Raymond G. Teller

New materials synthesis: Characterization of some metal-doped antimony oxides

Abstract In order to understand the chemistry of altermetal dopants in antimony oxide, the detailed structural characterization of two β-Sb 2 O 4 compounds is reported, Mo-doped β-Sb 2 O 4 (1.5 metal%) and V-doped β-Sb 2 O 4 (5 metal%). The methods used to character...

Structural analysis of metastable pseudobrookite ferrous titanium oxides with neutron diffraction and mossbauer spectroscopy

Abstract Four synthetic iron titanium oxides with the pseudobrookite (AB2O5, Cmcm, Z = 4) structure have been prepared and characterized by neutron diffraction and zero-field, natural abundance 57Fe Mossbauer effect spectroscopy (MES). The combination of the element specificity of MES with the different neutron scattering lengths of Ti and Fe (−0.33 and 0.95 × 10−12 cm, respectively) offers a unique opportunity to distinguish between cation distributions on the two (“A” and “B”) sites. Two of the samples have been prepared in low temperature experiments (quenched from 1200°C) and have the stoichiometry FeTi2O5, and Fe.6Mg.6Ti1.8O5. The third and fourth samples are commercial iron titanium oxides prepared by the reduction of ilmenite ore with carbon above 1700°C. The stoichiometries of these samples are Mn0.05Fe0.33Ti2.52O5 and Fe.33Mg.31Ti2.36O5. Results from these experiments indicate that for each of these samples the B site is predominantly (>65%) occupied by Ti, while the A site contains a mixture of Ti, Fe, and/or Mg. However, only at higher temperatures (>1700°C) is the B site devoid of ferrous cations. These results suggest that an “ordered” model for ferrous titanium-rich oxides of the pseudobrookite structure (100% Ti occupancy of the B site) is descriptive only at elevated temperatures, and that at lower temperatures a “disordered” model (partial iron occupation of the B site) is a more accurate representation of the structure. Because of this difference, it may be possible to predict the thermal history of naturally occurring samples based on cation distributions.

The chemistry of the thermal decomposition of pseudobrookite ferrous titanium oxides

Abstract The thermal decomposition of two metastable ferrous titanium oxide compounds of commercial interest have been studied by in situ X-ray and neutron diffraction at elevated temperatures as well as by 57Fe Mossbauer effect spectroscopy. Thermal decomposition was monitored by collecting neutron diffraction data (taken at the Argonne National Laboratory Intense Pulsed Neutron Source (IPNS) powder diffractometers) at 30-min intervals at 900 and 1000°C. Previous work has shown that each of these materials (pseudobrookite structure, AB2O5), (Mn0.05Fe0.33Ti0.52)(Ti2.0)O5 and (Mg0.21Fe0.33Ti0.46)(Ti1.9Mg0.1)O5, has a significant amount of Ti in the +3 oxidation state and is completely ordered (no Fe located in the “B” site). The results of these “in situ” diffraction studies show that, prior to the thermal decomposition of the slags, there is a redistribution of cations within the pseudobrookite structure. Specifically, at temperatures in the range 600–700°C, iron cations move from the “A” sites to the “B” sites and Ti cations move from the “B” to the “A” sites. It is after this order-disorder transition that decomposition commences. At temperatures above 900°C, the neutron diffraction data show at least two modes of decomposition describing the high temperature chemistry of these disordered materials. The first mode produces iron metal and rutile (TiO2) and is modeled by the equation 2Fe0.5Ti2.5O5 → Fe + 5TiO2. The second mode of decomposition produces an iron-doped titanium oxide of the rutile structure and is modeled by the equation 4M0.3Ti2.7O5 → 2M0.5Ti2.5O5 + 5Fe0.04Ti1.16O2 (M = Fe2+, Mn2+, Mg2+).

The X-ray structures of H5Re(PMe2Ph)3 and H7Re(PMe2Ph)2

Abstract The structures of H5Re(PMe2Ph)3 and H7Re(PMe2Ph)2 have been solved by single-crystal X-ray diffraction methods. Although the hydride ligands could not be directly located in this study, the overall structure of the complexes could be deduced from a knowledge of the central rhenium/phosphorus core of the molecules. The ReP3 skeleton of H5Re(PMe2Ph)3 has distorted pyramidal geometry (PReP angles 149.5°, 101.9°, 99.8°) consistent with dodecahedral structure for the H5ReP3 core. The ReP2 backbone of H7Re(PMe2Ph)2 is bent (PReP angle 146.8°), suggesting a tricapped trigonal prismatic geometry for the H7ReP2 core in which the P atoms are placed in opposing axial and equatorial positions. Crystallographic details: H5Re(PMe2Ph)3: space group P21/c (monoclinic); a = 6.876(3) A, b = 19.493(7) A, c = 19.646(8) A, β = 103.26(2)°, V = 2563.0 A3, Z = 4; R = 6.7% for 2067 reflections. H7Re(PMe2Ph)2: space group P21/n (monoclinic); a = 19.083(17) A, b = 6.337(4) A, c = 15.234(13) A, β = 93.72(4)°, V = 1834.0 A3, Z = 4; R = 5.0% for 1672 reflections.