Materials design of solid electrolytes.

S olid electrolytes play an important role in several technological applications, such as fuel cells. Optimization of such materials is often done by trial and error. The work of Andersson et al. (1) in this issue of PNAS demonstrates that the choice of dopants can be guided by computer simulations, in which parameters that are essential for the high ionic conductivity are determined from a series of firstprinciples density functional theory (DFT) calculations (2). The material of interest is ceria (CeO2), which can be doped to optimize the ionic conductivity. The parent compound has a simple cubic structure (Fig. 1), in which the Ce ions form a face-centered-cubic (fcc) structure and the oxygen ions form a simple cubic sublattice. The current flows by means of oxygen ions, which are transported through the lattice in a vacancy-assisted activated process. Vacancies occur, for example, when ceria is doped with lower valence cations, but interactions between dopants and vacancies often prevent the vacancies from being mobile. The authors make