Lecture: «Epitaxial crystals of Bi2Pt2O7 pyrochlore through the transformation of δ–Bi2O3 fluorite»
Dra Araceli Gutierrez Llorente (Universidad Rey Juan Carlos - Madrid)
CiQUS Seminar Room
12:15 h
Pyrochlore oxides, A2B2O7, that exhibit catalytic activity toward oxygen reduction and mixed ionic-electronic conduction are prospective cathode materials for various types of fuel cells. Specifically, pyrochlore powders have been studied as cathode materials in solid oxide fuel cells. However, epitaxial oxide thin films can have superior properties compared to powders.
On the other hand, there is an increasing interest in epitaxial films of materials with crystal structures different from perovskite, such as pyrochlore, not yet studied in epitaxial form for fuel cell applications. Bi2Pt2O7 pyrochlore is thought to be one of the most promising oxide catalysts for application in fuel cell technology. Unfortunately, direct film growth of Bi2Pt2O7 has not yet been achieved, owing to the difficulty of oxidizing platinum metal in the precursor material to Pt4+.
In this work, in order to induce oxidation of the platinum, we annealed pulsed laser deposited films consisting of epitaxial δ–Bi2O3 and co-deposited, comparatively disordered platinum. We present synchrotron x-ray diffraction results that show the non-uniform annealed films contain the first epitaxial crystals of Bi2Pt2O7. We also visualized the pyrochlore structure by scanning transmission electron microscopy. The similarity between the δ–Bi2O3 and Bi2Pt2O7 structures appears to facilitate the pyrochlore formation. These results provide the only route to date for the formation of epitaxial Bi2Pt2O7.