The oxygen nonstoichiometry,defect structure,and thermodynamic characteristics of disordering of nickel-and iron-substituted lanthanum cobaltites

The oxygen nonstoichiometry of nickel-and iron-substituted lanthanum cobaltites of the compositions LaCo_1?x Ni _x O_3?δ (x = 0.1, 0.3) and LaCo_0.9Fe_0.1O_3?δ was studied by high-temperature thermogravimetric analysis over the temperature and oxygen partial pressure ranges 1223–1473 K and 10^?3–0.21 atm. The partial replacement of cobalt with nickel (an acceptor impurity) in lanthanum cobaltite was found to increase the number of defects in the oxygen sublattice, whereas the replacement with iron (a donor impurity) decreased this number. Correlations between the experimental \(\log p_{O_2 } = f(\delta )\) dependences and the suggested models of formation of point defects were analyzed taking into account the formation of Schottky defects. Interrelation between the defect structure, partial molar thermodynamic characteristics of oxygen release from the crystal lattices of the oxides studied, and the nature of substituting impurities (Ni and Fe) in lanthanum cobaltite was demonstrated.     

Reversible Entropy-Driven Defect Migration and Insulator-Metal Transition Suppression in VO2 Nanostructures for Phase-Change Electronic Switching

Oxygen defects are among essential issues and required to be manipulated in correlated electronic oxides with insulator-metal transition (IMT). Besides, surface and interface control are necessary but challenging in field-induced electronic switching towards advanced IMT-triggered transistors and optical modulators. Herein, we demonstrated reversible entropy-driven oxygen defect migrations and reversible IMT suppression in vanadium dioxide (VO₂) phase-change electronic switching. The initial IMT was suppressed with oxygen defects, which is caused by the entropy change during reversed surface oxygen ionosorption on the VO₂ nanostructures. This IMT suppression is reversible and reverts when the adsorbed oxygen extracts electrons from the surface and heals defects again. The reversible IMT suppression observed in the VO₂ nanobeam with M2 phase is accompanied by large variations in the IMT temperature. We also achieved irreversible and stable IMT by exploiting an Al₂O₃ partition layer prepared by atomic layer deposition (ALD) to disrupt the entropy-driven defect migration. We expected that such reversible modulations would be helpful for understanding the origin of surface-driven IMT in correlated vanadium oxides, and constructing functional phase-change electronic and optical devices.     

Synthesis of Nanoporous Ni‐Co Mixed Oxides by Thermal Decomposition of Metal‐Cyanide Coordination Polymers

A straightforward strategy to prepare nanoporous metal oxides with well‐defined shapes is highly desirable. Through thermal treatment and a proper selection of metal‐cyanide coordination polymers, nanoporous nickel‐cobalt mixed oxides with different shapes (i.e., flakes and cubes) can be easily prepared. Our nanoporous materials demonstrate high electrocatalytic activity for oxygen evolution reaction.     

Méthode de dosage du nickel métallique en présence de composés oxydés de nickel dans des matières complexes (minerals)

During investigations on the behaviour of metallic nickel in HgCl₂-, KCN- and HCl-containing media, it was noticed in certain cases that nickel metal dissolution was achieved, while a mixture of nickel oxides remained absolutely unaltered.The working conditions were determined, and on the basis of the results obtained two methods have been developed for the determination of metallic nickel in the presence of nickel oxides in complex materials, including ores.These methods are described, in detail and the results of the experiments are given: they show that an accuracy of about 5 % can be obtained.     

Transition Metal Oxides for the Oxygen Reduction Reaction: Influence of the Oxidation States of the Metal and its Position on the Periodic Table

Electrocatalysts have been developed to meet the needs and requirements of renewable energy applications. Metal oxides have been well explored and are promising for this purpose, however, many reports focus on only one or a few metal oxides at once. Herein, thirty metal oxides, which were either commercially available or synthesized by a simple and scalable method, were screened for comparison with regards to their electrocatalytic activity towards the oxygen reduction reaction (ORR). We show that although manganese, iron, cobalt, and nickel oxides generally displayed the ability to enhance the kinetics of oxygen reduction under alkaline conditions compared with bare glassy carbon, there is no significant correlation between the position of a metal on the periodic table and the electrocatalytic performance of its respective metal oxides. Moreover, it was also observed that mixed valent (+2, +3) oxides performed the poorest, compared with their respective pure metal oxides. These findings may be of paramount importance in the field of renewable energy.     

A Memristive Element Based on an Electrically Controlled Single‐Molecule Reaction

The exponential proliferation of data during the information age has required the continuous exploration of novel storage paradigms, materials, and devices with increasing data density. As a step toward the ultimate limits in data density, the development of an electrically controllable single‐molecule memristive element is reported. In this device, digital information is encoded through switching between two isomer states by applying a voltage signal to the molecular junction, and the information is read out by monitoring the electrical conductance of each isomer. The two states are cycled using an electrically controllable local‐heating mechanism for the forward reaction and catalyzed by a single charge‐transfer process for the reverse switching. This single‐molecule device can be modulated in situ, is fully reversible, and does not display stochastic switching. The I–V curves of this single‐molecule system also exhibit memristive character. These features suggest a new approach for the development of molecular switching systems and storage‐class memories.     

