The Sluggish Diffusion of Cations in CeO₂ Probed through Molecular Dynamics and Metadynamics Simulations

Abstract

Cation diffusion in fluorite‐structured CeO2, though far slower than anion diffusion, is an important, high‐temperature process because it governs diverse fabrication and degradation phenomena. Herein, cation diffusion is studied by means of classical molecular dynamics and metadynamics simulations. Three different mechanisms are examined: migration involving an isolated cerium vacancy, migration involving a cerium vacancy in a defect associate with an oxygen vacancy, and migration involving a cation divacancy. For each mechanism, defect diffusion coefficients are calculated as a function of temperature, from which the respective activation enthalpy of defect migration is obtained. Through comparisons with experimental cation diffusion data (specifically, of the absolute magnitude of the cation diffusivity as well as its activation enthalpy), it is concluded that cation diffusion takes place predominantly neither by isolated vacancies nor by cation vacancy–oxygen vacancy associates but by cation divacancies.

Impact of Sr-Containing Secondary Phases on Oxide Conductivity in Solid-Oxide Electrolyzer Cells

“…Barriers are largest for Gd (without V O ) and Ce (with V O ), suggesting that these cations will diffuse relatively slowly; however, they are also immediately adjacent to the GDC–YSZ interface, so they may participate in interfacial reactions regardless. Our results for Ce diffusion agree well with prior computational studies. , La has significantly larger barriers than Sr (roughly 0.8 eV higher), suggesting that its diffusion through GDC will be much slower.…”

“…Our results for Ce diffusion agree well with prior computational studies. 60,61 La has significantly larger barriers than Sr (roughly 0.8 eV higher), suggesting that its diffusion through GDC will be much slower.…”