Modulating the Structure and Magnetic Properties of ε-Fe2O3 Nanoparticles via Electrochemical Li+ Insertion

Sou Yasuhara; Yosuke Hamasaki; Tsukasa Katayama; Takahiro Ao; Yoshiyuki Inaguma; Hajime Hojo; Maarit Karppinen; Anish Philip; Shintaro Yasui; Mitsuru Itoh

doi:10.1021/acs.inorgchem.9b03302

Modulating the Structure and Magnetic Properties of ε-Fe₂O₃ Nanoparticles via Electrochemical Li⁺ Insertion

Inorg Chem. 2020 Apr 6;59(7):4357-4365. doi: 10.1021/acs.inorgchem.9b03302. Epub 2020 Mar 18.

Authors

Affiliations

¹ Laboratory for Materials and Structures, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
² Department of Applied Physics, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan.
³ Department of Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
⁴ Department of Chemistry, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
⁵ Department of Advanced Materials Science and Engineering, Kyushu University, 6-1 Kasuga Koen, Kasuga, Fukuoka 816-8580, Japan.
⁶ Department of Chemistry and Materials Science, Aalto University, FI-00076 Espoo, Finland.

PMID: 32186859
DOI: 10.1021/acs.inorgchem.9b03302

Abstract

ε-Fe₂O₃, a metastable phase of iron oxide, is widely known as a room-temperature multiferroic material or as a superhard magnet. Element substitution into ε-Fe₂O₃ has been reported in the literature; however, the substituted ions have a strong site preference depending on their ionic radii and valence. In this study, in order to characterize the crystal structure and magnetic properties of ε-Fe₂O₃ in the Fe²⁺/Fe³⁺ coexisting states, Li⁺ was electrochemically inserted into ε-Fe₂O₃ to reduce Fe³⁺. The discharge and charge of Li⁺ into/from ε-Fe₂O₃ revealed that Li⁺ insertion was successful. X-ray magnetic circular dichroism results indicated that the reduced Fe did not exhibit site preference. Increasing the Li⁺ content in ε-Fe₂O₃ resulted in decreased saturation magnetization and irregular variation of the coercive field. We present a comprehensive discussion of how magnetic properties are modified with increasing Li⁺ content using transmission electron microscopy images and considering the Li⁺ diffusion coefficient. The results suggest that inserting Li⁺ into crystalline ε-Fe₂O₃ is a useful tool for characterizing crystal structure, lithiation limit, and magnetic properties in the coexistence of Fe²⁺/Fe³⁺.