M. DeMarco

Tris(5-methylpyrazolyl)methane: synthesis and properties of its iron(II) complex.

The new ligand, tris(5-methylpyrazolyl)methane (1), has been prepared by the reaction of n-butyl lithium with tris(pyrazolyl)methane followed by trimethylation of the tetralithiated species with methyl iodide. The BF(4)(-), ClO(4)(-), and BPh(3)CN(-) salts of the Fe(II) complex of this ligand were also synthesized. The X-ray crystal structure of the BF(4)(-) complex (2) at 100 K had Fe-N bond lengths of 1.976 Å, indicative of a low spin Fe(II) complex, while at room temperature, the structure of this complex had a Fe-N bond distance close to 2.07 Å, indicative of an admixture of approximately 50% low-spin and 50% high-spin. The solid-state structure of the complex with a ClO(4)(-) counterion was determined at 5 different temperatures between 173 and 293 K, which allowed the thermodynamic parameters for the spin-crossover to be estimated. Mössbauer spectra of the BF(4)(-) complex further support spin-state crossover in the solid state with a transition temperature near 300 K. UV-visible spectroscopy and (1)H NMR studies of 2 show that the transition temperature in solution is closer to 400 K. No spin-crossover was observed for [Fe(1)(2)](2+)·2BPh(3)CN(-). The results allow the separation of effects of groups in the 3-position from those in the 5-position on tpm ligands, and also point toward a small cooperative effect in the spin-crossover for the Fe(II) complex.

Reversible NOx storage over Ru/Na–Y zeolite

Ruthenium loaded Na–Y zeolite was found to be an efficient adsorbent for achieving NOx adsorption–desorption cycles comprising adsorption under oxidizing and desorption under reducing conditions. The speciation of ruthenium was investigated using TEM, EXAFS, 99Ru Mossbauer spectroscopy and XRD in combination with Rietveld refinement. The sodium cation siting was monitored using 23Na MAS NMR. Characterization of the Ru/Na–Y adsorbent in NOx saturated and regenerated state revealed a unique cooperation of supported ruthenium nano metal particles and isolated Ru atoms in framework cavities affecting the sodium cations. Supported ruthenium nanoparticles assume a catalytic role in NO oxidation. Ruthenium atoms in framework cavities undergo switching of oxidation state during adsorption–desorption cycles. It triggers reversible sodium cation migrations from coordination with the framework in the regenerated state to coordination in sodium–water networks in supercages providing adsorption sites for NOx during adsorption. The peculiar ruthenium organization is naturally obtained upon lean–rich cycling. Ru/Na–Y adsorbent is insensitive to SOx and to the presence of CO during reductive regeneration.

Functional ITO coatings on glasses by RF plasma mist technique in ambient atmosphere

Abstract Recently, we developed an RF plasma mist deposition technique in ambient atmosphere. Indium tin oxide films have been coated on soda—lime—silicate and fused silica glass substrates, at deposition temperatures ranging from 400 to 750°C. As-deposited films are uniform and homogeneous as revealed by scanning electron microscopy, atomic force microscopy and energy dispersive spectroscopy, X-ray diffraction indicated that either indium oxide (In 2 O 3 ) or tin oxide (SnO 2 ) is formed depending on the indium-to-tin ratio (In:Sn). Average sizes of crystallites in the films are between 6 and 35 nm. Furthermore, as-deposited films are nearly 100% transparent in the visible range and the maximum conductivity occurs near In:Sn ratio of 9:1. Other material properties, such as the optical absorption edge and lattice parameters are also dependent on the In:Sn ratio.

Anomalous electronic and magnetic properties of the Eu2Ru2O7 pyrochlore

Structural, 99Ru Mossbauer, dc and ac susceptibility magnetization, and magneto-transport properties of the polycrystalline Eu2Ru2O7 pyrochlore are reported in this paper. From the experimental data, we deduce that the ruthenium cations Ru4+ (S = 1) are surrounded by an unusual electronic environment, involving conduction electron polarization and extrinsic Eu3+ ions at low temperature. This situation leads to an anomalous spin-glass transition at 23 K.

