Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides,Journal of the American Chemical Society

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Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-12-22 , DOI: 10.1021/jacs.0c10739
Bo Jiang , Craig A. Bridges , Raymond R. Unocic , Krishna Chaitanya Pitike , Valentino R. Cooper , Yuanpeng Zhang , De-Ye Lin _{1,

2} , Katharine Page ₃

Affiliation

High-entropy oxides (HEOs) have attracted great interest in diverse fields because of their inherent opportunities to tailor and combine materials functionalities. The control of local order/disorder in the class is by extension a grand challenge toward realizing their vast potential. Here we report the first examples of pyrochlore HEOs with five M-site cations, for Nd2M2O7, in which the local structure has been investigated by neutron diffraction and pair distribution function (PDF) analysis. The average structure of the pyrochlores is found to be orthorhombic Imma, in agreement with radius-ratio rules governing the structural archetype. The computed PDFs from density functional theory relaxed special quasirandom structure models are compared with real space PDFs in this work to evaluate M-site order/disorder. Reverse Monte Carlo combined with ab initio molecular dynamics and Metropolis Monte Carlo simulations demonstrates that Nd2(Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2)2O7 is synthesized with its M-site local to nanoscale order highly randomized/disordered, while Nd2(Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2)2O7+x exhibits a strong distortion of the TiO6 octahedron and small degree of Ti chemical short-range order (SRO) on the subnanometer scale. Calculations suggest that this may be intrinsic, energetically favored SRO rather than due to sample processing. These results offer an important demonstration that the engineered variation of participating ions in HEOs, even among those with very similar radii, provides richly diverse opportunities to control local order/disorder motifs-and therefore materials properties for future designs. This work also hints at the exquisite level of detail that may be needed in computational and experimental data analysis to guide structure-property tuning in the emerging HEO materials class.

中文翻译：

烧绿石高熵氧化物局部无序和畸变的探讨

高熵氧化物 (HEO) 因其固有的定制和组合材料功能的机会而引起了各个领域的极大兴趣。控制班级中的局部秩序/混乱是实现其巨大潜力的巨大挑战。在这里，我们报告了 Nd2M2O7 具有五个 M 位阳离子的烧绿石 HEO 的第一个例子，其中已通过中子衍射和对分布函数 (PDF) 分析研究了局部结构。发现烧绿石的平均结构是斜方晶伊玛，与控制结构原型的半径比规则一致。在这项工作中，将密度泛函理论计算的 PDF 松弛特殊拟随机结构模型与真实空间 PDF 进行比较，以评估 M 位点有序/无序。反向蒙特卡罗结合 ab initio 分子动力学和 Metropolis Monte Carlo 模拟表明，Nd2 (Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2) 2O7 是合成的，其 M 位点局部至纳米级有序高度随机/无序，而 Nd2 ( Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2) 2O7 + x 在亚纳米尺度上表现出 TiO6 八面体的强烈畸变和小程度的 Ti 化学短程有序 (SRO)。计算表明，这可能是内在的、精力充沛的 SRO，而不是由于样品处理。这些结果提供了一个重要的证明，即 HEO 中参与离子的工程变化，即使在那些具有非常相似半径的离子中，也提供了丰富多样的机会来控制局部有序/无序图案，从而为未来设计提供材料特性。

更新日期：2020-12-22

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