismuth cobaltite

Bismuth cobaltite with sillenite-type structure was prepared from Co(OH)2 and Bi(NO3)3·6H2O through solid state reaction at 600 °C. Neutron powder diffraction (NPD) data and X-ray absorption spectroscopy revealed the existence of mixed oxidation states for cobalt in this compound, the chemical formula being Bi 12(Bi0.55Co0.45)O19.6. The gas sensing properties of Bi12(Bi0.55Co0.45)O 19.6 were characterized by alternating current, at 200, 300 and 400 °C. The optimal response was observed at 400 °C, using a frequency of 100 kHz. © 2011 Elsevier B.V

In situ neutron diffraction study of the nickel oxihydroxide electrode upon discharge

The redox discharge process of the nickel oxihydroxide electrode (NOE) were followed by in situ neutron diffraction with the aim of getting a deeper insight into the phases and mechanisms involved, paying special attention to the second plateau. A set of deuterated samples was prepared to be used as a reference for the interpretation of the in situ patterns. Neutron diffraction experiments indicate that redox process is the same over both the first and second plateaus and corresponds to a phase transformation over the main part of the oxidation/reduction range and hence indicates that this phenomenon should not be associated to a structural transformation. © 2004 Elsevier B.V. All rights reserved

Synthesis, Short-Range Structure, and Electrochemical Properties of New Phases in the Li-Mn-N-O System

International audienceA crystal-chemical exploration of part of the Li-Mn-N-O system was carried out. Several samples were synthesized using Li3N, MnxN and Li2O and characterized with chemical analysis, XRD, XAS, and NMR. An increase in the starting proportion of Li2O increases the amounts of lithium and oxygen in the compounds, but, according to the XANES Mn K-edge spectra, all the oxynitrides still contain Mn5+ ions preferentially coordinated by N3-, forming [MnN4] tetrahedra. The analysis of the position of these samples in the compositional Li3N-Li2O-MnN, ternary phase diagram and the plot of their cell parameters against the oxygen molar fraction indicates that all the oxynitrides belong to the same tieline, which also includes Li2O but not Li7MnN4. Although the XRD patterns suggest that these samples crystallize in a disordered antifluorite-type structure, the analysis of the Li-6 NMR data indicates that short-range ordering does exist. The performance as electrode materials in lithium batteries of the synthesized samples was also evaluated. Li7.9MnN3.2O1.6 was shown to be the most attractive candidate because of its higher capacity values and improved retention upon cycling with respect to the other members of the series

In situ neutron powder diffraction of a nickel hydroxide electrode

The redox processes occurring at the nickel oxyhydroxide electrodes were followed by in situ neutron diffraction. The aim was to get a deeper insight into the existing phases and the reactivity mechanisms involved in the reduction process, paying special attention to the so-called "second plateau" phenomenon, occasionally appearing during electrochemical reduction at a potential of 0.8 V vs Hg/HgO. Chemically prepared protonated or deuterated nickel hydroxides, having different phase compositions, oxidation state, and particle size were studied to serve as reference samples. The electrochemically driven structural evolution of four samples upon discharge and charge was followed by in situ neutron powder diffraction using a specially designed cell. For both γ and β-NiOOH phases, the neutron diffraction results evidenced a direct and continuous structural transformation into the β-Ni(OH)2 phase upon reduction, on both the first and the second plateau, with no discontinuity when encountering the second plateau. This confirms that the second plateau phenomenon is not due to any intrinsic structural properties of the active material but is related to its surface properties being prone to be strongly dependent upon the electrode preparation

Sol-Gel Synthesis of the Lithium-Ion Conducting Perovskite La0.57Li0.3TiO3. Effect of Synthesis and Thermal Treatments on the Structure and Conducting Properties

Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996.The lithium ionic conducting perovskite La0.57Li0.3TiO3 has been synthesised via a sol-gel method at a temperature of 700 °C. The crystallinity of the product can be greatly increased by further heat treatment at 1000 °C. In this paper the product of the sol-gel synthesis is compared with the product of conventional solid-state synthesis, and the influence of the synthesis method as well as of quenching on the crystal structure and ionic conductivity has been studied. AC-impedance measurements show two contributions to the ionic conductivity, which can be adscribed to intergranular and intragranular effects, respectively. A lower intergranular resistivity is observed for sol-gel samples, while quenching mainly affects the materials prepared by solid-state reaction. The crystal structure of the material prepared by the sol-gel method is identical to that of the material prepared by the solid state reaction, although the synthesis temperature is nearly 600 °C lower. A tetragonal superstructure is observed when either type of material is slowly cooled from 1300 °C. Quenching from the same temperature results in the suppression of that superstructure.The authors wish to thank the European Union for financial support of this work by the European Haman Capital and Mobility Program (CHRX-CT94-588), as well as funds from DGIGYT (Spain, PB93-0122).Peer reviewe

