New insights into the dopant size-ionic transport relationship for Ln2O3-doped Ceria (Ln = Yb, Er, Ho, Y, Dy, Gd, Eu, Sm, Nd, and La) electrolytes through statistical moment calculations

Abstract

The type of dopant used is one of the crucial factors for the improvement of rare-earth-doped ceria (CeO${}_2$) electrolytes in solid oxide fuel cell technologies. Nonetheless, the mechanism leading to the relationship between dopant size and electrical properties remains incomplete. Utilizing statistical moment method (SMM), we investigate the elastic strain caused by the size misfit between the dopants and host cation and its influences on the ionic transport in Ln${}_2$O${}_3$-doped CeO${}_2$ (Ln = Yb, Er, Ho, Y, Dy, Gd, Eu, Sm, Nd, and La). The lattice distortion at the initial point controls the preferential location of oxygen vacancy around dopant and that at the transition point governs the open channels for vacancy migration. The effective binding energy between oxygen vacancy and dopant depends non-linearly on the dopant radius while the vacancy migration increases as the dopant radius becomes larger. The behavior of effective binding energy is ascribed to the competitive effect between the elastic and Coulomb energies. The weakest dependence of ionic conductivity on the temperature is found for Ln = Sm while the strongest influence is exhibited for Ln = Yb. The curves of activation energy and ionic conductivity versus the dopant radius reveal the optimal dopant for Ln${}_2$O${}_3$-doped CeO${}_2$ electrolytes. The dopant size becomes an essential factor in controlling the ionic conductivity of ceria-based solid electrolytes. Our results are well supported by other calculations and experiments. This work thereby offers the new insights into the fundamental atomistic mechanisms that control the dopant size-ionic transport relationship in rare-earth-doped CeO${}_2$ electrolytes.