Structure Of Transition Metal Oxides Research Articles

Hund's second rule and the electronic structure of transition-metal oxides

An orbital polarization (Hund's second rule) correction to local spin density (LSD) theory is developed in both a spherical harmonic basis and in a crystal field basis, and applied to the electronic band structure of FeO, CoO, NiO, and La2CuO4, resulting in a substantial enhancement of the LSD insulating band gap for NiO, and the creation of insulating band gaps for FeO, CoO, and La2CuO4.

The X-ray Absorption Near Edge Structure of transition metal oxides: A one-electron interpretation

We have used a one-electron, multiple-scattering computational scheme to calculate the X-ray Absorption Near-Edge Structure (XANES) for a series of crystalline oxides of the 3 d transition metals from Ca to Cu, and compare them with our high-resolution experimental data on the cation K-edges. Virtually every feature of the experimental spectra is replicated by our theory, both in energy and relative intensity. The effects of charge self-consistency have been investigated for the most ionic of these substances, CaO, and found to be small.

Relative stabilities of layered perovskite and pyrochlore structures in transition metal oxides containing trivalent bismuth

In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d 0 cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO 6 octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi 4Ti 3O 12 cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi 1.33V 2O 6, Bi 2O 3, and Bi metal. The distortion of Bi 1.33V 2O 6 to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi 2NbCrO 7, Bi 2NbFeO 7, TlBiM 2O 7 ( M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb 2O 7.

Chemisorption and the electronic structure of transition metal oxides and transition metals bonded to oxide surfaces

Abstract Some simple transition metal oxides such as NiO have incomplete atomic subshells and yet are highly insulating. This implies a high degree of electronic localization and also indicates that the chemical bonds are saturated. In this respect these oxides are similar to alkaline earth oxides such as MgO. The analogy extends to their surface properties. MgO and NiO, for example, are both good catalysts although a pure, perfect surface of either seems inactive. It is argued that defects or impurities are required to activate the perfect surface and that catalytic properties relate weakly, at best, to the nature of the cation. These oxides are contrasted with the more studied industrial catalyst which consists of a group of transition metal ions bonded to an oxide surface. The electronic structure properties which determine the behaviour of such catalysts are explored in terms of the unrestricted Hartree-Fock model augmented with explicit inclusion of correlation. The results obtained produce a satisfactory band structure and describe surface prupcrties adequately.

Ferroelectricity and the structure of transition-metal oxides

Ferroelectricity and the structure of transition-metal oxides