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Mismatch in cation size causes rapid anion dynamics in solid electrolytes: the role of the Arrhenius pre-factor†
Dalton Transactions ( IF 3.5 ) Pub Date : 2018-02-21 00:00:00 , DOI: 10.1039/c7dt04487a Stefan Breuer 1, 2, 3, 4 , Martin Wilkening 1, 2, 3, 4, 5
Dalton Transactions ( IF 3.5 ) Pub Date : 2018-02-21 00:00:00 , DOI: 10.1039/c7dt04487a Stefan Breuer 1, 2, 3, 4 , Martin Wilkening 1, 2, 3, 4, 5
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Crystalline ion conductors exhibiting fast ion dynamics are of utmost importance for the development of, e.g., sensors or rechargeable batteries. In some layer-structured or nanostructured compounds fluorine ions participate in remarkably fast self-diffusion processes. As has been shown earlier, F ion dynamics in nanocrystalline, defect-rich BaF2 is much higher than that in the coarse-grained counterpart BaF2. The thermally metastable fluoride (Ba,Ca)F2, which can be prepared by joint high-energy ball milling of the binary fluorides, exhibits even better ion transport properties. While long-range ion dynamics has been studied recently, less information is known about local ion hopping processes to which 19F nuclear magnetic resonance (NMR) spin–lattice relaxation is sensitive. The present paper aims at understanding ion dynamics in metastable, nanocrystalline (Ba,Ca)F2 by correlating short-range ion hopping with long-range transport properties. Variable-temperature NMR line shapes clearly indicate fast and slow F spin reservoirs. Surprisingly, from an atomic-scale point of view increased ion dynamics at intermediate values of composition is reflected by increased absolute spin–lattice relaxation rates rather than by a distinct minimum in activation energy. Hence, the pre-factor of the underlying Arrhenius relation, which is determined by the number of mobile spins, the attempt frequency and entropy effects, is identified as the parameter that directly enhances short-range ion dynamics in metastable (Ba,Ca)F2. Concerted ion migration could also play an important role to explain the anomalies seen in NMR spin–lattice relaxation.
中文翻译：
阳离子尺寸不匹配会导致固体电解质中快速的阴离子动力学：Arrhenius前置因子的作用†
表现出快速离子动力学的结晶离子导体对于例如传感器或可再充电电池的开发至关重要。在某些层结构或纳米结构的化合物中，氟离子显着参与了快速的自扩散过程。如前所述，纳米晶，富含缺陷的BaF 2中的F离子动力学比粗晶的BaF 2中的F离子动力学高得多。可以通过对二元氟化物进行联合高能球磨制备的热亚稳态氟化物（Ba，Ca）F 2表现出更好的离子传输性能。尽管最近已研究了远程离子动力学，但有关局部离子跳跃过程的信息知之甚少，19F核磁共振（NMR）自旋晶格弛豫很敏感。本文旨在通过将短程离子跳跃与长程传输特性相关联，了解亚稳态纳米晶（Ba，Ca）F 2中的离子动力学。可变温度NMR线形清楚表明快速和慢速F自旋储层。出人意料的是，从原子尺度的角度来看，在中间组成值时增加的离子动力学是通过增加的自旋-晶格弛豫速率来反映的，而不是通过活化能的明显最小值来反映的。因此，由移动自旋的数量，尝试频率和熵效应确定的潜在阿累尼乌斯关系的前置因子被确定为直接增强亚稳（Ba，Ca）F中短程离子动力学的参数。2。协同的离子迁移也可能在解释NMR自旋晶格弛豫中发现的异常中起重要作用。
更新日期：2018-02-21
中文翻译：
阳离子尺寸不匹配会导致固体电解质中快速的阴离子动力学：Arrhenius前置因子的作用†
表现出快速离子动力学的结晶离子导体对于例如传感器或可再充电电池的开发至关重要。在某些层结构或纳米结构的化合物中，氟离子显着参与了快速的自扩散过程。如前所述，纳米晶，富含缺陷的BaF 2中的F离子动力学比粗晶的BaF 2中的F离子动力学高得多。可以通过对二元氟化物进行联合高能球磨制备的热亚稳态氟化物（Ba，Ca）F 2表现出更好的离子传输性能。尽管最近已研究了远程离子动力学，但有关局部离子跳跃过程的信息知之甚少，19F核磁共振（NMR）自旋晶格弛豫很敏感。本文旨在通过将短程离子跳跃与长程传输特性相关联，了解亚稳态纳米晶（Ba，Ca）F 2中的离子动力学。可变温度NMR线形清楚表明快速和慢速F自旋储层。出人意料的是，从原子尺度的角度来看，在中间组成值时增加的离子动力学是通过增加的自旋-晶格弛豫速率来反映的，而不是通过活化能的明显最小值来反映的。因此，由移动自旋的数量，尝试频率和熵效应确定的潜在阿累尼乌斯关系的前置因子被确定为直接增强亚稳（Ba，Ca）F中短程离子动力学的参数。2。协同的离子迁移也可能在解释NMR自旋晶格弛豫中发现的异常中起重要作用。
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