The Role of Co Valence in Charge Transport in the Entropy-Stabilized Oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O

Valerie Jacobson, Jake Huang, Charles Titus, Rebecca Smaha, Meagan Papac, Sang-Jun Lee, Andriy Zakutayev, Geoff Brennecka

Research output: Contribution to journalArticlepeer-review

4 Scopus Citations

Abstract

Many of the studies on the entropy-stabilized oxide (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O have been heavily application-based. Previous works have studied effects of cation stoichiometry on the entropy-driven reaction to form a single phase, but a fundamental exploration of the effects of anion stoichiometry and/or redox chemistry on electrical properties is lacking. Using near-edge X-ray absorption fine structure (NEXAFS) and electrical measurements, we show that oxidizing thin film samples of (Mg0.2Co0.2Ni0.2Cu0.2Zn0.2)O affects primarily the valence of Co, leaving the other cations in this high-entropy system unchanged. This oxidation increases electrical conduction in these thin films, which occurs via small polaron hopping mediated by the Co valence shift from 2+ to a mixed 2+/3+ state. In parallel, we show that bulk samples sintered in an oxygen-rich atmosphere have a lower activation energy for electrical conduction than those equilibrated in a nitrogen (reducing) atmosphere. Combining feasible defect compensation scenarios with electrical impedance measurements and NEXAFS data, we propose a self-consistent interpretation of Co redox-mediated small polaron conduction as the dominant method of charge transfer in this system.

Original languageAmerican English
Pages (from-to)1531-1539
Number of pages9
JournalJournal of the American Ceramic Society
Volume106
Issue number2
DOIs
StatePublished - 2023

Bibliographical note

Publisher Copyright:
© 2022 The Authors. Journal of the American Ceramic Society published by Wiley Periodicals LLC on behalf of American Ceramic Society.

NREL Publication Number

  • NREL/JA-5K00-83338

Keywords

  • activation energy
  • charge carrier
  • entropy
  • IV
  • NEXAFS
  • XANES
  • XAS

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