Ternary Transition Metal Oxides Research Articles

Effect of V substitution at B-site on the physicochemical and electrocatalytic properties of spinel-type NiFe 2O 4 towards O 2 evolution in alkaline solutions

Spinel-type ternary transition metal oxides of nickel, iron and vanadium with composition NiFe 2 − x V x O 4 (0 ≤ x ≤ 1) have been synthesized by a hydroxide precipitation method and investigated for their physicochemical and electrochemical catalytic properties towards the oxygen evolution reaction (OER) in alkaline solutions at 25 °C. The OER study indicates that substitution of V from 0.25 to 1.0 mol for Fe in the spinel matrix increases the electrocatalytic activity of the oxide greatly; the activity being the greatest with x = 0.5 mol. At low overpotentials, the Tafel slope and the order for the OER with respect to OH − concentration were found to be ∼40 mV and ∼2, respectively.

Low‐Temperature Nanoparticle‐Directed Solid‐State Synthesis of Ternary and Quaternary Transition Metal Oxides.

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Low-Temperature Nanoparticle-Directed Solid-State Synthesis of Ternary and Quaternary Transition Metal Oxides

Ternary and quaternary transition metal oxides, which offer a wide variety of important physical properties, are traditionally synthesized using high-temperature reactions that often require several days of heating. A new nanoparticle-directed approach for the rapid low-temperature synthesis of nanocrystalline bulk-scale ternary and quaternary transition metal oxides has been developed. Readily available metal oxide nanoparticles can serve as a robust toolkit of highly reactive reagents, which can be mixed in solution in known ratios to form nanomodulated precursors and rapidly transformed, at relatively low temperatures, into more complex oxides. This approach is initially demonstrated for pyrochlore-type Y2Ti2O7 and Eu2Ti2O7 using XRD, DSC, and TEM to monitor the reaction. A nanocomposite of Y2O3 and TiO2 nanoparticles transforms into nanocrystalline Y2Ti2O7 within 2 h of heating to 700 °C, and Eu2Ti2O7 forms within 2 h of heating a nanocomposite of Eu2O3 and TiO2 nanoparticles to 800 °C. NiTiO3, CoTiO3...

22 New compounds and structures in the solid state

The discovery of new compds. and structures in the solid state has continued to fluorish during 2002. One particular highlight involves the use of CaH2 as a high temp. reducing agent for ternary transition metal oxides to prep. LaSrCoO3H0.7 that adopts an unprecedented structure contg. oxide chains that are bridged by hydride anions to form a 2-dimensional extended network. Another highlight, found within the area of microporous materials, includes the synthesis of the new zeolite ITQ-21 (Si0.66Ge0.34O2) that has a 3-dimensional pore network contg. 11.8 .ANG. wide cavities, each of which is accessible through six 7.4 .ANG. diam. circular 12-ring windows. As in last years report, and those by previous reviewers, this review will provide an overview of the most significant developments reported over the last year and focus on new compds., mainly with novel structure types, contg. extended inorg. lattices. [on SciFinder (R)]

Electrical transport and small polaron hopping conduction in Mn-doped Bi3PbSr3Ca3Cu4−mMnmOx glasses: precursors for high temperature superconductors

Abstract Multicomponent Bi3PbSr3Ca3Cu4−mMnmOx (m=0, 0.02, 0.03, 0.04, and 0.06) glasses, precursors for high temperature superconductors, have been prepared by fast quenching technique from their melts. These are n-type semiconductors and follow non-adiabatic small polaron hopping conduction mechanism above 1 2 θ D (where θD being the Debye temperature). The lower temperature (below 1 2 θ D ) conductivity data can be fitted with the variable range hopping (VRH) model. The estimated Mott parameters are found to be reasonable for the formation of small polaron and comparable with those of some other similar glasses. However, compared to the usual binary or ternary transition metal oxide glasses, the density of states at the Fermi level N(EF) is found to be one order of magnitude higher which we consider to be due to the formation of nanocrystalline (5–20 nm) clusters in these glasses. All the glasses are found to become superconductors in their glass–ceramic phases and the corresponding superconducting transition temperature decreases continuously with increase of Mn content indicating pair-breaking mechanism.

Electronic structure of ternary transition metal oxides and sulphides: X-ray photoelectron and X-ray emission spectroscopy study

Results of measurements of X-ray photoelectron spectra (XPS) and X-ray emission spectra (XES) of constituents atoms (excited by electrons and tunable synchrotron radiation) of ternary transition metal oxides (EuMnO 3, Sr 2RuO 4) and sulphides (BaCo 1−xNi x S 2 are presented. They are compared with LDA and LDA + U band structure calculations. For Sr 2RuO 4 and BaCo 1− x Ni x S 2 energy excitation dependence of O Kα and S L 2,3 XES near the O 1s and S 2p threshold is found which is attributed to excitation of inequivalent oxygen and sulphur atoms in plane and apical sites, and corresponding O 2p and S 3s3d DOS are mapped.

REDUCED ALKALINE EARTH TANTALATES

Among reduced ternary transition metal oxides, tantalates are rare, even though interesting electronic properties might be expected. Here, we report on new reduced alkaline earth tantalates Ca 2Ta 2O 6F, Sr 3-xTa 5O 15, and Ba 2Ta 15O 32 grown under vacuum conditions and high temperatures. These reduced ternary tantalates are isostructural with known reduced ternary niobates, indicating a strong similarity of the crystal chemistry between the two systems. © 1997 Elsevier Science Ltd

Magnetic phase diagrams of CoNb 2O 6

The ternary transition metal oxide CoNb 2O 6 is a quasi-one-dimensional magnetic material build by zig-zag chains with ferromagnetic intrachain interaction. The chains are weakly coupled by competing antiferromagnetic interactions exhibiting a sinusoidally modulated incommensurate phase, an antiferromagnetic ground state and several field induced spin-flip phases with n-fold unit cell. The magnetic phase diagrams obtained by neutron diffraction for several field directions are presented.

