Mixed valency in cerium oxide crystallographic phases: Determination of valence of the different cerium sites by the bond valence method

TL;DR

This study uses the bond valence method to analyze cerium oxides, revealing mixed valence states and non-integer valences at various sites, challenging simple stoichiometric predictions.

Contribution

It applies the bond valence method to determine site-specific cerium valences across multiple cerium oxide phases, providing new insights into their electronic structure.

Findings

CeO2 has a mixed-valence ground state with f-electron population of 0.27.

A- and C-sesquioxides have nearly pure f^1 configuration.

Intermediate oxides exhibit non-integral and unexpected valences.

Abstract

We have applied the bond valence method to cerium oxides to determine the oxidation states of the Ce ion at the various site symmetries of the crystals. The crystals studied include cerium dioxide and the two sesquioxides along with some selected intermediate phases which are crystallographically well characterized. Our results indicate that cerium dioxide has a mixed-valence ground state with an f-electron population on the Ce site of 0.27 while both the A- and C-sesquioxides have a nearly pure f^1 configuration. The Ce sites in most of the intermediate oxides have non-integral valences. Furthermore, many of these valences are different from the values predicted from a naive consideration of the stoichiometric valence of the compound.