Influence of cation interdiffusion on electrical properties of doped ceria/lanthanum silicate composite

Abstract La-doped ceria (LDC)/lanthanum silicate (LS) and Ga-doped ceria (GDC)/LS composites were prepared, and the influence of cation interdiffusion during co-firing on the electrical properties of composites was investigated. The electrical conductivity of GDC/LS was lower than that of LDC/LS despite the higher conductivity of GDC compared to LDC. The crystal phases of LDC/LS and GDC/LS were detected as fluorite-type cubic ceria (Fm 3 ¯ m) and a hexagonal lanthanum silicate (P63/m), respectively, by X-ray diffraction (XRD). From energy dispersive X-ray spectroscopy (EDS) measurements, it was found that the compositions of the ceria and silicate phases in LDC/LS were nearly stoichiometric after co-firing. In contrast, interdiffusion between Gd3+ in the ceria phase and La3+ in the silicate phase was recognized for the GDC/LS. The compositions of the ceria and silicate phases in GDC/LS after co-firing were estimated as Gd0.035La0.065Ce0.9O1.95 and La7.910Gd0.423(SiO4)6O0.5, respectively. The Gd3+ substitution for La3+ in the silicate phase in GDC/LS decreased the amounts of 4f site cations. Then, the lattice parameter of the silicate phase decreased. As a result, the decrease in electrical conductivity of GDC/LS is attributed to the decrease in the oxide anion at the 2a site, which is a conduction carrier. It was found from Raman spectroscopy that cation interdiffusion decreased the symmetry mode of the SiO4 tetrahedra for the silicate phase in GDC/LS and brought about increases in the activation energy of electrical conductivity for GDC/LS.