Compositional Influence of Local and Long-Range Polarity in the Frustrated Pyrochlore System Bi 2−x RE xTi 2 O 7 ( RE = Y 3+ , Ho 3+ )
Compositional Influence of Local and Long-Range Polarity in the Frustrated Pyrochlore System Bi 2−x RE xTi 2 O 7 ( RE = Y 3+ , Ho 3+ )
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受阻烧绿石系统中局部和远程极性的成分影响 Bi 2âx RE xTi 2 O 7 (RE = Y 3 , Ho 3 )
DOI：
10.1039/d2tc01328b
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发表时间：
2022
影响因子：
6.4
通讯作者：
Laurita, Geneva
中科院分区：
文献类型：
--
作者：
Bailey, Owen;Husremovic, Samra;Murphy, Madison;Ross, Jason;Gong, Joyce;Olds, Daniel;Laurita, Geneva
由于烧绿石晶格上阳离子的三角形排列，结构扭曲（例如阳离子偏心）在烧绿石结构中受到抑制。这种几何约束抑制了大多数烧绿石氧化物材料从顺电相到铁电相的转变。很少有烧绿石材料能够克服这种挫败感并表现出极性晶体结构，而解开这种结构的起源有助于理解复杂材料中的极性。在此，我们假设通过在 A 位掺杂不具有立体化学活性孤电子对的稀土阳离子，可以缓解烧绿石晶格上的挫败现象。为了评估挫败感是否得到缓解，我们通过中子和 X 射线总散射分析了各种 Bi2−xRExTi2O7 (RE = Y, Ho) 烧绿石中的阳离子偏心。受烧绿石文献中已知扭曲的启发，我们提出了我们的发现，即大多数样品显示出与 β-方英石结构相似的局部扭曲。我们还评论了在结构行为中发挥作用的因素的复杂性，包括阳离子大小、键价、电子结构和磁电相互作用。我们认为，在烧绿石晶格上添加磁性阳离子可能在延长 Bi-Ho 系列电偶极子的实空间相关长度方面发挥作用，并为驱动烧绿石晶格上的长程极性提供考虑。
Structural distortions such as cation off-centering are frustrated in the pyrochlore structure due to the triangular arrangement of cations on the pyrochlore lattice. This geometric constraint inhibits a transition from a paraelectric to a ferroelectric phase in the majority of pyrochlore oxide materials. Few pyrochlore materials can overcome this frustration and exhibit polar crystal structures, and unraveling the origin of such leads to the understanding of polarity in complex materials. Herein we hypothesize that frustration on the pyrochlore lattice can be relieved through A-site doping with rare earth cations that do not possess stereochemically active lone pairs. To assess if frustration is relieved, we have analyzed cation off-centering in various Bi2−xRExTi2O7 (RE = Y, Ho) pyrochlores through neutron and X-ray total scattering. Motivated by known distortions from the pyrochlore literature, we present our findings that most samples show local distortions similar to the β-cristobalite structure. We additionally comment on the complexity of factors that play a role in the structural behavior, including cation size, bond valence, electronic structure, and magnetoelectric interactions. We posit that the addition of magnetic cations on the pyrochlore lattice may play a role in an extension of the real-space correlation length of electric dipoles in the Bi-Ho series, and offer considerations for driving long-range polarity on the pyrochlore lattice.