Bi2Ti2O7和Bi2Ru2O7中的非相干Bi偏心：绝缘体与金属
Incoherent Bi off-centering in Bi2Ti2O7 and Bi2Ru2O7: Insulator versus metal
摘要：
立方、化学计量的氧化物化合物Bi 2 Ti 2 O 6 O '（也写作Bi 2 Ti 2 O 7）和Bi 2 Ru 2 O 6 O'（也写作Bi 2 Ru 2 O 7）在烧绿石A位上具有共同的孤对活性Bi 3+阳离子，具有偏离中心的倾向。与Bi 2 Ti 2 O 6 O '不同，Bi 2 Ru 2 O 6 O'是金属，因此询问导电电子和/或在费米能处的Bi 6s态的参与是否影响Bi 3+位移是有趣的。通过对中子散射的逆蒙特卡罗分析，详细揭示了Bi_2 Ti_2 O_6 O_（60）中Bi ~（3+）的非相干性。Bi_2Ru_2O_6O ′的类似分析也揭示了不相干的偏心，其幅度较小，并且具有明显不同的取向偏好。这里提出的总散射分析表明，Bi在两种化合物中完全是Bi 3+。Bi_2Ti_2O_6O ′中的无序具有稳定化合价的作用，同时为电子孤对提供空间。在Bi_2Ru_2O_6O ′中，偏离中心不需要满足价态，而是由被传导电子部分屏蔽的孤对电子驱动的。
英文摘要：
The cubic, stoichiometric oxide compounds Bi2Ti2O6O' (also written Bi2Ti2O7) and Bi2Ru2O6O' (also written Bi2Ru2O7) have in common lone-pair active Bi3+ cations on the pyrochlore A-site with a propensity to off-center. Unlike Bi2Ti2O6O', Bi2Ru2O6O' is a metal, so it is of interest to ask whether conduction electrons and/or involvement of Bi 6s states at the Fermi energy influence Bi3+ displacements. The Bi3+ off-centering in Bi2Ti2O6O' is incoherent as revealed in detail by reverse Monte Carlo analysis of total neutron scattering. Similar analysis of Bi2Ru2O6O' reveals incoherent off-centering as well, of smaller magnitude and with distinctly different orientational preference. Analysis of total scattering presented here shows that Bi in both compounds is entirely Bi3+. Disorder in Bi2Ti2O6O' has the effect of stabilizing valence while simultaneously providing space for the electronic lone pair. In Bi2Ru2O6O', off-centering is not required to satisfy valence, but is driven by the lone pair which is partially screened by conduction electrons.
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