Topotactic Metal–Insulator Transition in Epitaxial SrFeOx Thin Films

• DOI: 10.1002/adma.201606566
• Publication Date: 2017-07-31T07:23:00Z
• Authors: Amit Khare; Dongwon Shin; Tae Sup Yoo; Minu Kim; Tae Dong Kang; Jaekwang Lee; Seulki Roh; In‐Ho Jung; Jungseek Hwang; Sung Wng Kim; Tae Won Noh; Hiromichi Ohta; Woo Seok Choi
• Keywords: 02 engineering and technology; 0210 nano-technology

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.