Thin-film solid-oxide fuel cells (TF-SOFCs) fabricated using microelectromechanical systems (MEMS) processing techniques not only help lower the cell operating temperature but also provide a convenient platform for studying cathodic losses. Utilizing these platforms, cathode kinetics can be enhanced dramatically by engineering the microstructure of the cathode/electrolyte interface by increasing the surface grain-boundary density. Nanoscale secondary ion mass spectrometry and high-resolution transmission electron microscopy studies have shown that oxygen exchange at electrolyte surface grain boundaries is facilitated by a high population of oxide-ion vacancies segregating preferentially to the grain boundaries. Furthermore, three-dimensional structuring of TF-SOFCs enabled by various lithography methods also helps increase the active surface area and enhance the surface exchange reaction. Although their practical prospects are yet to be verified, MEMS-based TF-SOFC platforms hold the potential to provide high-performance for low-temperature SOFC applications.

Proton conductivity of yttrium-doped barium zirconate grown on MgO(100) using pulsed laser deposition (PLD) has been explored as a function of film thickness (60∼670nm) related to crystal and grain structure in the nano scale. Highly textured thin film (60nm) without significant grain separation showed high ionic conductivity close to the bulk BYZ value while thick polycrystalline samples showed lower values with clear grain and grain boundary formation.

The stability of BaFe12O19 and BaFe2O4 was studied by the oxygen coulometric titration technique between 700 °C and 1000 °C using a solid-state electrochemical cell. This temperature range is technologically important for the deposition of BaFe2O19 magnetic thin films. The thermodynamic information obtained from the titration measurements was corroborated with structural identification of phases prepared under electrochemically controlled conditions. Accordingly, a section of the Ba–Fe–O ternary phase diagram around the BaFe12O19 composition was constructed in this temperature range. The standard Gibbs free energy change for the decomposition of BaFe12O19 into BaFe2O4, Fe3O4, and O2 is given by the expression ΔG°[J/mol] = 7.23 × 105 −480T. In the oxygen pressure-temperature domain, the thermodynamic stability limits of BaFe12O19 and BaFe2O4 are given by the expressions In[Po2(atm)] = 69.37 −1.04 × 105 T−1 and In[Po2(atm)] = 27.68 −7.12 × 104 T−1, respectively. The stability limits determined here help define the process conditions for the successful synthesis of these phases.

This paper reports the findings of a phase-equilibrium study of the Y-Ba-Cu-O quaternary system in which the oxygen activity was monitored and controlled by a solid-state ionic technique. A stabilized zirconia electrolyte was used to titrate oxygen in or out of the sample and to monitor the oxygen activity inside a sealed sample chamber.

Compositions at or near YBa2Cu3Ox were studied at elevated temperatures in a wide range of oxygen pressures. All compositions indicated the presence of an invariant polyphase reaction- e.g., at 1 × 10-3 atm of oxygen pressure at 850 °C-- below which the superconducting phase becomes thermodynamically unstable and undergoes a decomposition reaction. Complementary x-ray diffraction analysis of samples prepared under well-defined oxygen pressures identified the phases present and, along with the oxygen coulometric titration data, allowed the construction of a portion of the relevant quarternary phase diagram.