Nanocrystalline (<100 nm) red emitting Eu3+- doped M3Al2O6 (M = Ba, Ca and Sr) phosphors were prepared by an aqueous sucrose-PVA-metal ion complex route. The aqueous sucrose-PVA solution includes 20 mol% PVA, and the method is based on the dehydration of a transparent metal ion-sucrose-PVA solution to a highly viscous liquid and then precursor formation by heating at 250°C. The phase formation and the crystallite size measurements were made by x-ray diffraction techniques. Photon correlation analysis revealed that all synthesized phosphor particles range in size from 400 nm to a few microns. The photoluminescence (PL) and PL excitation characteristics have been investigated. All samples have broad CT bands centered at around 269 nm and only the Ca3Al2O6:Eu3+ exhibited the characteristic f-f transitions of Eu3+ ions mainly located at 396 and 465 nm in comparable levels with the CT band. The emission spectrum of Ca3Al2O6:Eu3+ is dominated by the red (5D0 ¡æ 7F2) transition band located at 614 nm, however the Eu3+ doped Sr3Al2O6 and Ba3Al2O6 phosphors have comparable emission intensity in the red (5D0 ¡æ 7F2 ) and orange (5D0 ¡æ 7F1 ) transition bands. The highest intensity of the red emission was obtained when the Ca3Al2O6:Eu3+ phosphor was excited at 396 nm.

Perovskite-type oxides are promising materials with potential use as dense membranes for oxygen separations. We herein report slow crack growth (SCG) studies of La0.2Sr0.8Fe0.8Cr0.2O3-δ (LSFCO) perovskite membranes as Oxygen Transport Membranes (OTM). Two sample batches of perovskite were tested to investigate the effect of temperature, specific chemical environments, and loading rate on flexure strengths, using four-point bending tests. The first batch was examined at room temperature in air. The second batch was soaked in a N2/air atmosphere at 1000°C for 1 hour prior to application of load. Loading rates varied from 0.00005 mm/s to 0.01 mm/s. Flexural strength data indicate that the examined OTM material showed little susceptibility to SCG at room temperature in air. However, the sample is susceptible to SCG in a N2/air environment at 1000°C. Also, the experiments demonstrate flexural-strength rate dependency, with strength increasing with the loading rate. The observed phenomena are explained by the decomposition and microstructural transitions in the perovskite. The results provide important information about OTM mechanical degradation, which is valuable for future OTM design applications.

We have investigated the effect of various dopants on the sintering characteristics of Ce0.9Gd0.1O1.95 (CGO) and found that 99% dense electrolyte pellets can be produced at the record low temperature of 800°C (as opposed to the 1400°C typically needed) by sintering Ce0.9Gd0.1O1.95 with as little 3mol% lithium. Our studies indicate that doping the CGO surface with lithium nitrate, as opposed to using alternative lithium salts, produces the largest decrease in sintering temperature. Unlike other dopants that lower the sintering temperature by altering the near grain boundary vacancy concentration, lithium lowers the sintering temperature through the formation of an intergranular liquid phase. This liquid phase allows fully dense, completely constrained CGO films to be produced on inert substrates at temperatures as low as 950°C.

Thin films of 8 mol% yttria-stabilized zirconia (YSZ) of thickness ranging from 15nm-500nm have been deposited on Si3N4(90nm)/Si substrates by RF sputtering at room temperature. These samples have been studied using in situ ion scattering techniques including Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA) to analyze the oxygen distribution and defect chemistry as a function of annealing in various oxidizing and reducing ambient upto 500°C. In addition, the structural quality of these films after long time annealing has been investigated using grazing incidence X-ray diffraction (GIXRD). Temperature dependent X-ray absorption spectroscopy (XAS) has been performed to study the unoccupied density of states and chemical nature of YSZ. In this paper, we will discuss in detail the effects of annealing in different ambient on the defect chemistry, structure and stability of films in these materials systems.

The influence of local structure variations on the charge transport properties are still not well understood at an atomic level. In this work the experimentally observed drastic conductivity enhancement in epitactic stacks of BaF2:CaF2 heterolayers compared to any of the two fluoride ion conducting phases is reproduced by molecular dynamics simulations and analyzed in detail with particular emphasis on the variation of properties with the distance to the two-phase boundary. Ion mobility varies with the distance to the interface but remains significantly enhanced throughout the modeled layers when compared to bulk materials.

The bond valence method is utilized to study correlations between the conductivity enhancement and the microstructure. A time-averaged violation of local electroneutrality postulated in the mesoscopic multiphase model is verified by the bond valence analysis of the molecular dynamics simulation trajectories. The variation of the ion mobility can be related to the extension of clusters of unoccupied accessible pathway regions.

Ceria-zirconia samples doped with Gd, Pr, Sm, or La cations were prepared via Pechini route and promoted by Pt. Effect of their real structure and surface properties (characterized by neutronography, EXAFS, XPS, FTIRS of adsorbed CO) on the mobility and reactivity of the lattice oxygen (by oxygen isotope exchange and CH4 TPR) was analyzed. For the reaction of CH4 steam reforming (SR), catalytic performance is determined both by Pt dispersion and lattice oxygen mobility. Ni-YSZ anodes promoted by these catalysts possess a stable and efficient performance in CH4 SR in the 600-800°C range in stoichiometric feeds without coking.

