论文标题
钠离子导体中的非谐晶格动力学
Anharmonic Lattice Dynamics in Sodium Ion Conductors
论文作者
论文摘要
我们采用THZ范围依赖温度依赖的拉曼光谱和第一原理晶格 - 动态计算，以表明未息的钠离子导体Na $ _3 $ _3 $ ps $ _4 $和ISOSSTRUCTURAL NA $ _3 $ _3 $ _4 PSE $ _4 $都展示了Anharmonic lattice lattice lattice Dynepics。化合物中的非谐波效应涉及耦合的宿主晶格 - Na $^+$ $离子动力学，在两种情况下都可以驱动四方到立方体相变，但在过渡的非谐性特征上都有质量差异。 na $ _3 $ pse $ _4 $显示几乎纯粹的位移特征，随着对称模式的变化将这些模式转移到拉曼不活跃的布里群区边界，软模式在立方阶段消失。 NA $ _3 $ ps $ _4 $而不是在立方阶段显示订单 - 划分字符，软模式通过相转换持续存在，并在立方阶段中保持在拉曼的活动，违反了该阶段的拉曼选择规则。我们的发现突出了耦合宿主晶格的重要作用 - 移动离子动力学在振动不稳定性中与这些NA $^+$ $离子导体中出色的电导率相吻合。
We employ THz-range temperature-dependent Raman spectroscopy and first-principles lattice-dynamical calculations to show that the undoped sodium ion conductors Na$_3$PS$_4$ and isostructural Na$_3$PSe$_4$ both exhibit anharmonic lattice dynamics. The anharmonic effects in the compounds involve coupled host lattice -- Na$^+$ ion dynamics that drive the tetragonal-to-cubic phase transition in both cases, but with a qualitative difference in the anharmonic character of the transition. Na$_3$PSe$_4$ shows almost purely displacive character with the soft modes disappearing in the cubic phase as the change of symmetry shifts these modes to the Raman-inactive Brillouin zone boundary. Na$_3$PS$_4$ instead shows order-disorder character in the cubic phase, with the soft modes persisting through the phase transition and remaining active in Raman in the cubic phase, violating Raman selection rules for that phase. Our findings highlight the important role of coupled host lattice -- mobile ion dynamics in vibrational instabilities that are coincident with the exceptional conductivity in these Na$^+$ ion conductors.
