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Collective diffusion within the superionic regime of Bi_2O_3

机译：Bi_2O_3的超离子状态下的集体扩散

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The δ phase of Bi_2O_3 has the highest known value of oxide ion conductivity within the solid state and, therefore, remains a benchmark for the development of future generations of electrolyte materials to fuel-cell technologies. Conventionally, the high value of conductivity in δ-Bi_2O_3 has been explained by a large concentration of inherent vacancies together with a strongly polarizable Bi-O bond. We show from ab initio molecular dynamics simulations that short "chains" of collective migrating oxygens also contribute strongly to the high value of conductivity with the single-particle Nernst-Einstein (N.E.) conductivity to collective (dc) conductivity σ~(N.E.)/σ~~(dc) ~ 0.57 ± 0.05 at 1033 K. The nature of collective events is investigated from a hopping model, the distinct part of the van Hove function and from the extent of dynamical heterogeneities in the superionc regime. Results from this analysis indicate that the main contribution to collective ionic diffusion in δ-Bi_2O_3 involves short collinear chains of two or three oxygens. These chains are either initiated by an oxygen that jumps into an already occupied oxygen cavity (where they coexist for a very short time before the residential oxygen is kicked out of its cavity) or from a jump into a vacant cavity which triggers a next-nearest-neighboring oxygen to migrate. Since δ-Bi_2O_3 is easily stabilized in a range of environments, the nature of these collective chains can give important insight into the design of δ-Bi_2O_3-based fuel cells for the future.
机译：Bi_2O_3的δ相在固态状态下具有最高的氧化物离子电导率已知值，因此仍然是开发下一代燃料电池用电解质材料的基准。常规上，δ-Bi_2O_3的高电导率值是由大量的固有空位以及强烈极化的Bi-O键共同解释的。我们从头算分子动力学模拟表明，集体迁移氧的短“链”也对单电能斯特-爱因斯坦（NE）电导率达到集体（dc）电导率σ〜（NE）/在1033 K时σ〜（dc）〜0.57±0.05。从跳跃模型，van Hove函数的不同部分以及超离子体系中的动力学异质性的范围研究了集体事件的性质。分析的结果表明，对δ-Bi_2O_3中的集体离子扩散的主要贡献涉及两个或三个氧的短共线链。这些链是由跳入已经占据的氧气腔中的氧气引发的（它们在共存的居民氧气被踢出腔之前的很短时间内共存），或者是由于跳入一个空的腔而引发下一个最近的氧气-邻近的氧气迁移。由于δ-Bi_2O_3在各种环境中都很容易稳定，因此这些集合链的性质可以为将来基于δ-Bi_2O_3的燃料电池的设计提供重要的见识。

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  • 来源
    《Physical review》 |2020年第10期|104309.1-104309.7|共7页
  • 作者

    Chris E. Mohn; Marcin Krynski;

  • 作者单位

    Centre for Earth Evolution and Dynamics University of Oslo N-0315 Oslo Norway;

    Department of Chemistry University of Cambridge Cambridge CB2 1EW United Kingdom;

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