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arXiv · 1808.06076

Oxygen vacancy-induced structural evolution of SrFeO$_{3-x}$ epitaxial thin film from brownmillerite to perovskite

Seulki Roh·Seokbae Lee·Myounghoon Lee·Yu-Seong Seo·Amit Khare·Taesup Yoo·Sungmin Woo·Woo Seok Choi·Jungseek Hwang·A. Glamazda·K. -Y. Choi
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Abstract

We investigated SrFeO$_{3-x}$ thin films on a SrTiO$_3$ (001) substrate prepared via pulsed laser epitaxy using an optical spectroscopy technique. The oxygen vacancy level ($x$) was controlled by post-annealing processes at different oxygen partial pressures. We achieved a brownmillerite(BM) structure at $x =$ 0.5 and observed the evolution of the crystal structure from BM into perovskite(PV) as the oxygen concentration increased. We observed the evolution of infrared-active phonons with respect to the oxygen concentration, which was closely related to the structural evolution observed via X-ray diffraction. We identified the phonons using the shell-model calculation. Furthermore, we studied temperature-dependent behaviors of the phonon modes of three representative samples: PV, and two BMs (BM$_{\mathrm{oop}}$ and BM$_{\mathrm{ip}}$) with different orientations of the oxygen vacancy channel. In the BM$_{\mathrm{oop}}$ sample, we observed a phonon mode, which exhibited an unusual red-shift with decreasing temperature; this behavior may have been due to the apical oxygen instability in the FeO$_6$ octahedron. Our results provide important information regarding the ionic conduction mechanism in SrFeO$_{3-x}$ material systems.

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Seulki Roh, Seokbae Lee, Myounghoon Lee, Yu-Seong Seo, Amit Khare, Taesup Yoo, Sungmin Woo, Woo Seok Choi, Jungseek Hwang, A. Glamazda, K. -Y. Choi. 2018-08-18. Oxygen vacancy-induced structural evolution of SrFeO$_{3-x}$ epitaxial thin film from brownmillerite to perovskite. https://doi.org/10.1103/physrevb.97.075104

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