Is Geometric Frustration-Induced Disorder a Recipe for High Ionic Conductivity?
Is Geometric Frustration-Induced Disorder a Recipe for High Ionic Conductivity?
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DOI：
10.1021/jacs.7b00502
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发表时间：
2017-04-26
影响因子：
15
通讯作者：
Sayle, Dean C.
中科院分区：
文献类型：
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作者：
Duevel, Andre;Heitjans, Paul;Sayle, Dean C.
离子电导率在许多重要的工业应用中无处不在，如燃料电池、电池、传感器和催化。因此，这些系统的导电性可调是其商业可行性的关键。在这里，我们表明几何挫折可以被利用作为电导率调谐的载体。特别是，我们对一个原型系统CaF2施加几何挫折，通过与BaF2球磨，产生纳米结构的Ba1-xCaxF2固溶体，并将其离子电导率提高了5个数量级以上。通过将每个实验与MD模拟相镜像，包括“模拟合成”，我们揭示了几何挫折赋予系统在环境温度下的结构和动力学属性，这些属性通常与将材料加热到其超电子转变温度以上有关。这包括结构紊乱、体积过剩、赝空位阵列和集体输运机制；我们证明了Ba1-xCaxF2体系的多余体积与离子电导率相关。我们还提供了几何挫折诱导电导率是一种普遍现象的证据，这可能有助于解释掺杂萤石结构氧化物（如铈和氧化锆）中的高离子电导率，并应用于固体氧化物燃料电池。一篇关于几何挫折的综述[Nature 2015, 521, 303]指出，经典晶体学不足以描述具有相关无序的系统，但相关无序具有清晰的晶体学特征。在这里，我们确定了几何挫折的两种可能的晶体学特征：过量体积和相关的“蛇形”离子输运；后者推断出相关紊乱。特别是，当链中的一个离子移动时，链中所有其他（相关的）离子同时移动。关键的是，我们的模拟揭示了蛇形链，长度超过40 A，这表明我们的无序系统中存在长期相关性。同样，玻璃材料中的集体输运也有很好的记录[例如，J. Chem。物理学报，2013,38(2):538 - 538。可能的晶体学命名法，用于描述无序系统中的长程有序，可能包括，例如，“蛇”阵列的形状、长度和分支。这样的表征可能最终提供在无序、无定形或液态的远程有序和离子电导率、熔化和结晶等过程之间的洞察力和差异。
Ionic conductivity is ubiquitous to many industrially important applications such as fuel cells, batteries, sensors, and catalysis. Tunable conductivity in these systems is therefore key to their commercial viability. Here, we show that geometric frustration can be exploited as a vehicle for conductivity tuning. In particular, we imposed geometric frustration upon a prototypical system, CaF2, by ball milling it with BaF2, to create nanostructured Ba1-xCaxF2 solid solutions and increased its ionic conductivity by over 5 orders of magnitude. By mirroring each experiment with MD simulation, including "simulating synthesis", we reveal that geometric frustration confers, on a system at ambient temperature, structural and dynamical attributes that are typically associated with heating a material above its superionic transition temperature. These include structural disorder, excess volume, pseudovacancy arrays, and collective transport mechanisms; we show that the excess volume correlates with ionic conductivity for the Ba1-xCaxF2 system. We also present evidence that geometric frustration-induced conductivity is a general phenomenon, which may help explain the high ionic conductivity in doped fluorite-structured oxides such as ceria and zirconia, with application for solid oxide fuel cells. A review on geometric frustration [Nature 2015, 521, 303] remarks that classical crystallography is inadequate to describe systems with correlated disorder, but that correlated disorder has clear crystallographic signatures. Here, we identify two possible crystallographic signatures of geometric frustration: excess volume and correlated "snake-like" ionic transport; the latter infers correlated disorder. In particular, as one ion in the chain moves, all the other (correlated) ions in the chain move simultaneously. Critically, our simulations reveal snake-like chains, over 40 A in length, which indicates long-range correlation in our disordered systems. Similarly, collective transport in glassy materials is well documented [for example, J. Chem. Phys. 2013, 138, 12A.538]. Possible crystallographic nomenclatures, to be used to describe long-range order in disordered systems, may include, for example, the shape, length, and branching of the "snake" arrays. Such characterizations may ultimately provide insight and differences between long-range order in disordered, amorphous, or liquid states and processes such as ionic conductivity, melting, and crystallization.