Nanostructured YSZ+NiO anodes (fuel electrode) for solid oxide fuel cell (SOFC) were developed by plasma spraying. Influence of processing parameters was correlated with deposit microstructure and properties. During particle in-flight with in the plasma jet, the high temperatures of plasma resulted in an increase in average crystallite size; the nanostructure was, however, conserved. Anodes with well distributed finely porous nanostructure exhibiting high gas permeability, suitable high temperature electronic conductivity, enhanced triple phase boundaries and catalytic activity were produced by controlling plasma enthalpy and velocity. Properties of nanostructured anodes were compared with conventional ones. At room temperature the permeability of nanostructured anodes was an order of magnitude higher than their conventional counter parts whereas in-plane conductivity at 800°C in reducing atmosphere of former was 4% higher than that of the latter. Electrochemical performance of optimized nanostructured anode was compared with conventional NiO+YSZ anodes by testing full cells at 800°C. 9.5 mol% YSZ electrolyte and LSM cathode were deposited onto these anodes for electrochemical testing in static and dynamic conditions. Impedance spectroscopy measurements were performed to collect data on polarization resistance and catalytic behavior of anode layers. Gas and temperature variation on both cells was performed and data was compared. It was established that enlarged reaction zone provided by high specific surface area of nanostructured anodes and finely porous microstructure led to lower activation and concentration polarizations and enhanced cell performance by more than 30% compared to conventional cells. During redox (oxidation and reduction of nickel in anode electrode) cycling the cell composed of nanostructured anode exhibited lower degradation.

The electronic structure of nanolaminate Ti2AlC and Ti2AlN thin films, so-called MAX-phases, were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitride compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti L-emission of Ti2AlC and Ti2AlN that is not present in the binary TiC system. The spectral shape of Al L-emission in the MAX-phase is strongly modified in comparison to metallic Al. By replacing or partly exchanging C with N, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the material properties.

Nanoporous Ti (and TiOx) has been formed by anodization of RF sputtered titanium thin films. A solution of 1M (NH4)2SO4 (ammonium sulphate) electrolytes containing 0.5wt% (NH4)F (ammonium fluoride) was used in the anodization process. Different nano and micro structures were obtained. Voltage in a rage of 2 to 10V was employed in the process. It was observed that the magnitude of applied voltage have a significant impact in the formation of different surface morphologies with various nano/micro structures. The anodized titanium thin films were characterised using scanning electron microscopy and X-ray diffraction techniques.

Nanostructured anodic alumina membranes have been utilized as high-temperature stable supports for 150 nm thick continuous palladium films. The palladium has been deposited by vacuum evaporation onto the rotating substrate. The thermal stability of the resulting compound membranes has been demonstrated for temperatures up to 700ºC under a reducing atmosphere. Hydrogen permeation has been measured up to 280ºC, where the permeability has a value of 2.5·10-7 mol m-2 s-1 Pa-1. At the same time the selectivity factor over carbon dioxide is at least 33.

Erbium(III) doped TiO2 nanofibers (Er2Ti2O7) have been synthesized by electrospinning mixtures of polymers, metal-containing materials, and erbium acetate. These electrospun nanofibers were subsequently annealed at temperatures of 550, 750, 950, and 1150 oC to remove the organics and leave behind the metal oxides. The crystal structure and optical properties of the nanofiber pyrochlores were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformation IR (FTIR) spectroscopy. Different crystal structures were formed by controlling the annealing conditions. XRD data are compared with near-IR spectra to better understand the effects of annealing temperature on the Er (III) thermally-excited selective optical emission process.

Homogeneous sub-micron sized particles of surface carbon coated phase pure LiFePO4 are synthesized by a novel non-aqueous oxalate-based sol-gel route. X-ray diffractogram of LiFePO4 reveals nanocrystals with average crystallite size 32(7) nm. The very large QS (nearly five times greater than that of Fe3+) value observed from Mossbauer spectrum is due to high spin configuration of 3d electrons and the asymmetric local environment at Fe site in LiFePO4. A uniform particle size distribution with grain size 100 - 150nm was observed in SEM with few irregular growths. Our synthetic route successfully overcomes the incidence of Fe3+, effectively controls undesirable particle growth and has the potential for upscaling and application as Li-ion battery cathodes. Progressive evolution of olivine structure by the interlock of FeO6 octahedra and PO4 tetrahedra with Li concentration is studied by introducing lithium in to LixFePO4 (0.0 × 1.0 ). A fairly abrupt phase transformation from monoclinic Fe3(PO4)2 to orthorhombic LiFePO4 shows up for x∼0.2 accompanied by structural disorder which gets stabilized at x 0.35. A systematic study of X-ray diffractograms shows nanocrystal nucleation and growth from an unstable low symmetry crystalline phase with considerable disorder.