Yttrium‐stabilized zirconia (YSZ) and cerium gadolinium oxide (CGO) thin films were prepared by pulsed laser deposition (PLD) under different ambient pressures and substrate temperatures. The microstructures of the obtained films are compared with existing structural zone models for thin‐film growth. The model developed by Thornton (1974) for metallic sputtered films is applied to the metal oxide films grown by PLD and gives a good description for the growth process and the dependence of the microstructure on deposition temperature and pressure. A map of formed microstructures is compiled as a function of background pressure and substrate temperature, and the conditions to obtain dense or porous films for YSZ and CGO are established. The two materials show the same dependence on temperature and pressure. Higher background pressure yields more porous films and a fully dense structure cannot be achieved for substrate temperatures in the range from room temperature to 800 °C. Of special interest for us was the realization and characterization of dense films processed at low temperature (< 500 °C) for the preparation of free‐standing membranes to be used in a micro solid oxide fuel cell. We could achieve such films by processing at 400 °C in 0.026 mbar of oxygen. In‐plane electric conductivities of the films were measured and correlated with the microstructures.
Four compositions of Ba(1-x)Sr(x)Co(1-y)Fe(y)O(3-delta) were studied for phase, oxygen uptake-release, and transition metal (TM) oxidation states after solid state processing and with in situ heating from 300 to 1273 K in air. X-Ray diffraction showed that all compositions except one had the cubic perovskite structure at all temperatures; that with x, y = 0.2 was a mixture as prepared, becoming predominantly cubic at high temperature. Thermogravimetry showed a reversible oxygen absorption-desorption of approximately +/-1% from 700 to 1273 K. X-Ray absorption and Mössbauer spectroscopy showed a majority TM(3+) valence, with at most 40% TM(4+). Up to a temperature of 1073 K, the TM(4+) was reduced to TM(3+). Further heating of the composition with x, y = 0.2 to 1233 K resulted in the reduction of Co(3+) to Co(2+). Results from room temperature measurements confirm the thermally activated carrier hopping mechanism with charge fluctuations, while the high temperature delocalized carrier conductivity occurs with a small amount of TM reduction and without phase change for the initially cubic samples.
Close inspection of the pre-edge in oxygen near-edge x-ray absorption fine structure spectra of single step, gas phase synthesized titanium oxynitride photocatalysts with 20 nm particle size reveals an additional e g resonance in the VB that went unnoticed in previous TiO 2 anion doping studies. The relative spectral weight of this Ti(3d)-O(2p) hybridized state with respect to and located between the readily established t 2g and e g resonances scales qualitatively with the photocatalytic decomposition power, suggesting that this extra resonance bears co-responsibility for the photocatalytic performance of titanium oxynitrides at visible light wavelengths.
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