Magnetoresistance, magnetic, and dielectric properties of LuFe2O4 prepared by ebeam-assisted solid state reaction

We present structural, magnetoresistance, magnetic, Mossbauer, and dielectric properties of polycrystalline LuFe 2O 4 prepared by an electron-beam assisted solid state reaction. The x-ray diffraction pattern shows the single phase LuFe 2O 4 sample, and the ferrimagnetic transition temperature is measured at 240 K, followed by the two low-temperature transitions at 210 K and 140 K, respectively. The magnetic properties including the M-H hysteresis loops exhibit a strong temperature dependence and possibly indicate that LuFe 2O 4 enters a spin-glass state below 100 K. The iron Mossbauer measurement at 300 K indicates two Fe sites. The resistivity follows Mott’s variable-range hopping model, ρ∝exp(T0/T)1/4, indicating the electron hopping between Fe 2+ and Fe 3+. The magnetoresistance effects up to 2.5% at 5 T in the ferrimagnetic state were observed, and the effects could be caused by the field-induced changes in the electron hopping processes. The frequency-dependent complex dielectric constant has been found to be strongly influenced by the contact effects, and the intrinsic ferroelectricity of LuFe 2O 4 could not be ascertained.We present structural, magnetoresistance, magnetic, Mossbauer, and dielectric properties of polycrystalline LuFe 2O 4 prepared by an electron-beam assisted solid state reaction. The x-ray diffraction pattern shows the single phase LuFe 2O 4 sample, and the ferrimagnetic transition temperature is measured at 240 K, followed by the two low-temperature transitions at 210 K and 140 K, respectively. The magnetic properties including the M-H hysteresis loops exhibit a strong temperature dependence and possibly indicate that LuFe 2O 4 enters a spin-glass state below 100 K. The iron Mossbauer measurement at 300 K indicates two Fe sites. The resistivity follows Mott’s variable-range hopping model, ρ∝exp(T0/T)1/4, indicating the electron hopping between Fe 2+ and Fe 3+. The magnetoresistance effects up to 2.5% at 5 T in the ferrimagnetic state were observed, and the effects could be caused by the field-induced changes in the electron hopping processes. The frequency-dependent complex dielectric constant has been f...

Oxygen removal by hydrogen gas in 57Fe doped YBa2Cu3Ox

Abstract We have studied the YBa 2 Cu 3 O x compounds using the Fe Mossbauer effect as a function of hydrogen reduction. This technique does not alter the orthorhombic crystal structure of the compound for short reduction times. On the other hand, oxygen is removed and the T c of the sample is reduced in the process. The Mossbauer effect measurements show that oxygen leaves five-fold coordinated Cu (1) sites and creates planar oxygen coordinated sites. Mossbauer measurements in the insulating 1-2-3 phase show that there are only four and six-fold oxygen coordinations around the Cu (1) site. Some impurity phases have been created in the initial fabrication process and the Mossbauer effect shows that these impurity phases could transform to magnetic phases during the reduction process.

Iron substitution in Y2BaCuO5 and YBa2Cu3O7−y

A few atomic percent of 57Fe has been substituted for Cu in the YBa2Cu3O7−y system. Air‐annealed samples are the superconducting 1‐2‐3 compound YBa2Cu3−x57FexO7−y while nitrogen‐annealed samples are mainly the nonsuperconducting 2‐1‐1 compound Y2BaCu1−x57FexO5. X–ray, Meissner effect, and thermogravimetric measurements have been made on both compounds. The site dependence has been studied and compared in these two compounds by the Mossbauer effect with the result that Fe prefers the Cu(l) site in the 1‐2‐3 compound.

Mossbauer Effect Studies in YBa2Cu3−YSnYO7−x

We have measured the Sn Mossbauer Effect in YBa2Cu3−YSnYO7−x samples. The samples have been analyzed using thermogravimetric and magnetometer analysis. The Mossbauer measurements show a broadened line that can be fit with two sets of Quadrupoles that indicate two different oxygen vacancy sites in the 1–2–3 compounds.