Reverse Monte Carlo neutron scattering study of the "ordered-ice" oxide pyrochlore Pb2Ru2O6.5

TL;DR

This study uses neutron scattering and reverse Monte Carlo simulations to analyze the detailed crystal structure of Pb2Ru2O6.5, revealing complete vacancy and oxygen ion ordering and comparing its properties with related pyrochlores.

Contribution

It provides a detailed, unbiased structural analysis of Pb2Ru2O6.5, highlighting its vacancy and oxygen ordering and linking structural features with electronic and thermal properties.

Findings

Vacancy and O' ion are fully ordered.

The structure fits the F43m space group.

Low-temperature heat capacity is compared with related pyrochlores.

Abstract

We employ high-resolution total neutron scattering in conjunction with reverse Monte Carlo simulations to examine, in a detailed and unbiased manner, the crystal structure of the vacancy-ordered oxide pyrochlore Pb2Ru2O6.5 in light of its structural analogy with proton-ordering in the structures of ice. We find that the vacancy and the O' ion are completely ordered, and that the average structure in the F43m space group describes the vacancy ordering precisely. We complement these results with an examination of the Pb2+ lone pair network using density functional electronic structure calculations, and a comparison of the low-temperature lattice-only heat capacity of Pb2Ru2O6.5 with that of other related pyrochlores.