Ion migration in Na_0.5Bi_0.5TiO₃ (NBT) was investigated by molecular dynamics (MD) simulations and molecular static (MS) simulations. In MD simulations (>10⁴ ions), performed for simulation times of t_sim = 0.3 ns and at simulation temperatures in the range 1200 ≤ T/K ≤ 2400, oxide ions exhibited appreciable diffusivity, with derived activation enthalpies lower than 0.8 eV, whereas sodium and bismuth cations displayed no diffusion at the temperatures and on the time scale of the simulations. MS calculations yielded high activation barriers (>2 eV) for the migration of these cations. These results strongly suggest that the contribution of A-site cations to the total ionic conductivity is negligible. Bismuth vacancies and sodium vacancies were found to be detrimental to the rate of oxygen diffusion. The effect of ordered arrangements of Bi³⁺/Na⁺ cations on oxygen tracer diffusion was also examined by MD simulations. The (111)-ordered structure was seen to display higher rates of oxygen diffusion than the (100)- and (110)-ordered structures. MS calculations of the individual barriers for oxygen-ion jumps provided insights into this behavior. Our simulation results thus suggest design rules for developing superior low-temperature oxide ion conductors based on NBT perovskites and related materials.

中文翻译：

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钛酸铋钠（NBT）材料中离子迁移的原子模拟：向优良的氧化物离子导体迁移†

通过分子动力学（MD）模拟和分子静态（MS）模拟研究了Na _0.5 Bi _0.5 TiO ₃（NBT）中的离子迁移。在MD模拟（> 10根⁴离子）中，为了模拟时间执行吨_SIM范围1200 = 0.3纳秒，在模拟温度≤ Ť / K≤2400，氧化物离子表现出明显的扩散率，与衍生活化焓低于0.8电子伏特，而钠和铋阳离子在模拟的温度和时间范围内均未显示扩散。MS计算得出了这些阳离子迁移的高活化势垒（> 2 eV）。这些结果强烈表明A的贡献中心阳离子对总离子电导率的影响可以忽略不计。发现铋空位和钠空位对氧扩散速率有害。还通过MD模拟检查了Bi ³⁺ / Na ⁺阳离子的有序排列对氧示踪剂扩散的影响。与（100）和（110）有序的结构相比，可以看到（111）有序的结构显示出更高的氧扩散速率。MS对氧离子跃迁的各个障碍的计算提供了对此行为的见解。因此，我们的仿真结果提出了基于NBT钙钛矿和相关材料开发优良的低温氧化物离子导体的设计规则。