The role of Co valence in charge transport in the entropy‐stabilized oxide (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O
The role of Co valence in charge transport in the entropy‐stabilized oxide (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O
复制标题
Co 价态在熵稳定氧化物 (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O 中电荷传输中的作用
DOI：
10.1111/jace.18820
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发表时间：
2022
影响因子：
3.9
通讯作者：
Brennecka, G. L.
中科院分区：
文献类型：
--
作者：
Jacobson, V.;Huang, J.;Titus, C. J.;Smaha, R. W.;Papac, M.;Lee, S. J.;Zakutayev, A.;Brennecka, G. L.
许多关于熵稳定氧化物（Mg0.2Co0.2Ni0.2Cu0.2Zn0.2）O的研究都是基于应用的。先前的工作已经研究了阳离子化学计量对熵驱动反应以形成单相的影响，但是缺乏对阴离子化学计量和/或氧化还原化学对电性质的影响的基本探索。使用近边X射线吸收精细结构（NEXAFS）和电学测量，我们发现氧化薄膜样品（Mg0.2Co0.2Ni0.2Cu0.2Zn0.2）O主要影响Co的价态，而这个高熵系统中的其他阳离子不变。这种氧化增加了这些薄膜中的导电性，这是通过由Co从2+到混合2+/3+状态的价态位移介导的小极化子跳跃而发生的。同时，我们表明，在富氧气氛中烧结的大块样品比在氮（还原）气氛中平衡的样品具有更低的导电活化能。将可行的缺陷补偿方案与电阻抗测量和NEXAFS数据相结合，我们提出了一个自洽的解释，即Co氧化还原介导的小极化子传导是该系统中电荷转移的主要方法。
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.