Doping- and Strain-Dependent Electrolyte-Gate-Induced Perovskite to Brownmillerite Transformation in Epitaxial La1−xSrxCoO3−δ Films

Vipul Chaturvedi, William M. Postiglione, Rohan D. Chakraborty, Biqiong Yu, Wojciech Tabiś, Sajna Hameed, Nikolaos Biniskos, Andrew Jacobson, Zhan Zhang, Hua Zhou, Martin Greven, Vivian E. Ferry, Chris Leighton

Research output: Contribution to journalArticlepeer-review

Abstract

Much recent attention has focused on the voltage-driven reversible topotactic transformation between the ferromagnetic metallic perovskite (P) SrCoO 3-δ and oxygen-vacancy-ordered antiferromagnetic insulating brownmillerite (BM) SrCoO 2.5. This is emerging as a paradigmatic example of the power of electrochemical gating (using, e.g., ionic liquids/gels), the wide modulation of electronic, magnetic, and optical properties generating clear application potential. SrCoO 3 films are challenging with respect to stability, however, and there has been little exploration of alternate compositions. Here, we present the first study of ion-gel-gating-induced P → BM transformations across almost the entire La 1- x Sr x CoO 3 phase diagram (0 ≤ x ≤ 0.70), under both tensile and compressive epitaxial strain. Electronic transport, magnetometry, and operando synchrotron X-ray diffraction establish that voltage-induced P → BM transformations are possible at essentially all x, including x ≤ 0.50, where both P and BM phases are highly stable. Under small compressive strain, the transformation threshold voltage decreases from approximately +2.7 V at x = 0 to negligible at x = 0.70. Both larger compressive strain and tensile strain induce further threshold voltage lowering, particularly at low x. The P → BM threshold voltage is thus tunable, via both composition and strain. At x = 0.50, voltage-controlled ferromagnetism, transport, and optical transmittance are then demonstrated, achieving Curie temperature and resistivity modulations of ∼220 K and at least 5 orders of magnitude, respectively, and enabling estimation of the voltage-dependent Co valence. The results are analyzed in the context of doping- and strain-dependent oxygen vacancy formation energies and diffusion coefficients, establishing that it is thermodynamic factors, not kinetics, that underpin the decrease in the threshold voltage with x, that is, with increasing formal Co valence. These findings substantially advance the practical and mechanistic understanding of this voltage-driven transformation, with fundamental and technological implications.

Original languageEnglish (US)
Pages (from-to)51205-51217
Number of pages13
JournalACS applied materials & interfaces
Volume13
Issue number43
DOIs
StatePublished - Nov 3 2021

Bibliographical note

Funding Information:
This work was supported primarily by the National Science Foundation through the University of Minnesota MRSEC under award number DMR-2011401. Parts of this work were performed in the Characterization Facility, UMN, which receives partial support from NSF through the MRSEC and NNCI programs. Portions of this work were also conducted in the Minnesota Nano Center, which is supported by NSF through the National Nano Coordinated Infrastructure (NNCI) under ECCS-2025124. Part of this work also used resources of the Advanced Photon Source, a DOE Office of Science User Facility operated by Argonne National Laboratory under contract no. DE-AC02-06CH11357. W.T. acknowledges support from the Polish National Agency for Academic Exchange under the Polish Returns 2019 Program, grant no. PPN/PPO/2019/1/00014, and the subsidy of the Ministry of Science and Higher Education of Poland.

Publisher Copyright:
© 2021 American Chemical Society.

Keywords

  • cobaltites
  • electrolyte gating
  • ionic control of materials
  • perovskite oxides
  • voltage-controlled magnetism

How much support was provided by MRSEC?

  • Primary

PubMed: MeSH publication types

  • Journal Article

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