Single Oxidation State Research Articles

Surface study of lead magnesium niobate ceramic using X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to study the surface of ceramic lead magnesium niobate (PMN) when sintered at 1000 °C under two different conditions. Two oxidation states have been observed for Pb in PMN covered with MgO powder during sintering (PSM1000) whereas Pb exhibited a single oxidation state when fired without MgO cover (2P1000). A shoulder peak Pb(4f 7/2) at 136.7 eV binding energy has been assigned to PbO 2 separate from the PbO peak at 138.0 eV in PSM1000 whereas the single Pb(4f 7/2) peak at 138.1 eV has been assigned to PbO in 2P1000. The XPS depth profiles on PSM1000 confirm the existence of PbO 2 in the bulk. The higher dielectric constant of the MgO-covered samples compared with uncovered is attributed to the difference in lead valencies.

Photoreduction Study of Mo Allyl-Based Mo/SiO2 Catalysts

X-ray photoelectron spectroscopy (XPS or ESCA) measurements were performed on a photoreduced Mo allyl-based Mo/SiO{sub 2} catalyst (1.7 wt % Mo). Photoreduction was carried out in CO at room temperature for increasing lengths of time. Factor analysis, deconvolution, and curve fitting were used to determine the number and positions of components present in the series of XPS Mo 3d spectra obtained for the oxidic and photoreduced Mo/SiO{sub 2} catalyst. The results indicated the formation of a single oxidation state Mo{sup x+} (Mo 3d{sub 3/2} binding energy at 232.1 eV) after 2 h of photoreduction and the appearance of Mo{sup 4+} as in MoO{sub 2} (Mo 3d{sub 3/2} binding energy at 230.2 eV) with continued photoreduction. Average oxidation state studies indicated that the species designated as Mo{sup x+} should also be assigned to Mo{sup 4+} but in an environment different than that of MoO{sub 2}. 36 refs., 6 figs., 2 tabs.

Synthesis and Structure of NaMn 3(PO 4)(HPO 4) 2, an Unoxidized Variant of the Alluaudite Structure Type

Sodium manganese(II) phosphate bis(hydrogenphosphate), NaMn 3(PO 4)(HPO 4) 2, has been prepared hydrothermally and its structure has been determined from single-crystal diffraction data. It crystallizes in space group C 2/ c of the monoclinic system with Z = 4 in a cell of dimensions a = 12.179(2) Å, b = 12.405(1) Å, c = 6.6602(8) Å, and β = 114.616(7)°. The structure consists of a complex network of edge-sharing Mn(II)O 6 octahedral chains that are linked together by both corner-sharing PO 4 tetrahedra and O-H···O bonds, forming channels along which Na atoms reside. The structure thus represents an unoxidized variant of the alluaudite structure type, containing Mn atoms in only the single oxidation state of + II. The structure is embellished by the presence of hydrogen bonds, evidence for which was obtained from bond-valence calculations, infrared spectroscopy, and thermal measurements which suggest the loss of one H 2O molecule per formula unit. Magnetic susceptibility measurements confirm the assignment of high-spin Mn 2+ in the title compound, as well as in its dehydrated form.

Bindungslängen-Bindungsstärken-Beziehungen für Oxide von 4p-, 5p- und 6p-Elementen

Abstract Bond-length-bond-strength relationships which are valid for different oxidation states of the elements have been established for oxides of As, Se, Br, Pb and Bi. According to new structural data, such relationships of single oxidation states in oxides of Ga(III), Ge(IV), In(III), Tl(I) and Tl(III) have been recalculated as well as those for oxides of Sn, Sb, Te, and I.

Bindungslängen – Bindungsstärken-Beziehungen für Oxide von 4d- und 5d-Elementen

Abstract Bond-length – bond-strength relationships which are valid for different oxidation states of the metals have been established for oxides of Ru, Rh, Pd, Ag, Re, Os, Ir, and Hg, and for single oxidation states in oxides of Tc(VII) and Au(III). According to new structural data, such relationships have also been recalculated for Y(III), La(III), Zr, Hf(IV), and Cd(II). Exceptions are discussed.

Construction of Multicomponent Pourbaix Diagrams Using Generalized Species

A method for the construction of predominance‐zone diagrams of multicomponent and multiphase systems of chemical species in a single oxidation state, which consider the formation of mixed and polynuclear complexes (of the type) is presented. Such diagrams may be constructed by defining generalized species, complexation coefficients (with multiplicative structure) and generalized equilibria of complexation, dismutation, polynucleation, and phase formation, with their conditional constants associated. By having these diagrams for each oxidation state of the same component, multidimensional Pourbaix diagrams are constructed. The predominance‐zone diagrams of *Eu(0), *Eu(II), and *Eu(III) in the presence of citric acid and nitrilotriacetic acid in aqueous solution, are constructed by using this approach.

