Correlation of Oxygen Storage Capacity and Structural Distortion in Transition-Metal-, Noble-Metal-, and Rare-Earth-Ion-Substituted CeO2 from First Principles Calculation

Oxygen storage/release (OSC) capacity is an important feature common to all three-way catalysts to combat harmful exhaust emissions. To understand the mechanism of improved OSC for doped CeO2, we undertook the structural investigation by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H-2-TPR (temperature-programmed hydrogen reduction) and density functional theoretical (DFT) calculations of transition-metal-, noble-metal-, and rare-earth (RE)-ion-substituted ceria. In this report, we present the relationship between the OSC and structural changes induced by the dopant ion in CeO2. Transition metal and noble metal ion substitution in ceria greatly enhances the reducibility of Ce1-xMxO2-delta (M = Mn, Fe, Co, Ni, Cu, Pd, Pt, Ru), whereas rare-earth-ion-substituted Ce(1-x)A(x)O(2-delta) (A = La, Y) have very little effect in improving the OSC. Our simulated optimized structure shows deviation in cation oxygen bond length from ideal bond length of 2.34 angstrom (for CeO2). For example, our theoretical calculation for Ce28Mn4O62 structure shows that Mn-O bonds are in 4 + 2 coordination with average bond lengths of 2.0 and 3.06 angstrom respectively. Although the four short Mn-O bond lengths spans the bond distance region of Mn2O3, the other two Mn-O bonds are moved to longer distances. The dopant transition and noble metal ions also affects Ce coordination shell and results in the formation of longer Ce-O bonds as well. Thus longer cation oxygen bonds for both dopant and host ions results in enhanced synergistic reduction of the solid solution. With Pd ion substitution in Ce1-xMxO2-delta (M = Mn, Fe, Co, Ni, Cu) further enhancement in OSC is observed in H-2-TPR. This effect is reflected in our model calculations by the presence of still longer bonds compared to the model without Pd ion doping. The synergistic effect is therefore due to enhanced reducibility of both dopant and host ion induced due to structural distortion of fluorite lattice in presence of dopant ion. For RE ions (RE = Y, La), our calculations show very little deviation of bonds lengths from ideal fluorite structure. The absence of longer Y-O/La-O and Ce-O bonds make the structure much less susceptible to reduction.

Ce0.78Sn0.2Pt0.02O2-delta: A new non-deactivating catalyst for hydrogen production via water-gas shift reaction

We demonstrate the activity of Ce0.78Sn0.2Pt0.02O2-delta, a new catalyst, towards water-gas shift (WGS) reaction. Over 99.5% CO conversion to H-2 is observed at 300 +/- 25 degrees C. Based on different characterization techniques we found that the present catalyst is resistant to deactivation due to carbonate formation and sintering of Pt on the surface when subjected to longer duration of reaction conditions. The catalyst does not require any pre-treatment or activation between start-up/shut-down reaction operations. Formation of side products such as methane, methanol, formaldehyde, coke etc. was not observed under the WGS reaction conditions indicating the high selectivity of the catalyst for H-2. Temperature programmed reduction of the catalyst in hydrogen (H-2-TPR) shows reversible reduction of Ce4+ to Ce3+, Sn4+ to Sn2+ and Pt4+ to Pt-0 oxidation state with oxygen storage capacity (OSC) of 3500 mu mol g(-1) at 80 degrees C. Such high value of OSC indicates the presence of highly activated lattice oxygen. CO oxidation in presence of stoichiometric O-2 shows 100% conversion to CO2 at room temperature. The catalyst also exhibits 100% selectivity for CO2 at room temperature towards preferential oxidation (PROX) of residual CO in presence of excess hydrogen in the feed. (C) 2010 Elsevier B.V. All rights reserved.