On oxides of monovalent transition metals

Density functional theory (DFT) calculations were performed on the dioxometallate(I) anions [MO 2] 3− for MCu, Ni, Co, Fe in ternary alkali metal transition metal oxides A 3MO 2. The crystal surrounding was simulated by Madelung field. The influence of the surrounding alkali metal ions was examined. The electronic structure differs from that of the isoelectronic dihalides M′X 2 (M′ = M + 1). Orbital mixing is more pronounced in [MO 2] 1−. The M3d− π g atomic orbital (a.o.) correlates in [MO 2] 3− with an antibonding M3 d− O2 p−π g ∗ molecular orbital (m.o.), the M3d− σ ga.o. correlates with a strongly mixed nonbonding M3d−4s− σ g hybrid-m.o. There is significant covalency in the dioxometallate(1) anions in contrast to the more ionic dihalides. As a result the orders of calculated levels are different in some cases. The charge distribution may be symbolized by [M 28−O 2 11.5−δ 1−]. The MO bond length varies significantly with the π g ∗ occupation. The assignment of the electronic ground states and electronic spectra is still an unsolved problem. Its solution would throw light on the reliability of present-day DFT approaches.

Composition–Valence Diagrams: A New Representation of Topotactic Reactions in Ternary Transition Metal Oxide Systems. Application to Lithium Intercalation

Topotactic reactions in Li–M–O systems withM= Mn, Ti, V, Fe are described in the framework of composition–valence diagrams, using the Li/Mand the transition metal valence ν(M) as coordinates. We show that this representation is very convenient to depict and compare the various parameters associated with insertion/extraction reactions, i.e., the evolution of ν(M), the extent of intercalationxin LixMOy, the electrochemical potentials, and the cell parameter changes. New directions are suggested for topotactic reaction in oxides, especially in titanium ones. The composition–valence diagram helped in the detection of inconsistencies in the intercalation potentials in LiFe5O8, which are corrected using new voltammetric data. We conclude that lithium intercalation in octahedral sites of iron spinel oxides occurs at constant voltage around 1.6 V, whichever the Li–Fe–O host may be.

Hydrothermal synthesis of transition metal oxides under mild conditions

A notable development in mild (≤ 200°C) hydrothermal synthesis in the past few years has been the extension of the synthesis technique from zeolites and metal phosphates to binary and ternary transition metal oxides. This low-temperature technique is critical to the formation of metastable phases not obtainable using traditional high-temperature methods. New phases, as well as known materials, of the oxides of tungsten, molybdenum, vanadium and manganese have been formed, often in highly crystalline form. One enhancement of the technique is microwave heating, which appears to accelerate nucleation, producing very uniform particles in a few hours.

Synthesis and magnetic and electrical properties of new ternary chromium oxides with the rutile structure

Tetragonal M'MSbO6 (M'= Cr, Rh; M = V, Ru) with rutile-type structures have been reported and characterized recently. [1-3]. The ternary transition metal oxides have incompletely filled d shells, and the variations of the observed structures and physical properties are associated with the number of unpaired d electrons. Often these properties (structural, magnetic, electrical, etc.) can be modified by changing some Of the M cations in the rutile structure. This letter reports the synthesis and magnetic and electrical behaviour of new compounds in the quaternary system Cr-MIV-Sb-O2 (MtV= Ti, Ge, Sn, Te).

Synthesis and Structure of Two New Ternary Nitrides: FeWN2 and MnMoN2

New layered ternary transition metal nitrides, FeWN2 and MnMoN2, were synthesized in single-step reactions by the ammonolysis of ternary transition metal oxides. Solid-state precursors FeWO4 and MnMoO4 were treated with ammonia at 625 and 800 °C to yield the ternary nitrides FeWN2 (P63/mmc; a = 2.87630(5) Å, c = 10.9320(4) Å) and MnMoN2 (P63/mmc; a = 2.92262(8) Å, b = 10.8564(4) Å), respectively. Structures are proposed on the basis of Rietveld analysis of powder X-ray diffraction data. These compounds are members of a family of layered hexagonal ternary nitrides, consisting of alternating layers of MN6 (M = Fe, Mn) octahedra and M‘N6 (M‘ = W, Mo) trigonal prisms. The conductivity data for both compounds indicate metallic-like behavior.

Why are some oxides metallic, while most are insulating?

A large variety of undoped binary and ternary transition metal oxides, including formally divalent, trivalent and tetravalent metal cations, have been examined. These 76 compounds are classified as either “metals”, “insulators”, or having a “metal-to-insulator” transition. In an attempt to understand these variations, the Zaanen-Sawatzky-Allen framework was used in which each compound can be characterized by three parameters: the Coulomb correlation or disproportionation energy ( U′), the charge-transfer energy (Δ) and the bandwidth ( W). Assuming W is constant, we have calculated U′ and Δ using a simple ionic model, which includes only the gas phase ionization potentials and the bare electrostatic Coulomb interactions between the ions. With this model, the occurence of metallic conductivity is remarkably well accounted for in these oxides.

Ternary Transition Metal Oxide Phases of the Fluorite Structure.

Ternary Transition Metal Oxide Phases of the Fluorite Structure.