Jahn–Teller-driven phase segregation in MnxCo3−xO4 spinel thin films
Jahn–Teller-driven phase segregation in MnxCo3−xO4 spinel thin films
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DOI：
10.1116/6.0002329
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发表时间：
2022-10
期刊：
影响因子：
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通讯作者：
Miles D. Blanchet;B. Matthews;S. Spurgeon;S. Heald;T. Isaacs-smith;R. Comes
中科院分区：
文献类型：
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作者：
Miles D. Blanchet;B. Matthews;S. Spurgeon;S. Heald;T. Isaacs-smith;R. Comes
由富含稀土的锰和钴组成的过渡金属尖晶石氧化物长期以来一直被探索用于催化反应和储能。然而，由于样品制备和材料的最终结构特性的不同，理解功能特性可能是具有挑战性的。外延薄膜合成提供了一种新的方法来生产精确控制的材料，以探索文献中报道的变化。本工作采用分子束外延技术合成了x=0到x=1.28的MnxCo3-−xO4样品，并对其进行了表征，得到了材料性能随化学计量比变化的曲线。用原位X射线光电子能谱、X射线衍射仪、扫描电子显微镜和偏振K边X射线吸收光谱对薄膜进行了表征。在此范围内的Mn离子被发现是八面体配位的，符合反尖晶石结构。样品主要表现为Mn3+和Mn4+混合的特征，随着Mn3+含量的增加和Mn3+形式电荷的增加，样品有明显的相分离倾向。相分离可能是由于分别与Mn4+和Jahn-Teller活性Mn3+八面体有关的立方和四方晶体结构之间的结构不相容造成的。我们的结果有助于解释这些用于可再生能源技术的有希望的材料在样本之间的报道差异。
Transition metal spinel oxides comprised of earth-abundant Mn and Co have long been explored for their use in catalytic reactions and energy storage. However, understanding functional properties can be challenging due to differences in sample preparation and the ultimate structural properties of the materials. Epitaxial thin film synthesis provides a novel means of producing precisely controlled materials to explore the variations reported in the literature. In this work, MnxCo3−xO4 samples from x = 0 to x = 1.28 were synthesized through molecular beam epitaxy and characterized to develop a material properties map as a function of stoichiometry. Films were characterized via in situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, and polarized K-edge x-ray absorption spectroscopy. Mn cations within this range were found to be octahedrally coordinated, in line with an inverse spinel structure. Samples largely show mixed Mn3+ and Mn4+ character with evidence of phase segregation tendencies with the increasing Mn content and increasing Mn3+ formal charge. Phase segregation may occur due to structural incompatibility between cubic and tetragonal crystal structures associated with Mn4+ and Jahn–Teller active Mn3+ octahedra, respectively. Our results help in explaining the reported differences across samples in these promising materials for renewable energy technologies.