Oxygen Diffusion in Yttria‐Stabilized Zirconia: A New Simulation Model

Abstract

We present a multiscale modeling approach to study oxygen diffusion in cubic yttria‐stabilized zirconia. In this approach, we employ density functional theory methods to calculate activation energies for oxygen migration in different cation environments. These are used in a kinetic Monte Carlo framework to calculate long‐time oxygen diffusivities. Simulation results show that the oxygen diffusivity attains a maximum value at around 0.1 mole fraction yttria. This variation in the oxygen diffusivity with yttria mole fraction and the calculated values for the diffusivity agree well with experiment. The competing effects of increased oxygen vacancy concentration and increasing activation energy and correlation effects for oxygen diffusion with increasing yttria mole fraction are responsible for the observed dopant content dependence of the oxygen diffusivity. We provide a detailed analysis of cation‐dopant‐induced correlation effects in support of the above explanation.

The Roles of Classical Molecular Dynamics Simulation in Solid Oxide Fuel Cells

“…Facilitated by increasing temperature, the isolated anion and its vacancy become mobile at T > 800 K. At very high temperatures 1000 K or above, all the YSZ crystals exhibit exceptionally high values of ionic conductivity (σ) and reach the order of 0.1 S cm-1 (Fig. 7), consistent with the range of reported ionic conductivity in experiment (Hull, 2004;Nakamura et al, 1986) at T  1000-1250 K. As an anion-deficient fluorite, the oxygen ion and its vacancy migration kinetics in YSZ crystal, however, cannot be described solely by a simple vacancy assisted diffusion model (Hull, 2004;Krishnamurthy et al, 2004 (Fig. 8) (Casselton, 1970;Hull, 2004;Krishnamurthy et al, 2004).…”

“…7), consistent with the range of reported ionic conductivity in experiment (Hull, 2004;Nakamura et al, 1986) at T  1000-1250 K. As an anion-deficient fluorite, the oxygen ion and its vacancy migration kinetics in YSZ crystal, however, cannot be described solely by a simple vacancy assisted diffusion model (Hull, 2004;Krishnamurthy et al, 2004 (Fig. 8) (Casselton, 1970;Hull, 2004;Krishnamurthy et al, 2004). Interestingly, this trend in ionic conductivity/diffusivity is also commonly observed in a wide range of oxide materials having the same fluorite structure.…”

Optimization of ionic conductivity in doped ceria

“…For increasing doping concentrations, vacancies, on average, will experience more trivalent dopants in their immediate neighborhood. As a result, the number of low barrier migration paths decreases, which at sufficiently high doping concentrations must limit the ionic conductivity (20).…”

Molecular dynamics simulation of zirconia melting

“…Earlier studies [1][2][3][4][5][6][7] make use of either empirical potential functions such as the Lewis-Catlow (LC) potential [9], or ab initio methods such as density functional theory (DFT) to model the interactions in zirconia. While the empirical potential approach is computationally efficient, a feature which is required in order to study diffusion processes involving a time scale of nanoseconds, its accuracy is compromised.…”

“…Structural relaxation, molecular dynamics and kinetic Monte Carlo techniques have been used in studies of zirconia [1,2] and YSZ [3][4][5][6][7], usually focused on oxygen diffusion. For an extensive review see Kilo et al [8].…”