Effects of state filling and localization on chemical expansion in praseodymium-oxide perovskites
Effects of state filling and localization on chemical expansion in praseodymium-oxide perovskites
复制标题
态填充和局域化对氧化镨钙钛矿化学膨胀的影响
DOI：
10.1039/d2ta06756k
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发表时间：
2023
影响因子：
11.9
通讯作者：
Ertekin, Elif
中科院分区：
文献类型：
--
作者：
Yong, Adrian Xiao;Anderson, Lawrence O.;Perry, Nicola H.;Ertekin, Elif
在氧化物材料中，氧空位浓度的增加通常导致晶格膨胀，这是一种称为化学膨胀的现象，可以引入有害应力并导致潜在的器件故障。材料的化学膨胀中经常涉及的一个因素是多价阳离子电子态的局部化程度。当从晶格中除去氧并形成空位时，据信两个释放的电子还原多价阳离子并使晶格膨胀，其中更局部化的阳离子状态导致更大的膨胀。在这项工作中，我们通过计算和实验研究了两种具有超低化学膨胀的Pr基钙钛矿PrGa 1 − xMgxO 3 −δ和BaPr 1 − xYxO 3 −δ及其母体化合物PrGaO 3 −δ和BaPrO 3 −δ的化学膨胀。利用密度泛函理论，Pr-4f电子的局域化程度通过调节Hubbard U参数来改变。我们发现Pr-4f电子局域化和化学膨胀之间的关系表现出比以前建立的更复杂。这种关系取决于两个电子所填充的状态的性质，这可能不一定涉及Pr的还原。如果Pr的还原是不利的，则可以形成F′中心缺陷，从而导致较小的化学膨胀。如果空穴态存在于材料中，则由电子填充的状态可以是Pr-4f和/或O-2 p空穴态，这取决于Pr-4f局域化的程度。O-2 p空穴比Pr-4f空穴更离域，导致O-2 p空穴被填充时的化学膨胀较小。X射线光电子能谱显示PrGa0.9Mg0.1O3−δ和BaPr0.9Y0.1O3−δ中的Pr 4+浓度较低，支持O-2 p空穴在这些材料所表现出的低化学膨胀中的可能作用。这项工作突出了电子局域化对化学膨胀的重要影响，特别是当存在空穴态时，指出了调整材料化学膨胀的设计策略。
In oxide materials, an increase in oxygen vacancy concentration often results in lattice expansion, a phenomenon known as chemical expansion that can introduce detrimental stresses and lead to potential device failure. One factor often implicated in the chemical expansion of materials is the degree of localization of the multivalent cation electronic states. When an oxygen is removed from the lattice and a vacancy forms, it is believed that the two released electrons reduce multivalent cations and expand the lattice, with more localized cation states resulting in larger expansion. In this work, we computationally and experimentally studied the chemical expansion of two Pr-based perovskites that exhibit ultra-low chemical expansion, PrGa1−xMgxO3−δ and BaPr1−xYxO3−δ, and their parent compounds PrGaO3−δ and BaPrO3−δ. Using density functional theory, the degree of localization of the Pr-4f electrons was varied by adjusting the Hubbard U parameter. We find that the relationship between Pr-4f electron localization and chemical expansion exhibits more complexity than previously established. This relationship depends on the nature of the states filled by the two electrons, which may not necessarily involve the reduction of Pr. F′-center defects can form if the reduction of Pr is unfavorable, leading to smaller chemical expansions. If hole states are present in the material, the states filled by the electrons can be Pr-4f and/or O-2p hole states depending on the degree of Pr-4f localization. The O-2p holes are more delocalized than the Pr-4f holes, resulting in smaller chemical expansions when the O-2p holes are filled. X-ray photoelectron spectroscopy reveals low concentrations of Pr4+ in PrGa0.9Mg0.1O3−δ and BaPr0.9Y0.1O3−δ, supporting the possible role of O-2p holes in the low chemical expansions exhibited by these materials. This work highlights the non-trivial effects of electron localization on chemical expansion, particularly when hole states are present, pointing to design strategies to tune the chemical expansion of materials.