A new family of Cu-doped lanthanum silicate apatites as electrolyte materials for SOFCs: Synthesis, structural and electrical properties

Abstract

La9.67Si6-xCuxO26.5-x (LSC, x = 0, 0.1, 0.3 and 0.5) are synthesized by a citric-nitrate method. Substitution Si with Cu promotes the densification process of silicate apatite. Unit cell parameters and volume increase linearly with Cu content. The Rietveld refinement reveals a much more distorted (Si,Cu)O4 tetrahedra in the oxygen stoichiometric La9.67Si5.5Cu0.5O26 sample. The structural observation from high temperature XRD implies a second-order phase transition in La9.67Si5.5Cu0.5O26. Cu-doping decreases the activation energy of oxygen ion conduction and increases the conductivity of LSC materials in the temperature range of 550–800 °C. La9.67Si5.5Cu0.5O26 shows the conductivity values of 29.3 and 12.3 mS cm−1 at 800 °C and 650 °C, respectively. The oxygen ion transference number of La9.67Si5.5Cu0.5O26 is higher than 0.99. These attractive properties make the La9.67Si5.5Cu0.5O26 a promising oxygen ion conducting electrolyte for applications of solid oxide fuel cells, oxygen sensors, oxygen separation membranes, etc.