Fast ion conductivity in strained defect-fluorite structure created by ion tracks in Gd2Ti2O7.

Dilpuneet S Aidhy,Yanwen Zhang,William J Weber,Matthew F Chisholm,Ritesh Sachan,Olli Pakarinen,Eva Zarkadoula

doi:10.1038/srep16297

Abstract

The structure and ion-conducting properties of the defect-fluorite ring structure formed around amorphous ion-tracks by swift heavy ion irradiation of Gd2Ti2O7 pyrochlore are investigated. High angle annular dark field imaging complemented with ion-track molecular dynamics simulations show that the atoms in the ring structure are disordered, and have relatively larger cation-cation interspacing than in the bulk pyrochlore, illustrating the presence of tensile strain in the ring region. Density functional theory calculations show that the non-equilibrium defect-fluorite structure can be stabilized by tensile strain. The pyrochlore to defect-fluorite structure transformation in the ring region is predicted to be induced by recrystallization during a melt-quench process and stabilized by tensile strain. Static pair-potential calculations show that planar tensile strain lowers oxygen vacancy migration barriers in pyrochlores, in agreement with recent studies on fluorite and perovskite materials. In view of these results, it is suggested that strain engineering could be simultaneously used to stabilize the defect-fluorite structure and gain control over its high ion-conducting properties.

Highlights

Heavy 2.2 GeV Au ions, to investigate associated strain in the ring region
We show that cation disorder leads to high oxygen diffusivity compared to ordered pyrochlore structure
In view of the many recent reports of enhancing oxygen diffusivity via tensile strain induced by heterointerfacing[15,16], using density functional theory (DFT) calculations, we show that the high conducting defect-fluorite structure can be stabilized via tensile strain, and predict that oxygen diffusivity can be strain-enhanced by synthesizing pyrochlores as defect-fluorites via ion tracks or as thin-films

Summary

Introduction

Heavy 2.2 GeV Au ions, to investigate associated strain in the ring region. We use molecular dynamics (MD) simulations to model ion tracks to complement the experimental observations. In view of the many recent reports of enhancing oxygen diffusivity via tensile strain induced by heterointerfacing[15,16], using density functional theory (DFT) calculations, we show that the high conducting defect-fluorite structure can be stabilized via tensile strain, and predict that oxygen diffusivity can be strain-enhanced by synthesizing pyrochlores as defect-fluorites via ion tracks or as thin-films. This realization that control over the defect-fluorite structure can be possibly gained via tensile strain opens up new avenues for materials design for fast-ion conductor applications

Methods

Results

Conclusion