New Oxide Membranes for Methane Conversion
A mixed electron - ion conducting oxide membrane reactor separates oxygen from air on one side of the membrane. Selective hydrocarbon oxidation-for example, conversion of natural gas into valuable synthesis gas (CO and H2)-occurs on the other side. Membrane reactors for converting methane to synthesis gas offer significant economic incentives because they eliminate the need for a dedicated oxygen separation system.

We are investigating new oxides with the perovskite structure in order to discover materials with improved properties for use as membranes in gas conversion. We have found recently that La0.5Sr0.5Fe0.8Ga0.2O3-x (LSFGO) has many desirable properties. We have developed a process for synthesis of chemically homogeneous LSFGO as determined by electron microprobe analysis. Conductivity measurements and membrane permeation studies on dense ceramics show that LSFGO has high total conductivity and good oxygen transport properties. Chemical stability is excellent at the low oxygen partial pressures and high temperatures (950°C) required in a methane conversion membrane reactor.

High Rate Deposition of Zirconia Films by Reactive Sputtering
Zirconia stabilized with yttria (YSZ) is at present the electrolyte of choice in solid oxide fuel cells. Synthesis of high quality films of YSZ at rapid deposition rates is important for cost reduction and lower temperature operation of solid oxide fuel cells and in other applications. We have shown that sputtering from very hot targets can solve the problems of rate instability and arcing that are typically encountered in the DC-reactive sputtering of oxide thin films. Using a Research S-gun we have achieved high deposition rates of dense stoichiometric films of YSZ. To compare with other techniques, one must look at the ratio of the maximum YSZ deposition rate to that of the pure metal. Our measured ratio (1.5/1) is about three times larger than the best result in the literature, obtained by pulsed DC-magnetron deposition.

Chemical Vapor Deposition of Cerium Dioxide Films
Cerium dioxide has important applications in sensors, three way catalysts and when doped with samaria as an electrolyte for low temperature solid oxide fuel cells. Cerium oxide can be deposited by chemical vapor deposition from cerium _-diketonate precursors, but these compounds have low volatility and must be heated to high temperatures to increase their vapor pressure. The high temperatures cause decomposition, which results in vapor pressure fluctuation, non-reproducible precursor delivery and poor films. To circumvent these problems, we have synthesized new thermally stable and volatile cerium alkoxide complexes for use as precursors to cerium oxide. Low-pressure chemical vapor deposition using one of our new alkoxides as a single-source precursor yielded high quality CeO2 films at 400 °C.

Self Propagating High Temperature Synthesis of Multi-Component Oxide Powders for Fuel Cell Applications
Solid oxide fuel cells (SOFCs) are an environmentally clean, quiet, and a highly efficient method for generating electrical power from natural gas and other fuels. The development of lower cost materials and ceramic manufacturing processes for these devices is important for their widespread introduction. We have investigated the use of self-propagating high temperature synthesis (SHS) as a cost-effective way of synthesizing complex multi-component powders for use in this application. We have shown that SHS can be used to efficiently synthesize La0.8Sr0.2MnO3 which is close in composition to the cathode material used in cathode supported tubular SOFCs. The electrical conductivity is comparable to that of materials prepared by conventional methods.

Ion Transport Across Interfaces
High performance ionic devices (fuel cells, membrane reactors, sensors) require rapid ion transport across both gas-solid and solid-solid interfaces. The microscopic processes that determine interface transport are complex and difficult to obtain from measurements on 'real' devices. Epitaxial oxide films on single crystal substrates are better-defined systems that can be used to study important details of interface ion transport. We have grown high quality La0.5Sr0.5CoO3 thin films on single crystals of the solid electrolyte yttria stabilized zirconia (YSZ) and infused them by reaction with labeled oxygen (18O2). The 18O profiles measured by nuclear reaction analysis were used to determine the two bulk and interface transport parameters. The profile of 18O in the YSZ substrate allows calibration of the experiment. Significantly, the profile shows no break across the interface between the two materials, indicating insignificant resistance to this inter-phase oxide ion transfer.