Studies in nonlinear optical materials: structure of di-2-menthyl 2-(N,N'-dimethyl-2-imidazolidinylidene)malonate monohydrate

C28H48N2Oa.H2 O, Mr=494.7, orthorhombic,P2~2~2~, a = 7.634 (2), b = 11.370 (2), c=34. 167 (4) A, V = 2966 (2) A 3, Z = 4, D m = 1.095,D x -- 1. 108 g cm -3, Mo Kct, 2 -- 0.7107 ,/k, ~ =0.43 cm -~, F(000) = 1088.0, T= 293 K, R = 0.061 for 1578 significant reflections. The second-harmonicgeneration (SHG) efficiency of this compound is negligible (1/100th of the urea standard). The observed low second-order nonlinear response has been attributed to the unfavourable packing of the molecules in the crystal lattice.

Thermodynamics of Cobalt (II, III) Oxide (Co3O4): Evidence of Phase Transition

The Gibbs' energy change for the reaction, 3CoO (r.s.)+1/2O2(g)→Co3O4(sp), has been measured between 730 and 1250 K using a solid state galvanic cell: Pt, CuO+Cu2O|(CaO)ZrO2|CoO+Co3O4,Pt. The emf of this cell varies nonlinearly with temperature between 1075 and 1150 K, indicating a second or higher order phase transition in Co3O4around 1120 (±20) K, associated with an entropy change of ∼43 Jmol-1K-1. The phase transition is accompanied by an anomalous increase in lattice parameter and electrical conductivity. The cubic spinel structure is retained during the transition, which is caused by the change in CO+3 ions from low spin to high spin state. The octahedral site preference energy of CO+3 ion in the high spin state has been evaluated as -24.8 kJ mol-1. This is more positive than the value for CO+2 ion (-32.9 kJ mol-1). The cation distribution therefore changes from normal to inverse side during the phase transition. The transformation is unique, coupling spin unpairing in CO+3 ion with cation rearrangement on the spinel lattice, DTA in pure oxygen revealed a small peak corresponding to the transition, which could be differentiated from the large peak due to decomposition. TGA showed that the stoichiometry of oxide is not significantly altered during the transition. The Gibbs' energy of formation of Co3O4 from CoO and O2 below and above phase transition can be represented by the equations:ΔG0=-205,685+170.79T(±200) J mol-1(730-1080 K) and ΔG0=-157,235+127.53T(±200) J mol-1(1150-1250 K).

Mean square displacements of hydrogen interstitial and its neighbours in the intermetallic compound Fe0.5Ti0.5

A Green's function technique is used in the scattering matrix formalism to compute the mean square displacement of hydrogen and deuterium interstitials in the intermetallic compound Fe0.5Ti0.5 for low hydrogen/deuterium concentration. The mean square amplitudes of the metal atoms surrounding the interstitial are found to be smaller than those for the host crystal. This anomalous effect is due to the stiffening of the lattice by the dissolved hydrogen or deuterium at low concentration. This type of effect is experimentally observed in the case of NbHx at low hydrogen concentration.

Polymeereillä stabiloitu amorfinen formulaatio

Nowadays growing number of new active pharmaceutical ingredients (API) have large molecular weight and are hydrophobic. The energy of their crystal lattice is bigger and polarity has decreased. This leads to weakened solubility and dissolution rate of the drug. These properties can be enhanced for example by amorphization. Amorphous form has the best dissolution rate in the solid state. In the amorphous form drug molecules are randomly arranged, so the energy required to dissolve molecules is lower compared to the crystalline counterpart. The disadvantage of amorphous form is that it is unstable. Amorphous form tends to crystallize. Stability of amorphous form can be enhanced by adding an adjuvant to drug product. Adjuvant is usually a polymer. Polymers prevent crystallization both by forming bonds with API molecules and by steric hindrance. The key thing in stabilizing amorphous form is good miscibility between API and polymer. They have to be mixed in a molecular level so that the polymer is able to prevent crystallization. The aim of this work was to study miscibility of drug and polymer and stability of their dispersion with different analytical methods. Amorphous dispersions were made by rotary evaporator and freeze dryer. Amorphicity was confirmed with X-ray powder diffraction (XRPD) right after preparation. Itraconazole and theophylline were the chosen molecules to be stabilized. Itraconazole was expected to be easier and theophylline more difficult to stabilize. Itraconazole was stabilized with HPMC and theophylline was stabilized with PVP. Miscibility was studied with XRPD and differential scanning calorimetry (DSC). In addition it was studied with polarized light microscope if miscibility was possible to see visually. Dispersions were kept in stressed conditions and the crystallization was analyzed with XRPD. Stability was also examined with isothermal microcalorimetry (IMC). The dispersion of itraconazole and theophylline 40/60 (w/w) was completely miscible. It was proved by linear combination of XRPD results and single glass transition temperature in DSC. Homogenic well mixed film was observed with light microscope. Phase separation was observed with other compositions. Dispersions of theophylline and PVP mixed only partly. Stability of itraconazole dispersions were better than theophylline dispersions which were mixed poorer. So miscibility was important thing considering stability. The results from isothermal microcalorimetry were similar to results from conventional stability studies. Complementary analytical methods should be used when studying miscibility so that the results are more reliable. Light microscope is one method in addition to mostly used XRPD and DSC. Analyzing light microscope photos is quite subjective but it gives an idea of miscibility. Isothermal microcalorimetry can be one option for conventional stability studies. If right conditions can be made where the crystallization is not too fast, it may be possible to predict stability with isothermal microcalorimetry.

