Epitaxial growth of Bi$_2$Pt$_2$O$_7$ pyrochlore

TL;DR

This paper reports the first successful epitaxial growth of Bi$_2$Pt$_2$O$_7$ pyrochlore films via annealing of pulsed laser deposited precursor films, advancing the development of oxygen catalyst materials.

Contribution

It demonstrates a novel annealing method to synthesize epitaxial Bi$_2$Pt$_2$O$_7$ pyrochlore films, overcoming previous oxidation challenges.

Findings

First epitaxial Bi$_2$Pt$_2$O$_7$ films achieved

Visualization of pyrochlore structure via electron microscopy

Ordered cation vacancies observed in bismuth-rich films

Abstract

Certain pyrochlore oxides are among the best oxygen catalysts in alkaline media. Hence, exploring epitaxial films of these materials is of great fundamental and technological interest. Unfortunately, direct film growth of one of the most promising pyrochlores, Bi$_2$Pt$_2$O$_7$, has not yet been achieved, owing to the difficulty of oxidizing platinum metal in the precursor material to Pt$^{4+}$. In this work, in order to induce oxidation of the platinum, we annealed pulsed laser deposited films consisting of epitaxial $\delta$-Bi$_2$O$_3$ and co-deposited, comparatively disordered platinum. We present synchrotron x-ray diffraction results that show the annealed films are the first epitaxial crystals of Bi$_2$Pt$_2$O$_7$. We also visualized the pyrochlore structure by scanning transmission electron microscopy, and observed ordered cation vacancies in a bismuth-rich film but not in a platinum-rich film. The similarity between the $\delta$-Bi$_2$O$_3$ and Bi$_2$Pt$_2$O$_7$ structures appears to facilitate the pyrochlore formation. These results constitute a new approach for synthesis of novel pyrochlore thin film oxygen catalysts.