Yuichi Shimakawa

Abstract:

Oxygen ions are incorporated in and released from transition-metal oxides when the valence states of the transition-metal ions change [1]. In topotactic changes of perovskite-structure oxides like SrFe²⁺O₂ - SrFe³⁺O_2.5 - SrFe⁴⁺O₃, we found that the oxygen incorporation and release behaviors are strongly influenced by the structural factors. The A-site disordered perovskite (La_1/3Ca_2/3)FeO₃ with unusually high valance Fe^3.67+ releases oxygen gradually above 500°C, whereas the A-site-layer-ordered perovskite LaCa₂Fe₃O₉ with the identical chemical composition of (La_1/3Ca_2/3)FeO₃ readily releases oxygen around 400°C [2,3]. From the B-site-layer-ordered double perovskite Ca₂FeMnO₆ with Mn⁴⁺ and unusual high valence Fe⁴⁺, oxygen is released only form the two-dimensional Fe-O layers according to the successive changes of Ca₂Fe⁴⁺Mn⁴⁺O₆ - Ca₂Fe^3.5+Mn⁴⁺O_5.75 - Ca₂Fe³⁺Mn⁴⁺O_5.5. The B-site-disordered Ca₂(FeMn)O₆, on the other hand, oxygen appears to be released at about 390°C by a single change of Ca₂(Fe⁴⁺Mn⁴⁺)O₆ - Ca₂(Fe³⁺Mn⁴⁺)O_5.5 [4,5]. Thus, the oxygen release behaviors differ depending on both A-site and B-site cation order. An important point for the behaviors of oxides with unusually high valence cations like Fe⁴⁺ is that the incorporation and the release of oxygen can occur at much lower temperatures than those with typical valence transition-metal ions. We will discuss the details of such behaviors from temperature-dependent structure analysis.

[1] Y. Shimakawa, Bull. Chem. Soc. Jpn. 86, 299-311 (2013).
[2] H. Guo, Y. Hosaka, H. Seki, T. Saito, N. Ichikawa, and Y. Shimakawa, J. Solid State Chem. 246, 199-202 (2017).
[3] H. Guo, Y. Hosaka, F. D. Romero, T. Saito, N. Ichikawa, and Y. Shimakawa, Inorg. Chem. 56, 3695-3701 (2017).
[4] Y. Hosaka, N. Ichikawa, T. Saito, P. Manuel, D. Khalyavin, J. Paul Attfield, and Y. Shimakawa, J. Am. Chem. Soc. 137, 7468-7473 (2015).
[5] H. Hosaka, N. Ichikawa, T. Saito, J. P. Attfield, and Y. Shimakawa, Phys. Rev. B 94, 104429 (2016).