Preishuber-Pflügl F, Bottke P, Pregartner V, Bitschnau B, Wilkening M
Institute for Chemistry and Technology of Materials, and Christian Doppler Laboratory for Lithium Batteries, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria.
Phys Chem Chem Phys. 2014 May 28;16(20):9580-90. doi: 10.1039/c4cp00422a.
Chemical reactions induced by mechanical treatment may give access to new compounds whose properties are governed by chemical metastability, defects introduced and the size effects present. Their interplay may lead to nanocrystalline ceramics with enhanced transport properties being useful to act as solid electrolytes. Here, the introduction of large amounts of La into the cubic structure of BaF2 served as such an example. The ion transport properties in terms of dc-conductivity values of the F(-) anion conductor Ba1-xLaxF2+x (here with x = 0.4) considerably exceed those of pure, nanocrystalline BaF2. So far, there is only little knowledge about activation energies and jump rates of the elementary hopping processes. Here, we took advantage of both impedance spectroscopy and (19)F NMR relaxometry to get to the bottom of ion jump diffusion proceeding on short-range and long-range length scales in Ba0.6La0.4F2.4. While macroscopic transport is governed by an activation energy of 0.55 to 0.59 eV, the elementary steps of hopping seen by NMR are characterised by much smaller activation energies. Fortunately, we were able to deduce an F(-) self-diffusion coefficient by the application of spin-locking NMR relaxometry.
机械处理引发的化学反应可能会产生新的化合物，其性质由化学亚稳性、引入的缺陷以及存在的尺寸效应所决定。它们之间的相互作用可能导致具有增强传输性能的纳米晶陶瓷，可作为固体电解质。在此，向BaF₂的立方结构中引入大量La就是这样一个例子。F⁻阴离子导体Ba₁₋ₓLaₓF₂₊ₓ（此处x = 0.4）的直流电导率值所体现的离子传输性能大大超过了纯纳米晶BaF₂。到目前为止，关于基本跳跃过程的活化能和跳跃速率的知识还很少。在此，我们利用阻抗谱和¹⁹F NMR弛豫测量法来深入了解Ba₀.₆La₀.₄F₂.₄中短程和长程尺度上的离子跳跃扩散。虽然宏观传输由0.55至0.59 eV的活化能控制，但NMR观察到的跳跃基本步骤的特征是活化能要小得多。幸运的是，通过应用自旋锁定NMR弛豫测量法，我们能够推导出F⁻自扩散系数。
