5 years ago

Topotactic Metal–Insulator Transition in Epitaxial SrFeOx Thin Films

Topotactic Metal–Insulator Transition in Epitaxial SrFeOx Thin Films
Tae Dong Kang, In-Ho Jung, Amit Khare, Tae Won Noh, Seulki Roh, Jungseek Hwang, Dongwon Shin, Woo Seok Choi, Sung Wng Kim, Jaekwang Lee, Minu Kim, Hiromichi Ohta, Tae Sup Yoo
Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeOx epitaxial thin films is identified in real-time, during the progress of reversible topotactic phase transformation. Using real-time optical spectroscopy, the phase transition between the two structurally distinct phases (i.e., brownmillerite and perovskite) is quantitatively monitored, and a pressure–temperature phase diagram of the topotactic transformation is constructed for the first time. The transformation at relatively low temperatures is attributed to a markedly small difference in Gibbs free energy compared to the known similar class of materials to date. This study highlights the phase stability and reversibility of SrFeOx thin films, which is highly relevant for energy and environmental applications exploiting the redox reactions. Topotactic phase transformation coupled with metal–insulator transition in SrFeOx epitaxial thin films is studied using real-time optical spectroscopy. The oxygen-content-dependent phase transition leads to a pressure–temperature phase diagram of the topotactic transformation. The transformation at relatively low temperatures is ascribed to a markedly small Gibbs free energy difference between the two structurally distinctive phases.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201606566

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