Cation inter-diffusion between LaMnO3 and LaCoO3 materials

Cation inter-diffusion between polycrystalline LaMnO₃ and LaCoO₃ pellets has been studied at 1373-1673 K in air by electron microprobe analysis. Inter-diffusion coefficients were evaluated by the Boltzman-Matano method from Mn³⁺ to Co³⁺ concentration profiles. The cation inter-diffusion is thermally activated and follows Arrhenius behaviour. The activation energies have been calculated and the mechanism for the B-site cation diffusion in La(Mn,Co)O₃ solid solution suggested. Cation diffusion coefficients in the end members LaMnO₃ and LaCoO₃ were estimated. Cation mobility in LaMnO₃ is higher than in LaCoO₃. It is suggested that higher cation diffusion in LaMnO₃ is due to the specific defect chemistry of this material, caused by the relative stability of manganese in a higher oxidation state (Mn⁴⁺). The results are compared to previous reports on cation diffusion in perovskite oxides.     

Synthesis and electro‐optical characterization of new conducting PEDOT/Au‐nanorods nanocomposites

This paper describes a new strategy to obtain PEDOT/Au‐nanorods nanocomposites with different PEDOT: Au ratio. A polymeric ionic liquid (PIL) was used as stabilizer during the chemical synthesis of PEDOT dispersions. PEDOT/Au‐nanorods dispersions in organic media were obtained. Electrochemical characterization of PEDOT/Au‐nanorods nanocomposites revealed that the addition of Au nanorods modified the electroactivity of the conducting films by reducing the oxidation potential from +0.33 to +0.23 V (versus Ag/AgCl). Optical contrast (ΔT%) of the films decreased from 17% for neat PEDOT films to 8% for PEDOT/Au‐nanorods nanocomposites films (3:1 (v/v)) while switching times (from 1 to 4 sec) were similar to neat PEDOT. Conductivity of the films increased from 0.027 S/cm for neat PEDOT to 0.691 S/cm for PEDOT/Au‐nanorods nanocomposites. Nanoscale morphology and contact potential of PEDOT/Au‐nanorods nanocomposites were investigated in detail by Scanning Force Microscopy. Electrical measurements show a clear contact potential difference between the ITO substrate and the PEDOT/Au‐nanorods film. On the film, no contact potential inhomogeneity is observed indicating that the Au‐nanorods are uniformly dispersed in the film. Copyright © 2010 John Wiley & Sons, Ltd.     

Cluster ion emission from LiF induced by MeV N<Superscript>q+</Superscript> projectiles and <Superscript>252</Superscript>Cf fission fragments

Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N ^q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A ²⁵²Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments (FF). Emission of (LiF) _n Li⁺ clusters are observed for both the N beams and the ²⁵²Cf fission fragments. The observed cluster size n varies from 1 to 6 for N ^q+ projectiles and from 1 to ≈40 for the ²⁵²Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF) _n F⁻ closely resembles that of the positive secondary (LiF) _n Li⁺ ions. The desorption yields of positive ions scale as Y(n) ∼ q ⁵. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S _e ³ with the electronic stopping power S _e , as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions.     

RAFT “grafting-through” approach to surface-anchored polymers: Electrodeposition of an electroactive methacrylate monomer

The synthesis of homopolymer and diblock copolymers on surfaces was demonstrated using electrodeposition of a methacrylate-functionalized carbazole dendron and subsequent reversible addition-fragmentation chain transfer (RAFT) “grafting-through” polymerization. First, the anodically electroactive carbazole dendron with methacrylate moiety (G1CzMA) was electrodeposited over a conducting surface (i.e. gold or indium tin oxide (ITO)) using cyclic voltammetry (CV). The electrodeposition process formed a crosslinked layer of carbazole units bearing exposed methacrylate moieties. This film was then used as the surface for RAFT polymerization process of methyl methacrylate (MMA), styrene (S), and tert-butyl acrylate (TBA) in the presence of a free RAFT agent and a free radical initiator, resulting in grafted polymer chains. The molecular weights and the polydispersity indices (PDI) of the sacrificial polymers were determined by gel permeation chromatography (GPC). The stages of surface modification were investigated using X-ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM) to confirm the surface composition, thickness, and film morphology, respectively. UV-Vis spectroscopy also confirmed the formation of an electro-optically active crosslinked carbazole film with a p \pi - p^* \pi^{{\ast}}_{} absorption band from 450-650nm. Static water contact angle measurements confirmed the changes in surface energy of the ultrathin films with each modification step. The controlled polymer growth from the conducting polymer-modified surface suggests the viability of combining electrodeposition and grafting-through approach to form functional polymer ultrathin films.     

De Vries smectic A phase formed by a liquid crystal side chain copolymer? A 13C NMR study

We study the orientation and order parameter of a liquid crystalline random side chain copolymer by ¹³C NMR. Evidence has previously been presented that this material forms a de Vries smectic A phase. The NMR data show that the molecular tilt angle in the smectic A phase is very small or zero and the smectic A-smectic C* transition is attributed predominantly to a change of the molecular tilt rather than azimuthal ordering. We discuss the NMR results in the context of earlier X-ray and elastic characterizations of structurally similar materials.     

Classic and multivariate modeling treatment of the kinetics and mechanism of isomerization of 5‐cholesten‐3‐one catalyzed by sodium ethoxide

A classic kinetic methodology including the treatment of the steady‐state method and a multivariate modeling kinetic treatment were applied to the kinetics and mechanism of the isomerization reaction of 5‐cholesten‐3‐one to 4‐cholesten‐3‐one catalyzed by EtO⁻ in ethanol absolute. The rate constants, thermodynamic parameters of activation, equilibrium constant, and the isomerization enthalpy were determined. The multivariate modeling kinetic treatment allows us to calculate the concentrations of the species, in which the 3,5‐dienolate is included as a highly reactive intermediate species and was able to discriminate among several applicable mechanisms validating the one comprising two reversible steps. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 38–47, 2006     

Structural evolution of small gold clusters doped by one and two boron atoms

The potential energy surfaces (PES) of a series of gold–boron clusters with formula Au_nB (n = 1–8) and Au_mB₂ (m = 1–7) have been explored using a modified stochastic search algorithm. Despite the complexity of the PES of these clusters, there are well‐defined growth patterns. The bonding of these clusters is analyzed using the adaptive natural density partitioning and the natural bonding orbital analyses. Reactivity is studied in terms of the molecular electrostatic potential. © 2014 Wiley Periodicals, Inc.     

Active manganese dioxide promoted cyclization of ortho-(1H-pyrrol-1-yl)aryl and heteroaryl carboxylic acids to 5H-pyrrolo[1,2-a][3,1]benzoxazin-5-one derivatives

The hitherto unknown lactone 5H-pyrrolo[1,2-a][3,1]benzoxazin-5-one and six of its substituted derivatives have been prepared by active manganese dioxide promoted oxidative cyclization of the corresponding 2-(1H-pyrrol-1-yl)benzoic acids, under mild conditions, in moderate yields. The method was successfully extended to the cyclization of some ortho-(1H-pyrrol-1-yl)heteroaryl carboxylic acids and 2-(1H-indol-1-yl)benzoic acids.