We report investigation of phonons and oxygen diffusion in Bi2O3 and (Bi0.7Y0.3)2O3. The phonon spectra have been measured in Bi2O3 at high temperatures up to 1083 K using inelastic neutron scattering. Ab-initio calculations have been used to compute the individual contributions of the constituent atoms in Bi2O3 and (Bi0.7Y0.3)2O3 to the total phonon density of states. Our computed results indicate that as temperature is increased, there is a complete loss of sharp peak structure in the vibrational density of states. Ab-initio molecular dynamics simulations show that even at 1000 K in δ-phase Bi2O3, Bi-Bi correlations remain ordered in the crystalline lattice while the correlations between O-O show liquid like disordered behavior. In the case of (Bi0.7Y0.3)2O3, the O-O correlations broadened at around 500 K indicating that oxygen conductivity is possible at such low temperatures in (Bi0.7Y0.3)2O3 although the conductivity is much less than that observed in the undoped high temperature δ-phase of Bi2O3. This result is consistent with the calculated diffusion coefficients of oxygen and observation by QENS experiments. Our ab-initio molecular dynamics calculations predict that macroscopic diffusion is attainable in (Bi0.7Y0.3)2O3 at much lower temperatures, which is more suited for technological applications. Our studies elucidate the easy directions of diffusion in δ-Bi2O3 and (Bi0.7Y0.3)2O3.

中文翻译：

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Bi2O3 和 (Bi0.7Y0.3)2O3 中的声子和氧扩散


我们报告了 Bi2O3 和 (Bi0.7Y0.3)2O3 中声子和氧扩散的研究。使用非弹性中子散射在高达 1083 K 的高温下测量了 Bi2O3 的声子光谱。从头计算已用于计算 Bi2O3 和 (Bi0.7Y0.3)2O3 中的组成原子对总声子态密度的单独贡献。我们的计算结果表明，随着温度升高，态振动密度中的尖峰结构完全丧失。从头算分子动力学模拟表明，即使在 1000 K 的 δ 相 Bi2O3 中，Bi-Bi 相关性在晶格中仍保持有序，而 OO 之间的相关性则表现出类似液体的无序行为。对于 (Bi0.7Y0.3)2O3，OO 相关性在 500 K 左右变宽，表明 (Bi0.7Y0.3)2O3 在如此低的温度下氧电导率是可能的，尽管电导率远低于在 (Bi0.7Y0.3)2O3 中观察到的电导率Bi2O3 的未掺杂高温δ相。该结果与计算的氧扩散系数和QENS实验观察结果一致。我们的从头算分子动力学计算预测，(Bi0.7Y0.3)2O3 可以在更低的温度下实现宏观扩散，这更适合技术应用。我们的研究阐明了 δ-Bi2O3 和 (Bi0.7Y0.3)2O3 中容易扩散的方向。