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

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.

6 pages, 7 figures

References in corpus (5)

• Local structural origins of the distinct electronic properties of Nb-substituted SrTiO${}_3$ and BaTi$O_3$
• Lone pairs in insulating pyrochlores: Ice rules and high-$k$ behavior
• Large Low Temperature Specific Heat in Pyrochlore Bi${}_2$Ti${}_2$O${}_7$
• Atomic displacements in the "charge-ice" pyrochlore Bi2Ti2O7 studied by neutron total scattering
• Frustrated Ferroelectricity in Niobate Pyrochlores

Cited by in corpus (5)

• Frustrated quantum rare-earth pyrochlores
• Synthesis, floating zone crystal growth and characterization of the Quantum Spin Ice $\mathrm{P}{\mathrm{r}}_2\mathrm{Z}{\mathrm{r}}_2{\mathrm{O}}_7$ pyrochlore
• Structural disorder, magnetism, and electrical and thermoelectric properties of pyrochlore Nd2Ru2O7
• Quadrupolar Singlet Ground State of Praseodymium in a Modulated Pyrochlore
• Disorder and Quantum spin ice