Unraveling Crystal Structure and Transport Properties of Fast Ion Conducting SrCo_0.9Nb_0.1O_3−δ

Abstract

SrCo0.9Nb0.1O3−δ (SCN) has been investigated for oxygen transport membrane and solid oxide fuel cell applications as it is more stable than the state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) material. Here, the crystal structure and transport properties of SCN were systematically investigated. Combined neutron and high-temperature X-ray powder diffraction analyses over the temperature range of 25–800 °C showed that the crystal structure of SCN belongs to the tetragonal space group P4/mmm with the unit cell ac × ac × 2ac, where ac is the lattice parameter of the cubic perovskite at temperatures <160 °C. The tetragonal (P4/mmm) to cubic (Pm3̅m) phase transition occurred in SCN with increasing temperature. This phase transition affected the electrical conductivity, whereas the impact on the magnetic susceptibility was not significant. The surface exchange and diffusion coefficients of SCN in the temperature range of 600–850 °C were characterized by electrical conductivity relaxation and oxygen permeation measurements. The self-diffusion and surface exchange coefficient of SCN are comparable with those of BSCF. Hence, SCN shows promise as a next-generation mixed ionic–electronic conducting ceramic.