Higher conductivity Sm 3+ and Nd 3+ co-doped ceria-based electrolyte materials

Abstract

A co-doping strategy is used to enhance the ionic conductivity of doped ceria. Recent density functional theory has suggested that Pm with atomic number 61, is the ideal dopant exhibiting low activation energy for oxygen diffusion, and consequently high ionic conductivity. Taking the atomic number of Pm 3+ into account, Sm 3+ and Nd 3+ are selected as co-dopants for ceria to test this hypothesis. Different compositions of Sm x / 2 Nd x / 2 Ce 1 − x O 2 − δ ( x = 0.01–0.20) are synthesized using conventional solid state route. The lattice parameters are estimated after the detailed analysis of X-ray diffraction data using least-squares extrapolation technique. The lattice parameter in Sm x / 2 Nd x / 2 Ce 1 − x O 2 − δ system obeys Vegard's law, even at higher dopant concentration, indicating that short-range oxygen vacancy ordering is comparatively lower than in other systems. The ionic conductivity of the samples is measured in the temperature range of 250 °C to 700 °C, using two-probe electrochemical impedance spectroscopy technique. The grain contribution to the ionic conductivity for Sm x / 2 Nd x / 2 Ce 1 − x O 2 − δ is disc ussed in detail. The grain ionic conductivity of Sm 0.075Nd 0.075Ce 0.85O 2 − δ is found to be 30% higher than that of Gd 0.10Ce 0.90O 2 − δ at 550 °C. It is shown that Sm x / 2 Nd x / 2 Ce 1 − x O 2 − δ is an electrolyte that obeys the Meyer–Neldel rule. In the high temperature (> 475 °C) region, the activation energy shows a minima at 5mol% dopant concentration with the value of 0.62 eV.