High-temperature dielectric response in pulsed laser deposited Bi1.5Zn1.0Nb1.5O7 thin films

Cubic pyrochlore Bi1.5Zn1.0Nb1.5O7 thin films were deposited by pulsed laser ablation on Pt(200)/SiO2/Si at 500, 550, 600, and 650 degrees C. The thin films with (222) preferred orientation were found to grow at 650 degrees C with better crystallinity which was established by the lowest full-width half maxima of similar to 0.38. The dielectric response of the thin films grown at 650 degrees C have been characterized within a temperature range of 270-650 K and a frequency window of 0.1-100 kHz. The dielectric dispersion in the thin films shows a Maxwell-Wagner type relaxation with two different kinds of response confirmed by temperature dependent Nyquist plots. The ac conduction of the films showed a varied behavior in two different frequency regions. The power law exponent values of more than 1 at high frequency are explained by a jump-relaxation-model. The possibility of grain boundary related large polaronic hopping, due to two different power law exponents and transformation of double to single response in Nyquist plots at high temperature, has been excluded. The ``attempt jump frequency'' obtained from temperature dependent tangent loss and real part of dielectric constants, has been found to lie in the range of their lattice vibronic frequencies (10(12)-10(13) Hz). The activation energy arising from a large polaronic hopping due to trapped charge at low frequency region has been calculated from the ac conduction behavior. The range of activation energies (0.26-0.59. eV) suggests that the polaronic hopping at low frequency is mostly due to oxygen vacancies. (C) 2010 American Institute of Physics. doi:10.106311.3457335]

Reactivity studies of highly electrophilic ruthenium complexes

The 16-electron, coordinatively unsaturated, dicationic ruthenium complex Ru(P(OH)(2)(OMe))(dppe)(2)]OTf](2) (1a) brings about the heterolysis of the C-H bond in phenylacetylene to afford the phenylacetylide complex trans-Ru(C CPh)(P(OH)(2)(OMe))(dppe)(2)]OTf] (2). The phenylacetylide complex undergoes hydrogenation to give a ruthenium hydride complex trans-Ru(H)(P(OH)(2)(OMe))(dppe)(2)]OTf] (3) and phenylacetylene via the addition of H-2 across the Ru-C bond. The 16-electron complex also reacts with HSiCl3 quite vigorously to yield a chloride complex trans-Ru(Cl)(P(OH)(2)(OMe))(dppe)(2)]OTf] (4). On the other hand, the other coordinatively unsaturated ruthenium complex Ru(P(OH)(3))(dppe)(2)]OTf](2) (1b) reacts with a base N-benzylideneaniline to afford a phosphonate complex Ru(P(O)(OH)(2))(dppe)(2)]OTf] (5) via the abstraction of one of the protons of the P(OH)(3) ligand by the base. The phenylacetylide, chloride, and the phosphonate complexes have been structurally characterized. The phosphonate complex reacts with H-2 to afford the corresponding dihydrogen complex trans-Ru(eta(2)-H-2)(P(O)(OH)(2))(dppe)(2)]OTf] (5-H2). The intact nature of the H-H bond in this species was established using variable temperature H-1 spin-lattice relaxation time measurements and the observation of a significant J(H,D) coupling in the HD isotopomer trans-Ru(eta(2)-HD)(P(O)(OH)(2))(dppe)(2)]OTf] (5-HD). (C) 2010 Elsevier B. V. All rights reserved.

