NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA.
Department of Chemistry, Johns Hopkins University, Baltimore, MD, 21218, USA.
Nat Commun. 2018 Jul 5;9(1):2619. doi: 10.1038/s41467-018-05033-7.
Materials with the pyrochlore/fluorite structure have diverse technological applications, from magnetism to nuclear waste disposal. Here we report the observation of structural instability present in the pyrochlores AZrOO' (A = Pr, La) and YbTiOO', that exists despite ideal stoichiometry, ideal cation-ordering, the absence of lone pair effects, and a lack of magnetic order. Though these materials appear to have good long-range order, local structure probes find displacements, of the order of 0.01 nm, within the pyrochlore framework. The pattern of displacements of the AO' sublattice mimics the entropically-driven fluxional motions characteristic of and well-known in the silica mineral β-cristobalite. The universality of such displacements within the pyrochlore structure adds to the known structural diversity and explains the extreme sensitivity to composition found in quantum spin ices and the lack of ferroelectric behavior in pyrochlores.
具有烧绿石/萤石结构的材料具有从磁性到核废料处理等多种技术应用。在这里，我们报告了在烧绿石 AZrOO'（A = Pr、La）和 YbTiOO'中存在的结构不稳定性的观察结果，尽管存在理想的化学计量比、理想的阳离子有序性、不存在孤对效应以及缺乏磁有序。尽管这些材料似乎具有良好的长程有序性，但局部结构探针发现，在烧绿石框架内存在约 0.01nm 的位移。AO'亚晶格的位移模式模仿了在二氧化硅矿物β-方石英中特征的和众所周知的熵驱动的通量运动。这种位移在烧绿石结构中的普遍性增加了已知的结构多样性，并解释了量子自旋冰中对组成的极端敏感性以及烧绿石中缺乏铁电行为的原因。
