Cooperative Oxide-Ion Transport in Pyrochlore Y2Ti2O7: A First-Principles Molecular Dynamics Study
Cooperative Oxide-Ion Transport in Pyrochlore Y2Ti2O7: A First-Principles Molecular Dynamics Study
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DOI：
10.1021/acs.jpcc.1c03610
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
Ushio Matsumoto;T. Ogawa;C. Fisher;S. Kitaoka;I. Tanaka
中科院分区：
文献类型：
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作者：
Ushio Matsumoto;T. Ogawa;C. Fisher;S. Kitaoka;I. Tanaka
我们发展了一种基于Voronoi-Dirichlet划分的分析局部结构单元时间序列数据的映射方法，以量化在第一性原理分子动力学模拟中观察到的焦绿石Y2Ti2O7(空间群：FD3̅m)中的缺陷态和氧离子迁移机制。缺陷态分为三种类型：Frenkel对、单空位和分裂空位。虽然能量上最有利的缺陷类型在低温下是分裂空位，但在高温下分裂空位和单一空位同样有利。氧离子的迁移是通过裂解空位的两步协同机制进行的。爬像微调弹性带计算表明，合作扩散机制的能垒(0.65 eV)比简单的分步机制(0.96 eV)要小得多。这种较低的势垒与文献中报道的Y2Ti2O7中氧离子扩散的实验激活能相当，使得这种以前未被认识的合作机制最有可能使氧离子在钛酸盐焦绿石中传输。
We developed a mapping approach for analyzing time-series data of local structural units based on the Voronoi–Dirichlet partition to quantify the defect states and oxide-ion migration mechanism in pyrochlore Y2Ti2O7(space group:Fd3̅m) observed during first-principles molecular dynamics simulations. Defect states are classified into three types: a Frenkel pair, a single vacancy, and a split vacancy. Although the energetically most favorable defect type is a split vacancy at low temperatures, split and single vacancies are found to be equally favorable at high temperatures. Oxide-ion migration occurs by a two-step cooperative mechanism via a split vacancy. Climbing-image nudged elastic band calculations show the energy barrier for the cooperative diffusion mechanism (0.65 eV) to be substantially less than that of a simple stepwise mechanism (0.96 eV). This lower-energy barrier is comparable to experimental activation energies of oxide-ion diffusion in Y2Ti2O7reported in the literature, making this previously unrecognized cooperative mechanism the most likely candidate for enabling oxide-ion transport in the titanate pyrochlore.