Study of the Structure, Microstructure, and Electrical Properties of Defect-Induced Ce-Doped SrTiO3 as Solid Electrolyte in IT-SOFC Application

Abstract

Ionic conductors with the composition SrTi_1−xCe_xO₃ (x = 0, 0.02, and 0.04) were synthesized by a high-temperature conventional ceramic route, and their electrical properties were analyzed for use as solid electrolytes in intermediate-temperature solid oxide fuel cells (IT-SOFCs). Scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM-EDX) was used to analyze the compositional homogeneity and morphology of the samples. The phase analysis was performed using X-ray diffraction (XRD), followed by Rietveld refinement, confirming the cubic crystal structure under the space group \(Pm\overline{3 }m\). The bands at 462 cm⁻¹ and 449 cm⁻¹ in the Raman spectrum confirmed the incorporation of Ce at the Ti-site of SrTiO₃. The presence of a negative charge was found from zeta potential analysis, supporting the presence of Ce³⁺ at the Ce⁴⁺site, denoted by \(C{e}_{C{e}^{4+}}^{3+}{^\prime}\), and Ti³⁺ at the Ti⁴⁺ site, denoted by \(T{i}_{T{i}^{4+}}^{3+}{^\prime}\), in X-ray photoelectron spectroscopy (XPS) analysis. The total conductivity of samples showed thermal-dependent Arrhenius behavior with two different activation energy values. The activation energy \(\ge 1 \text{eV}\) in high-temperature regions indicated the migration of doubly ionized oxygen vacancy and \(\le 0.50 \text{eV}\) reflecting the migration of electrons between the degenerate sites of Ti⁴⁺/Ce⁴⁺. The impedance spectroscopy studies suggested the presence of bulk contribution in the electrical properties, and similar charge carriers were responsible for both processes. The impact of oxygen vacancy on electrical conduction was also supported by the magnetic properties, which displayed diamagnetic to paramagnetic phase transition with Ce doping. The highest value of total conductivity was obtained around 0.003 S cm⁻¹ at 610°C, making it a potential candidate for solid electrolytes in IT-SOFC applications.