Effect of oxygen nonstoichiometry on electrical conductivity and oxygen transport parameters of Cu-substituted La_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ perovskite oxides

A parametric evaluation on a series of oxygen-deficient Co-rich La_0.5Sr_0.5Co_0.8Fe_0.2−xCu_xO_3−δ perovskite oxides (x = 0–0.20) is reported, for potential utility towards oxygen separation membrane and fuel cell application. Oxygen transport property is influenced by several parameters, including oxygen vacancy concentration, crystal structure, microstructure, electrical conductivity, and conductivity relaxation. X-ray photoelectron spectroscopy study revealed that oxygen nonstoichiometry in the prepared oxides increases with Cu-substitution level. The structural study confirmed that this material family has a cubic structure with Pm 3- m space group with lattice size decreasing with increase in x. The microstructure of studied oxides showed that the average grain size of the sample considerably decreases with Cu-substitution. Iron substitution with copper remarkably enhances the electrical conductivity, which can be explained with defect chemistry. The bulk diffusion coefficient (D_chem) and surface exchange coefficient (K_chem) of La_0.5Sr_0.5Co_0.8Fe_0.2−xCu_xO_3−δ oxides were obtained using an electrical conductivity relaxation technique, and La_0.5Sr_0.5Co_0.8Cu_0.2O_3−δ oxide was found to have higher D_chem (1.1 × 10⁻⁴ cm² s⁻¹) and K_chem (8.5 × 10⁻⁵ cm s⁻⁵) among them. This work demonstrates that the proposed Co-rich La_0.5Sr_0.5Co_0.8Fe_0.2−xCu_xO_3−δ perovskite with Cu-substitution level x = 0.20 can be considered a promising material for enhanced oxygen transport.