The microstructure of the Ti-doped MgB 2 which shows a significantly improved critical current density, J c ͓Appl. Phys. Lett. 79, 1154 ͑2001͔͒, is investigated. It is found that Ti does not occupy the atomic site in the MgB 2 crystal structure, but forms a thin TiB 2 layer ͑with a thickness about one unit cell of TiB 2 ͒ in the grain boundaries of MgB 2 . Besides, MgB 2 grains are greatly refined by Ti doping, forming a strongly coupled nanoparticle structure. It is argued that the unique microstructure of the MgB 2 nanoparticles with TiB 2 nanograin boundaries may take responsibility for the enhancement of J c in the Ti-doped MgB 2 bulk superconductor.

As part of an investigation of new cathode materials for intermediate temperature solid oxide fuel cells, we have investigated several perovskite oxides with cobalt ions on the B sites in both bulk and thin film forms. Of particular interest is the composition La 0.5 Sr 0.5 CoO 3-x (LSCO) which has exceptional properties for oxygen reduction at intermediate temperatures in ceria based fuel cells. Thin films of LSCO were deposited on both sides of a dense polycrystalline gadolinia doped ceria substrate by pulsed laser deposition under conditions that lead to the formation of nanocrystalline films. The electrochemical properties for oxygen reduction were determined in a symmetric electrochemical cell by alternating current (AC) impedance spectroscopy. The results were analyzed using the Adler-Lane-Steele (ALS) model to obtain the diffusion and surface exchange coefficients and the thermodynamic factor. We show that the thermodynamic factor, a measure of how easy it is to create oxygen vacancies, is much higher than observed in conventional cathodes. As a result, the electrode composition changes little with temperature and oxygen partial pressure, the large chemical contribution to the thermal expansion is reduced, and the electrode has good stability. The use of a nanostructured electrode does not significantly affect the fundamental material parameters (surface exchange and diffusion coefficients), and the very low area specific resistance (0.09 ohm cm 2 at 600 °C) observed is because the synthesis method gives a very high surface area (80 μm -1 ).

Highly oriented ionic conductor gadolinium-doped CeO2−δ (Ce0.8Gd0.2O2−δ) thin films have been grown on single-crystal (001) MgO substrates by pulsed-laser ablation. The films are highly c-axis oriented with cube-on-cube epitaxy, as shown by x-ray diffraction and electron microscopy. The interface relationship is, surprisingly, found to be (001)film//(001)sub and [100]film//[100]sub with an extremely large lattice misfit of more than 28%. Ac impedance measurements in the temperature range of 500 to 800 °C reveal that electrical conductivity is predominantly ionic over a very broad oxygen partial pressure range from pO2 from 1×10−19 atm to 1 atm. The activation energy Ea for ionic conductivity measured on unannealed films is 0.86 eV, but after heat treatment, Ea decreases to 0.74 eV.

Monodispersed, uniformly alloyed Pt 3 Co alloy nanoparticle electrocatalysts were synthesized via reduction of metallic precursors by sodium borohydride in heptane/polyethylene glycol dodecylether (Brij)/water reverse micelles. These particles were further adsorbed on XC-72R carbon powder, separated from micelles, and characterized using X-ray diffraction (XRD), transmission electronic microscopy (TEM). The electrochemical activity for the oxygen reduction reaction (ORR) was characterized using a Rotating Disk Electrode (RDE) technique. Even though residual surfactants on the metallic nanoparticle reduced the active surface area of the electrocatalytic particles, the catalytic activity of the prepared Pt 3 Co nanoparticles exhibited higher Pt mass and Pt surface area specific activities compared to pure Pt. The impact of heat treatment on the mean particle size, the electrochemical surface area (ESA), and on the activity was investigated and correlated to the residual surfactant coverage. Intermediate annealing temperatures resulted in larger ESA, despite particle growth pointing to lower surfactant coverage. Higher annealing temperatures caused large particle growth and reduced ESA, yet significant activity gains. A surface segregation mechanism resulting in a catalytically active Pt skin structure is hypothesized.

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