Modulated structure determination and ion transport mechanism of oxide-ion conductor CeNbO4+\u03b4

Jian Li,Jianhua Lin,Shipeng Geng,Xiaojun Kuang,Cong Lin,Fengjuan Pan,Junliang Sun,Mathieu Allix,Lukas Palatinus

doi:10.1038/s41467-020-18481-x

Abstract

CeNbO4+δ, a family of oxygen hyperstoichiometry materials with varying oxygen content (CeNbO4, CeNbO4.08, CeNbO4.25, CeNbO4.33) that shows mixed electronic and oxide ionic conduction, has been known for four decades. However, the oxide ionic transport mechanism has remained unclear due to the unknown atomic structures of CeNbO4.08 and CeNbO4.33. Here, we report the complex (3 + 1)D incommensurately modulated structure of CeNbO4.08, and the supercell structure of CeNbO4.33 from single nanocrystals by using a three-dimensional electron diffraction technique. Two oxide ion migration events are identified in CeNbO4.08 and CeNbO4.25 by molecular dynamics simulations, which was a synergic-cooperation knock-on mechanism involving continuous breaking and reformation of Nb2O9 units. However, the excess oxygen in CeNbO4.33 hardly migrates because of the high concentration and the ordered distribution of the excess oxide ions. The relationship between the structure and oxide ion migration for the whole series of CeNbO4+δ compounds elucidated here provides a direction for the performance optimization of these compounds.

Highlights

CeNbO4+δ, a family of oxygen hyperstoichiometry materials with varying oxygen content (CeNbO4, CeNbO4.08, CeNbO4.25, CeNbO4.33) that shows mixed electronic and oxide ionic conduction, has been known for four decades
The relationship between the structure and oxide ion migration for the whole series of CeNbO4+δ compounds here provides means to optimize the performance of these compounds and to develop better oxygen hyperstoichiometric materials for a wide variety of applications
The oxygen contents of the phases were analyzed by thermogravimetric analysis (TGA), which yields formulae CeNbO4.11(2), CeNbO4.24(2), and CeNbO4.33(1) (Supplementary Fig. 2)

Summary

Introduction

CeNbO4+δ, a family of oxygen hyperstoichiometry materials with varying oxygen content (CeNbO4, CeNbO4.08, CeNbO4.25, CeNbO4.33) that shows mixed electronic and oxide ionic conduction, has been known for four decades. The discovery of the series of 114 cobaltites ((Ln,Ca)1BaCo4O7) revealed the existence of closely related structures with various crystallographic symmetries and the possibility of oxygen nonstoichiometry in the range “O7”–“O8.5” in those systems, which opened up a new field for the investigation of strongly correlated electron systems This change of oxygen stoichiometry, which induces the variation of the Co2+:Co3+ ratio in the system, is expected to influence the physical properties of these compounds considerably. The relationship between the structure and oxide ion migration for the whole series of CeNbO4+δ compounds here provides means to optimize the performance of these compounds and to develop better oxygen hyperstoichiometric materials for a wide variety of applications

Methods

Results

Conclusion