Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case.
Combined Role of Biaxial Strain and Nonstoichiometry for the Electronic, Magnetic, and Redox Properties of Lithiated Metal-Oxide Films: The LiMn2O4 Case.
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DOI：
10.1021/acsami.1c18326
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发表时间：
2021-11
影响因子：
9.5
通讯作者：
I. Scivetti;G. Teobaldi
中科院分区：
文献类型：
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作者：
I. Scivetti;G. Teobaldi
了解LiMn2O4薄膜的电子、磁性和氧化还原特性的应变和非化学计量之间的相互作用，对于其作为锂离子电池（LIB）阴极、光电极、可持续自旋电子学应用系统以及结合这些技术的新兴应用的发展至关重要。密度泛函理论（DFT）模拟表明，压缩应变通过诱导价带边缘bbbb10 eV的上移，增加了（111）LiMn2O4薄膜的还原驱动。DFT结果表明，无论LiMn2O4薄膜的晶体取向如何，双轴膨胀都增加了Mn原子的磁矩。相反，双轴压缩减少了它们。对于铁磁薄膜，这些变化可能是实质性的，在模拟应变范围内（从-6到+3%），每个单元细胞的变化可超过4玻尔磁子。DFT模拟还揭示了一种补偿机制，即应变诱导Mn和O原子的磁矩发生相反的变化，从而导致铁磁薄膜的整体磁矩恒定。计算出的应变引起的原子磁矩变化反映了Mn和O原子的局部电子杂化的变化，这反过来表明应变可调的局部化学和电化学反应性。一些能量有利的（110）和（111）铁磁表面被证明是半金属的，少数自旋带隙高达3.2 eV，并且与自旋相关的电子输运和可能的自旋相关的电化学和电催化性质相容。铁磁性半金属态对表面非化学计量和成分变化的弹性，促使人们探索LiMn2O4薄膜在最先进的稀土金属基铁磁性半金属氧化物之外的可持续自旋电子应用的潜力。
Understanding the interplay between strain and nonstoichiometry for the electronic, magnetic, and redox properties of LiMn2O4 films is essential for their development as Li-ion battery (LIB) cathodes, photoelectrodes, and systems for sustainable spintronics applications as well as for emerging applications that combine these technologies. Here, density functional theory (DFT) simulations suggest that compressive strain increases the reduction drive of (111) LiMn2O4 films by inducing >1 eV upshift of the valence band edge. The DFT results indicate that, regardless of the crystallographic orientation for the LiMn2O4 film, biaxial expansion increases the magnetic moments of the Mn atoms. Conversely, biaxial compression reduces them. For ferromagnetic films, these changes can be substantial and as large as over 4 Bohr magnetons per unit cell over the simulated range of strain (from -6 to +3%). The DFT simulations also uncover a compensation mechanism whereby strain induces opposite changes in the magnetic moment of the Mn and O atoms, leading to an overall constant magnetic moment for the ferromagnetic films. The calculated strain-induced changes in atomic magnetic moments reflect modifications in the local electronic hybridization of both the Mn and O atoms, which in turn suggests strain-tunable, local chemical, and electrochemical reactivity. Several energy-favored (110) and (111) ferromagnetic surfaces turn out to be half-metallic with minority-spin band gaps as large as 3.2 eV and compatible with spin-dependent electron-transport and possible spin-dependent electrochemical and electrocatalytic properties. The resilience of the ferromagnetic, half-metallic states to surface nonstoichiometry and compositional changes invites exploration of the potential of LiMn2O4 thin films for sustainable spintronic applications beyond state-of-the-art, rare-earth metal-based, ferromagnetic half-metallic oxides.