On the origin of the second low-voltage plateau in secondary alkaline batteries with nickel hydroxide positive electrodes

The nickel oxyhydroxide electrode (NOE) that acts as the positive electrode in Ni-based rechargeable alkaline batteries was studied. A survey of the influence of crystal-chemistry factors (nature and ratio of the various nickel hydroxide phases), cycling parameters (charge/discharge rates, charge/discharge cutoff voltages, and percentage of overcharge), and technological parameters (nature of the current collector, active material morphology, and type of additives) on the appearance of the second voltage plateau was performed. Direct experimental evidence shows that the appearance of the second plateau is directly linked to the amount of the γ-phase present in the nickel oxyhydroxide electrode prior to its discharge. The occasional appearance of this phase in the electrode results from a poor active material/current collector interface related to the electrode-forming technology, or to secondary reactions that can lead to a physical disconnection of the active material upon cycling. Based on these findings, the presence of this γ-phase accounts for the ohmic drop that has led to previous speculation of a barrier layer as the origin of the second plateau. Finally, tentative recommendations to eliminate or mitigate the appearance of the second plateau phenomena are given

On the role of defects in decreasing the extra 3.3/3.95 and 4.5 V redox steps in Li-Mn-O spinels

LiMn2O4 spinels were studied with the aim of assessing the role of different types and amounts of defects in blocking the phase transition from spinel to double hexagonal that is associated with anomalous 4.5 and 3.3/3.95 V redox steps. The influence of the type of MnO2 precursor (β or γ, both with diverse amounts of stacking faults), the effect of introducing defects in the final spinel by ball milling or of cationic subsitutions on the spinel 16d sites (Al or Li) were examined. Electrochemical experiments performed on all these defective samples indicate that defects block the phase transition to a certain extent. The introduction of either Li or Al in spinel 16d sites proved to be the most effective to prevent the structural transformation, and thus eliminate the anomalous redox steps that are detrimental to the electrochemical performances of LiMn2O4. © 2001 Elsevier Science B.V

Competition between the two reduction reactions of the γ(111) phase in the ni-based batteries

We show that the γ(III)/β(II) phase transition is at the origin of the second plateau at 0.8V in the Ni-based batteries by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies and intermittent galvanostatic measurements (GITT). This study shows that the equilibrium voltage of this transition is 1.25V vs Cd-Cd(OH) 2, thus implying an overvoltage of 400 mV. Direct evidence for a textural memory effect trough the γ(III)/β(II) phase transition is given by TEM studies. The reoxidation of the β(II) phase to γ(III) phase occurs without going trough the β(III) phase. © 1998 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint

Amino acid transporters expression in acinar cells is changed during acute pancreatitis

Pancreatic acinar cells accumulate amino acids against a marked concentration gradient to synthesize digestive enzymes. Thus, the function of acinar cells depends on amino acid uptake mediated by active transport. Despite the importance of this process, pancreatic amino acid transporter expression and cellular localization is still unclear. We screened mouse pancreas for the expression of genes encoding amino acid transporters. We showed that the most highly expressed transporters, namely sodium dependent SNAT3 (Slc38a3) and SNAT5 (Slc38a5) and sodium independent neutral amino acids transporters LAT1 (Slc7a5) and LAT2 (Slc7a8), are expressed in the basolateral membrane of acinar cells. SNAT3 and SNAT5, LAT1 and LAT2 are expressed in acinar cells. Additional evidence that these transporters are expressed in mature acinar cells was gained using acinar cell culture and acute pancreatitis models. In the acute phase of pancreatic injury, when acinar cell loss occurs, and in an acinar cell culture model, which mimics changes occurring during pancreatitis, SNAT3 and SNAT5 are strongly down-regulated. LAT1 and LAT2 were down-regulated only in the in vitro model. At protein level, SNAT3 and SNAT5 expression was also reduced during pancreatitis. Expression of other amino acid transporters was also modified in both models of pancreatitis. The subset of transporters with differential expression patterns during acute pancreatitis might be involved in the injury/regeneration phases. Further expression, localization and functional studies will follow to better understand changes occurring during acute pancreatitis. These findings provide insight into pancreatic amino acid transport in healthy pancreas and during acute pancreatitis injury