Ordered mesoporous alumina-supported metal oxides

The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.     

Lan+1NinO3n+1(n=1～4)复合氧化物的制备、表征和催化性能的研究

合成了(AO)(ABO3)n(A=La, B=Ni, n-1～4)型系列复合氧化物。用XRD, XPS,IR, TPD, TPR等方法对其进行了表征, 研究了结构特征, 氧化-还原性能。用化学分析方法测定了镍的价态及氧缺陷, 考察了该系列复合氧化物对CO, CH4的完全氧化活性, 并对其活性与化学组成及结构间的关系进行了讨论。     

Oxygen Isotope Labeling Experiments Reveal Different Reaction Sites for the Oxygen Evolution Reaction on Nickel and Nickel Iron Oxides

Nickel iron oxide is considered a benchmark nonprecious catalyst for the oxygen evolution reaction (OER). However, the nature of the active site in nickel iron oxide is heavily debated. Here we report direct spectroscopic evidence for the different active sites in Fe‐free and Fe‐containing Ni oxides. Ultrathin layered double hydroxides (LDHs) were used as defined samples of metal oxide catalysts, and ¹⁸O‐labeling experiments in combination with in situ Raman spectroscopy were employed to probe the role of lattice oxygen as well as an active oxygen species, NiOO^?, in the catalysts. Our data show that lattice oxygen is involved in the OER for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. Moreover, NiOO^? is a precursor to oxygen for Ni and NiCo LDHs, but not for NiFe and NiCoFe LDHs. These data indicate that bulk Ni sites in Ni and NiCo oxides are active and evolve oxygen via a NiOO^? precursor. Fe incorporation not only dramatically increases the activity, but also changes the nature of the active sites.     

Spatial nonuniformity in resistive-switching memory effects of NiO

Electrically driven resistance change phenomenon in metal/NiO/metal junctions, so-called resistive switching (RS), is a candidate for next-generation universal nonvolatile memories. However, the knowledge as to RS mechanisms is unfortunately far from comprehensive, especially the spatial switching location, which is crucial information to design reliable devices. In this communication, we demonstrate the identification of the spatial switching location of bipolar RS by introducing asymmetrically passivated planar NiO nanowire junctions. We have successfully identified that the bipolar RS in NiO occurs near the cathode rather than the anode. This trend can be interpreted in terms of an electrochemical redox model based on ion migration and p-type conduction.     

Oxygen Vacancy Diffusion and Condensation in Lithium‐Ion Battery Cathode Materials

Oxygen vacancies (OV) are native defects in transition metal (TM) oxides and their presence has a critical effect on the physicochemical properties of the oxide. Metal oxides are commonly used in lithium‐ion battery (LIB) cathodes and there is still a lack of understanding of the role of OVs in LIB research field. Here, we report on the behavior of OVs in a single‐crystal LIB cathode during the non‐equilibrium states of charge and discharge. We found that microcrack evolution in a single crystal occurs due to OV condensation in specific crystallographic orientations generated by the continuous migration of OVs and TM ions. Moreover, understanding the effects of the presence and diffusion of OVs in metal oxides enables the elucidation of most of the conventional mechanisms of capacity fading in LIBs and provides new insights for new electrochemical applications.     

Pentacoordinate Ni(II) complexes: preparation, magnetic measurements, and ab initio calculations of the magnetic anisotropy terms

Two novel mononuclear five-coordinate nickel complexes with distorted square-pyramidal geometries are presented. They result from association of a tridentate "half-unit" ligand and 6,6'-dimethyl-2,2'-bipyridine according to a stepwise process that highlights the advantage of coordination chemistry in isolating an unstable tridentate ligand by nickel chelation. Their zero-field splittings (ZFS) were studied by means of magnetic data and state-of-the-art ab initio calculations. Good agreement between the experimental and theoretical axial D parameters confirms that large single-ion nickel anisotropies are accessible. The synthetic process can also yield dinuclear nickel complexes in which the nickel ions are hexacoordinate. This possibility is facilitated by the presence of phenoxo oxygen atoms in the tridentate ligand that can introduce a bridge between the two nickel ions. Two different double bridges are characterized, with the bridging oxygen atoms coming from each nickel ion or from the same nickel ion. This coordination change introduces a difference in the antiferromagnetic interaction parameter J. Although the magnetic data confirm the presence of single-ion anisotropies in these complexes, these terms cannot be determined in a straightforward way from experiment due to the mismatch between the principal axes of the local anisotropies and the presence of intersite anisotropies.     