Theory of unitarity bounds and low-energy form factors

We present a general formalism for deriving bounds on the shape parameters of the weak and electromagnetic form factors using as input correlators calculated from perturbative QCD, and exploiting analyticity and unitarily. The values resulting from the symmetries of QCD at low energies or from lattice calculations at special points inside the analyticity domain can be included in an exact way. We write down the general solution of the corresponding Meiman problem for an arbitrary number of interior constraints and the integral equations that allow one to include the phase of the form factor along a part of the unitarity cut. A formalism that includes the phase and some information on the modulus along a part of the cut is also given. For illustration we present constraints on the slope and curvature of the K-l3 scalar form factor and discuss our findings in some detail. The techniques are useful for checking the consistency of various inputs and for controlling the parameterizations of the form factors entering precision predictions in flavor physics.

Grain Growth in ECAE Processed Pure Magnesium

Grain growth kinetics was studied for commercially pure magnesium subjected to equal channel angular extrusion (ECAE). The specimens were ECAE processed upto 4 passes at 523 K following all the three important routes, namely A, 13, and C. Texture and microstructures of the samples were studied using Electron Back Scattered Diffraction (EBSD) technique in a Field Emission Gun Scanning Electron Microscope (FEG-SEM). It was observed that the grain size significantly reduces after ECAE. ECAE process produces a slightly rotated B and C-2 fiber. Static annealing leads to normal grain growth with unimodal distribution of grains through out the temperature range. Average activation energy for grain growth in the temperature range studied is found to be less than the activation energy for lattice diffusion and grain boundary diffusion of magnesium. No significant change in texture during isochronal annealing for 1 hour i.e., the predominant deformation texture remains same.

Two-stage photoquenching in semi-insulating GaAs:EL2

The photoquenching of EL2 in semi‐insulating gallium arsenide is seen to be a complex process, where at low temperatures the initial slow quenching is followed by a switch to fast quenching. A possible explanation involving lattice strain mediated cooperative structural relaxation arising out of transition to the metastable state is proposed.

Disorder-driven electronic localization and phase separation in superconducting Fe1+yTe0.5Se0.5 single crystals

We have investigated the influence of Fe excess on the electrical transport and magnetism of Fe1+yTe0.5Se0.5 (y=0.04 and 0.09) single crystals. Both compositions exhibit resistively determined superconducting transitions (T-c) with an onset temperature of about 15 K. From the width of the superconducting transition and the magnitude of the lower critical field H-c1, it is inferred that excess of Fe suppresses superconductivity. The linear and nonlinear responses of the ac susceptibility show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is a magnetic coupling between Fe excess occupying interstitial sites in the chalcogen planes and those in the Fe-square lattice. The temperature derivative of the resistivity d(rho)/d(T) in the temperature range T-c < T < T-a with T-a being the temperature of a magnetic anomaly, changes from positive to negative with increasing Fe. A log 1/T divergence of the resistivity above T-c in the sample with higher amount of Fe suggests a disorder-driven electronic localization.

Thermoelectric properties of electrostatically tunable antidot lattices

We report on the fabrication and characterization of a device which allows the formation of an antidot lattice (ADL) using only electrostatic gating. The antidot potential and Fermi energy of the system can be tuned independently. Well defined commensurability features in magnetoresistance as well as magnetothermopower are observed. We show that the thermopower can be used to efficiently map out the potential landscape of the ADL. (C) 2010 American Institute of Physics. doi: 10.1063/1.3493268]