Local structure and its implications for the relaxor ferroelectric Cd2Nb2O7
Local structure and its implications for the relaxor ferroelectric Cd2Nb2O7
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局域结构及其对弛豫铁电体 Cd2Nb2O7 的影响
DOI：
10.1103/physrevresearch.4.033187
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发表时间：
2022
影响因子：
4.2
通讯作者：
Rondinelli, James M.
中科院分区：
文献类型：
--
作者：
Hickox-Young, Daniel;Laurita, Geneva;Meier, Quintin N.;Olds, Daniel;Spaldin, Nicola A.;Norman, Michael R.;Rondinelli, James M.
弛豫铁电转变被认为是通过二中心声子模式的异常凝聚来描述的。然而，事实证明，它们各自的作用是模糊的，支持主要模式的初始研究和指向相反模式的全局晶体精炼之间存在分歧。在这里，我们通过 X 射线对分布函数测量来证明局部占主导地位，但全局占主导地位，从而解决了这个问题。这种行为与我们自己的实验室初始模拟中发现的与这两种畸变模式相关的能量表面的近简并性一致。我们的第一性原理计算还表明，这些能量表面几乎是各向同性的，这为其中发现的众多结构转变及其弛豫行为提供了解释。我们的结果指出了局部结构的几种候选描述，其中一些描述了给定铌四面体内铌位移的二进/二出行为。尽管这表明自旋冰存在电荷类似物的可能性，但我们的结果更符合海森堡对偶极波动的描述，而不是伊辛描述。我们希望这能鼓励未来对 Nb 和 Cd 偶极波动及其相关模式动力学的实验研究。
The relaxor ferroelectric transition inis thought to be described by the unusual condensation of two-centered phonon modes,and. However, their respective roles have proven to be ambiguous, with disagreement betweenab initiostudies, which favoras the primary mode, and global crystal refinements, which point toinstead. Here, we resolve this issue by demonstrating from x-ray pair distribution function measurements that locally,dominates, but globally,dominates. This behavior is consistent with the near degeneracy of the energy surfaces associated with these two distortion modes found in our ownab initiosimulations. Our first-principles calculations also show that these energy surfaces are almost isotropic, providing an explanation for the numerous structural transitions found in, as well as its relaxor behavior. Our results point to several candidate descriptions of the local structure, some of which demonstrate two-in/two-out behavior for Nb displacements within a given Nb tetrahedron. Although this suggests the possibility of a charge analog of spin ice in, our results are more consistent with a Heisenberg-like description for dipolar fluctuations rather than an Ising one. We hope this encourages future experimental investigations of the Nb and Cd dipolar fluctuations, along with their associated mode dynamics.