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arXiv · 1101.0791

Incoherent Bi off-centering in Bi2Ti2O7 and Bi2Ru2O7: Insulator versus metal

Daniel P. Shoemaker·Ram Seshadri·Makoto Tachibana·Andrew L. Hector
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Abstract

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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Daniel P. Shoemaker, Ram Seshadri, Makoto Tachibana, Andrew L. Hector. 2011-06-09. Incoherent Bi off-centering in Bi2Ti2O7 and Bi2Ru2O7: Insulator versus metal. https://doi.org/10.1103/physrevb.84.064117

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