Simple baths for the deposition of nickel oxides

In the present investigation new baths have been adopted for the anodic deposition of different nickel oxides. The deposition of the different oxides was carried out from their metal salt solutions in the presence of a complexing agent. The following oxides were obtained: NiO₂ from nickel chloride in the presence of ammonium chloride and sodium fluoride; Ni₂O₃ from nickel sulphate in the presence of ammonium chloride and citric acid; Ni₃O₄ from nickel chloride in the presence of sodium hydroxide, formaldehyde and potassium chloride, and finally NiO from nickel chloride in the presence of sodium carbonate, sodium chloride and ethanol.     

Study on the variation of morphology and separation behavior of the stainless steel supported membranes at high temperature

Palladium composite membranes were prepared on stainless steel (SUS) supports modified by nickel submicron powder and colloidal silica sols. Permeation tests of the palladium composite membranes were carried out at high temperature in order to observe the thermal stability of the membrane. The palladium composite membrane failed with formation of plenty of pinholes in the presence of hydrogen at high temperature. The failure of the composite membrane was verified by comparing the nitrogen permeance before hydrogen permeation test with that after hydrogen permeation test and comparing the H₂/N₂ selectivity for single gas permeation test with that for mixture gas permeation test. The variation of the membrane surface due to the failure of the membrane was characterized in scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS) analyses. As a result, it can be concluded that reducible metal oxides can be attributed to the failure of the composite membranes resulting from reduction of the metal oxides by hydrogen whichever position in the membrane the metal oxides are layered.     

Origin of Surface Reconstruction in Lattice Oxygen Oxidation Mechanism Based-Transition Metal Oxides: A Spontaneous Chemical Process

A fundamental understanding of surface reconstruction process is pivotal to developing highly efficient lattice oxygen oxidation mechanism (LOM) based electrocatalysts. Traditionally, the surface reconstruction in LOM based metal oxides is believed as an irreversible oxygen redox behavior, due to the much slower rate of OH⁻ refilling than that of oxygen vacancy formation. Here, we found that the surface reconstruction in LOM based metal oxides is a spontaneous chemical reaction process, instead of an electrochemical reaction process. During the chemical process, the lattice oxygen atoms were attacked by adsorbed water molecules, leading to the formation of hydroxide ions (OH⁻). Subsequently, the metal-site soluble atoms leached from the oxygen-deficient surface. This work also suggests that the enhancement of surface hydrophilicity could accelerate the surface reconstruction process. Hence, such a finding could add a new layer for the understanding of surface reconstruction mechanism.     

A Memristive Element Based on an Electrically Controlled Single-Molecule Reaction

The exponential proliferation of data during the information age has required the continuous exploration of novel storage paradigms, materials, and devices with increasing data density. As a step toward the ultimate limits in data density, the development of an electrically controllable single-molecule memristive element is reported. In this device, digital information is encoded through switching between two isomer states by applying a voltage signal to the molecular junction, and the information is read out by monitoring the electrical conductance of each isomer. The two states are cycled using an electrically controllable local-heating mechanism for the forward reaction and catalyzed by a single charge-transfer process for the reverse switching. This single-molecule device can be modulated in situ, is fully reversible, and does not display stochastic switching. The I–V curves of this single-molecule system also exhibit memristive character. These features suggest a new approach for the development of molecular switching systems and storage-class memories.     

The special features of the crystal structure and properties of oxides with mixed conductivity based on lanthanum gallate

The paper presents a review of works on the synthesis, structural composition effects, phase transitions, and electrical conductivity properties of multicomponent solid solutions based on heterosubstituted lanthanum gallate (La,A)(Ga,M)O_{3 ? y} . High-temperature phase transitions and structural and charge ordering effects were studied. The presence of iron cations in different valence states was proved; the relative contents of these cations depended on the x parameter and nonstoichiometry parameter y of the base composition. For M = Fe, antiferromagnetic ordering was observed; its temperature interval was determined by the concentration of iron cations in the high-spin state. The total conductivity was found to increase as the concentration of transition metal cations grew because of an increase in the electronic conductivity component. The data on structural parameters and dc and ac conductivity substantiated the conclusion that the highest ionic conductivity and permeability to oxygen were characteristic of iron-containing oxides. The results obtained are evidence that crystal chemical factors play a determining role in the formation of the ion-conducting properties of anion-deficient perovskite-like oxides.     

Metal-oxide surfaces

Over the past two decades the amount of effort devoted to the study of metal oxides by surface scientists has increased significantly. The general characteristics of the electronic structure of metal-oxide surfaces are now fairly well understood, although transition-metal oxides have been more thoroughly studied than have non-transition-metal oxides. The geometric arrangement of atoms on the surfaces of a variety of metal oxides has also been determined. Extensive studies have been performed of the interaction of both molecules and metal atoms with metal oxides, where point defects are found to play a dominant role. However, our understanding of the surface properties of metal oxides is still much less compete than it is for metals and semiconductors, and there are several areas where more experimental and theoretical effort needs to be concentrated.