Issue 4, 2018

Formation of defects and their effects on hydride ion transport properties in a series of K2NiF4-type oxyhydrides

Abstract

Several K2NiF4-type oxyhydrides (La2−xySrx+yLiH1−x+yO3−y) have in recent years been shown to exhibit significant transport of hydride ions. The migration mechanism of hydride ion conduction is, however, still not understood. In the following contribution, we explore the formation and stability of defects and the hydride ion migration mechanisms in three fast hydride ion conducting K2NiF4-type oxyhydrides (La2LiHO3, LaSrLiH2O2 and Sr2LiH3O) based on first principles calculations. Our results demonstrate that Image ID:c7ta08435h-t1.gif and Image ID:c7ta08435h-t2.gif are the dominant defects, coexistent with minor amounts of Image ID:c7ta08435h-t3.gif. Both Image ID:c7ta08435h-t4.gif and Image ID:c7ta08435h-t5.gif exhibit strong site preference at the axial sites of the LiX6 octahedron, showing that hydride ion transport is strongly anisotropic in the crystal lattice. Hydride ions migrate through a vacancy-mediated mechanism with calculated migration enthalpies varying from 0.21 to 0.45 eV depending on the composition of the oxyhydrides. By mapping all relevant minimum energy pathways for hydride and oxygen ions, we reveal that the transport of hydride ions in La2LiHO3 is inhibited by slow oxygen ion (vacancy) migration. For LaSrLiH2O2 and Sr2LiH3O, Image ID:c7ta08435h-t6.gif and Image ID:c7ta08435h-t7.gif defect associates inhibit the hydride ion conduction further due to the strong binding energies of the complexes. However, the structural and compositional flexibility of K2NiF4-type oxyhydrides gives advantages for enhancing the hydride ion conductivity, for instance by introducing acceptor dopants on cation sites to create more vacant sites.

Graphical abstract: Formation of defects and their effects on hydride ion transport properties in a series of K2NiF4-type oxyhydrides

Article information

Article type
Paper
Submitted
23 Sep 2017
Accepted
18 Nov 2017
First published
18 Nov 2017

J. Mater. Chem. A, 2018,6, 1454-1461

Formation of defects and their effects on hydride ion transport properties in a series of K2NiF4-type oxyhydrides

X. Liu, T. S. Bjørheim and R. Haugsrud, J. Mater. Chem. A, 2018, 6, 1454 DOI: 10.1039/C7TA08435H

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements