Entropic stabilization plays a key role in the non-uniform distribution of oxygen ions and vacancy defects in gadolinium-doped ceria

Abstract

Gadolinium-doped ceria (GDC) is an important fast oxygen ion conductor. O2--ion hopping in different cation environments of GDC is probed using molecular dynamics (MD). We find that at equilibrium, the...

Emergent ionic conduction in aliovalently-doped fast ion conductors

“…Here, the distribution coefficient is given by 21 Δ ε – ε ′ = 〈exp(− β Δ U )〉.Δ U is the energy change associated with moving the vacancy defect from environment ε ′ to ε . The angular bracket implies averaging over an ensemble of configurations analogous to the particle insertion method.…”

“…61–64 Δ ε – ε ′ contains contributions arising from energetic interactions, vibrational entropy and configurational entropy. 21 Therefore, π O–V ( ε ) is an emergent quantity for which no closed form expression is available.…”

“…At the atomistic scale, the oxygen migration depends on the specic details of the local cation arrangement, whereas, the ionic conductivity is an emergent property that is determined by the overall interactions and exchange of ions between different parts of the material system. [17][18][19][20][21][22] So far, a quantitative relationship between microscopic quantities and macroscopic ionic conductivity for moderately to heavily doped oxide materials has been missing. In contrast, in the limit of dilute dopant concentration 23 an expression is available that directly relates charge carrier concentration to conductivity.…”

“…Classical molecular dynamics (MD) simulations have greatly contributed to our understanding of the ion conduction mechanism at the atomistic scale. [19][20][21][24][25][26][27] Oxygen migration in YSZ mainly proceeds via the vacancy-assisted hopping mechanism. 23,28 Here we explore the electric eld driven oxygen hopping behavior in YSZ using MD.…”

“…While solving the equation of motion, the force due to external eld is added to the interactions between the charged ionsthe latter is calculated using a classical interatomic potential. MD studies in the absence 20,21,24,27,29 and presence of an electric eld (∼0.1-30 MV cm −1 ) [30][31][32][33][34][35][36] have been reported. For any ionic material, the application of an electric eld alters the underlying potential energy landscape.…”