A computational study of yttria-stabilized zirconia: II. Cation diffusion

TitleA computational study of yttria-stabilized zirconia: II. Cation diffusion
Publication TypeJournal Article
Year of Publication2017
AuthorsDong, Y, Qi, L, Li, J, Chen, I-W
JournalActa Materialia
Volume126
Pagination438 - 450
Date Published2017/03//
ISBN Number1359-6454
KeywordsAtomistic simulations, creep, cubic zirconia, diffusion, Fast oxygen conductor, mechanism, molecular-dynamics, Point defects, polymorphs, simulation, single-crystals, transport, x-ray-absorption, Yttria-stabilized zirconia, zr-96
Abstract

Cubic yttria-stabilized zirconia is widely used in industrial electrochemical devices. While its fast oxygen ion diffusion is well understood, why cation diffusion is much slower its activation energy (similar to 5 eV) is 10 times that of anion diffusion remains a mystery. Indeed, all previous computational studies predicted more than 5 eV is needed for forming a cation defect, and another 5 eV for moving one. In contrast, our ab initio calculations have correctly predicted the experimentally observed cation diffusivity. We found Schottky pairs are the dominant defects that provide cation vacancies, and their local environments and migrating path are dictated by packing preferences. As a cation exchanges position with a neighboring vacancy, it passes by an empty interstitial site and severely displaces two oxygen neighbors with shortened Zr-O distances. This causes a short-range repulsion against the migrating cation and a longrange disturbance of the surrounding, which explains why cation diffusion is relatively difficult. In comparison, cubic zirconia's migrating oxygen only minimally disturbs neighboring Zr, which explains why it is a fast oxygen conductor. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Short TitleActa Mater.