A General Synthesis of Homoleptic Indium Alkoxide Complexes and the Chemical Vapor Deposition of Indium Oxide Films
Seigi Suh and David M. Hoffman*
A general synthetic route to homoleptic indium alkoxide complexes was developed and one of the new compounds was used as a precursor to transparent, conductive indium oxide films. The amide complex In[N-t-Bu(SiMe3)]3 reacted with t-BuOH, EtMe2COH, Et2MeCOH and i-PrMe2COH to give the dimers [In(_-OR)(OR)2]2, R = t-Bu, CMe2Et, CMeEt2 and CMe2i-Pr, in high yield. The compounds [In(O-i-Pr)3]n and In[(_-OCHEt2)2In(OCHEt2)2]3 were also prepared by reacting [In(_-O-t-Bu)(O-t-Bu)2]2 with an excess of the respective alcohols. The reaction between In[N-t-Bu(SiMe3)]3 and 2,6-diisopropylphenol afforded the bis t-butylamine adduct In(O-2,6-i-Pr2C6H3)3(H2N-t-Bu)2. The powerful donor p-dimethylaminopyridine (p-Me2Npy) reacted with [In(_-O-t-Bu)(O-t-Bu)2]2 to give 5-coordinate In(O-t-Bu)3(p-Me2Npy)2 and with the more sterically encumbered complex [In(_-OCMeEt2)(OCMeEt2)2]2 to yield four-coordinate In(OCMeEt2)3(p-Me2Npy). In addition, [In(_-O-t-Bu)(O-t-Bu)2]2 reacted with 2,2,6,6-tetramethyl-3,5-heptanedione (t-Bu2-_-diketone) to afford (t-BuO)2In(_-O-t-Bu)2In(t-Bu2-_-diketonate)2, which has four- and six-coordinate indium centers and virtual C2 symmetry. The t-amoxide complex [In(OCMe2Et)3]2 and oxygen were used as precursors to deposit transparent, highly conductive indium oxide films on silicon, glass, and quartz substrates at substrate temperatures of 300-500 ¡C in a low-pressure chemical vapor deposition process. A backscattering spectrum indicated the film deposited at 500 ¡C was stoichiometric In2O3 (O/In = 1.46±0.07). The films were transparent in the visible region (>75%) and had resistivities as low as 9.1 x 10-4 ½ cm. X-Ray diffraction studies indicated the films deposited on glass were cubic and highly (100) oriented.

A New Luminescent Organic-Inorganic Hybrid Compound with Large Optical Nonlinearity
A.M. Guloy* and Z. Tang
Department of Chemistry
University of Houston, Houston, Texas 77204-5641

P.B. Miranda and V.I. Srdanov*
Department of Chemistry and Institute for Polymers and Organic Solids University of California, Santa Barbara, Santa Barbara CA 93106
A new hybrid compound consisting of inorganic [PbI3] chains coupled by coulomb forces to layers of hyperpolarizable organic cations has been synthesized. In contrast to the herring-bone alignment of the organic chromophores found in similar salts, the crystal structure of this compound features complete alignment of the N-methyl-stilbazolium cations along one crystallographic direction. The second order NLO coefficient, low-dimensional organic-inorganic hybrid exceeds that of KTP by more than one order of magnitude. When pumped by infrared (1064 nm) pulses, most of the generated second-harmonic is absorbed and re-emitted as a bright red fluorescence centered at 620 nm. A possible application of this compound for a novel up-conversion laser is considered. The synergism exhibited between the polarizable inorganic polymers and hyperpolarizable organic molecules adds an important handle for tailoring new materials for nonlinear optical applications.

Impedance Studies of Oxygen Exchange on Dense Thin Film Electrodes of La0.5Sr0.5CoO3-x
Y. L. Yang*, C. L. Chen, S. Y. Chen, C. W. Chu, and A. J. Jacobson
Solid state electrochemical cells with dense oriented thin film electrodes of La0.5Sr0.5CoO3-x (LSCO) were prepared on (100) surfaces of single crystal yttria stabilized zirconia (YSZ) by the pulsed laser deposition (PLD) technique. Oxygen exchange at the electrodes was studied with AC impedance spectroscopy under various temperature and oxygen partial pressure conditions. Three distinctive features were observed in the impedance spectra from high to low frequency corresponding to contributions from the ionic conduction of the YSZ electrolyte, charge transfer at the LSCO/YSZ interface, and the oxygen exchange on the LSCO electrode surface. An equivalent circuit model of the electrode process is used to fit the impedance data. The time constant for the oxygen surface exchange and the interfacial resistance were derived from the from the impedance simulations as a function of temperature and pO2. The results demonstrate the utility of thin film approaches for fundamental studies of electrode behavior.

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A X-ray diffraction determination of the (100) surface termination of a LaAlO3 single crystal
R. Francis and S.C.Moss*
LaAlO3 is a perovskite oxide extensively used as a substrate for thin film growth. Observations by Rabalais et al. suggested a reversible change in the surface stoichiometry of LaAlO3 between room temperature and 250¡C, but no direct structural information was available. We have studied the surface structure of LaAlO3 using crystal truncation rod (CTR) analysis, a technique capable of providing such information. Figure 1a) shows the observed and calculated 00l CTR profiles for (001) oriented single crystals of LaAlO3 at room temperature, together with a structural model of the surface layers corresponding to the calculated profile. Figure 1b) shows the observed and calculated data and the corresponding structural model at ca. 400¡C. At room temperature a fairly minor structural rearrangement of surface layers (relative to the perfectly cut surface) occurs, mostly involving movement of the oxygen atoms out of the surface layer and a concomitant (although smaller) movement of the aluminum atom into the bulk. At high temperature there is a much more radical structural change. In particular, the aluminum atoms in the surface move a considerable distance into the bulk (0.18 of a unit cell) changing from a five coordinated position to a pseudo-tetrahedral site. This is accompanied by other fairly substantial movements of the oxygen atoms in the top two surface layers. The lanthanum atom does not move much, although a small movement towards the surface can clearly be discerned from the CTR data. This change is found to be fully reversible; on changing back to room temperature the structural reconstruction reverses and the surface structure reverts to its previous state