The effect of heat treatment on the structural properties of electron-beam-evaporated SnO2 films

Thin films of SnO2 are deposited by an electron beam evaporation method under controlled deposition conditions. The effect of substrate temperature and post-deposition annealing temperature on the structural properties of the films are studied to obtain good SnO2 films for gas sensor application. Scanning electron microscopy results show that the films deposited by this method are uniform and continuous after annealing. It is observed from the X-ray diffraction (XRD) results that the films deposited at lower substrate temperatures are amorphous and become polycrystalline SnO at 350 °C. The films, when annealed, reach the final oxidation state SnO2 either through the single oxidation state SnO or through two oxidation states SnO and Sn3O4, depending on the deposition temperature. It is further observed from XRD and transmission electron microscopy results that the films deposited at 25 and 350 °C and annealed at 600 °C are pure polycrystalline SnO2 films with a larger grain size, which are expected to be suitable for gas sensor application. The films deposited at intermediate substrate temperatures and annealed at 600 °C exhibit mixed phases, with a smaller grain size.

Auger study of interfacial reaction between sputter-deposited NiTi films and a glass substrate containing titanium oxide

The interfacial reaction between magnetron sputter-deposited NiTi films and various glass substrates, namely silica glass, borosilicate glass and borosilicate glass containing titanium oxide, were studied. It was found that the glass substrate containing titanium oxide showed a broad transition region (20–30 nm) in which the titanium-to-nickel and silicon-to-oxygen ratios varied markedly with depth. In accordance with the existence of a broad transition region, the shapes of O KLL Auger lines showed a continuous change in the oxide species through the transition region. In contrast, the interface between NiTi films and borosilicate and silica glasses showed only a narrow transition region indicating that no interfacial interaction occured during or after the sputter deposition. These facts suggest that titanium oxide dissolved in borosilicate glass plays an important role. The results are discussed on the basis of the thermodynamics for oxide formation. It is shown that the existence of various oxidation state for titanium and a single oxidation state for silicon and boron are responsible for the difference in the widths of the transition regions observed in the three different substrates.

Multiple-bonding configurations for oxygen on silicon surfaces

Using high-resolution core-level spectroscopy we show that up to four different oxidation states of silicon coexist even at monolayer oxygen coverage. This observation precludes current models with a single adsorption geometry. Below 0.2 monolayer coverage, a single oxidation state is seen but the (100) surface has an oxygen-bonding geometry different from the (111) surface evidenced by different valence states and work-function changes.

The polarographic measurement of O2, Fe2+, Mn2+, and S2− in hypolimnetic water

Anoxic hypolimnetic waters can he investigated by differential pulse and DC sampled polarography. A single scan can measure dissolved oxygen and ferrous, manganous, and sulfide ions in less than 3 min. The unique properties of the hypolimnion, enhanced concentrations and freedom from oxygen, enable direct measurement without pretreating the water sample. Filtration is unnecessary because an electrochemical kinetic technique measures only labile ionic species of a single oxidation state.

A Versatile X-Ray Fluorescence Method for the Analysis of Sulfur in Geologic Materials

AbstractNonproportionality of X-ray fluorescence intensity vs. concentration of sulfur occurs in geologic materials prepared as ground samples. Samples containing sulfur as sulfate yield higher intensities than an equivalent amount of sulfur as the Sulfide. Although the intensity of free sulfur decreases markedly during a short exposure to X-rays in a vacuum, and sulfide intensities decrease over a much longer time period, sulfate intensities show no deterioration with time.A fusion procedure utilizing a LiBO2-Ce(NH4)2(NO3)5 flux has been developed for geologic materials to oxidize all sulfur in a multiplicity of oxidation states to a single oxidation state, namely, the sulfate. The procedure is applicable over a wide range of concentrations (0.5 - 28 wt. % total sulfur) with a detection limit of 0.01%. A suite of chemically analyzed rocks containing both sulfides and Sulfates is used for standardization.

A mathematical interpretation of catalysis derived from infrared spectroscopyII. reactions of H and H2 with O, OH, and H2O

Experimental data are presented on the activities reported for metals and compounds in the formation of water by catalysis of the reaction of hydrogen and oxygen and by reduction of metal oxides. The Intermedion Theory is used to predict metals which should catalyze reactions of H and H2 with O, OH, and H2O. Predictions and experiment are in agreement with respect to the metals and in many cases with respect to chemical oxidation state as well. Other metals which are not good catalysts or components of oxidants to form water are not found among the metals predicted for these reactions. Restricting the reactants at the catalytic site to a single oxidation state limits the number of metals predicted to such an extent that differences in reaction mechanism become clearly apparent. Certain oxidation states of Cr, Fe, Cu, Ag, Co, and Ni catalyze the reaction of polarized chemisorbed hydrogen molecules and oxygen atoms to form water directly in a single step. Other metals, such as, Mn, Ru, Ir, Pd, and Pt catalyze successive steps through OH and H3O+ intermediates. The catalytic species active in these reactions are Cr4+, Fe4+, Co4+, Ru2+, and Ru3+, Mn3+ and Mn4+, Mn6+ and Mn7+, and Ni3+. The possibility that “intermedions” are one class of the long-sought activated intermediates of catalysis is supported by these results.