Ionic conductivity and transport mechanism in Sm-doped CeO2 ceramics prepared from ionic gelation-derived oxide powders

Rare-earth-doped ceria is being investigated for applications, such as solid oxide fuel cells (SOFCs), oxygen sensors, thermobarrier coatings, among others. In all these applications, finely dispersed starting powders are essential for preparing ceramics with parameters that meet technological requirements. In the present work, Sm-doped CeO 2 ceramics were prepared by ionic gelation (IG) and subsequent thermal treatment. Ionic solutions of sodium alginate and metal nitrates (Ce(NO 3 ) 3 .H 2 O, Sm(NO 3 ) 3 .H 2 O) were gelled, followed by a thermal treatment at 500°C for 4 h to obtain powders. After, they were pressed into pellets and sintered at 1400°C to form dense ceramics. The as prepared Ce 1-x Sm x O 2-x/2 (x=0.1, 0.2, 0.3, 0.4, 0.5) materials were characterized morphologically and structurally by scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared spectroscopy (IR). XRD analysis confirms samarium incorporation in the CeO 2 lattice, evidenced by diffraction peaks shifts. The ceramics relative density, a key factor for the reliable performance of electrolyte materials was also analyzed. AC impedance analysis was performed to study the ionic conductivity of the obtained ceramics. The impedance data were modeled using equivalent circuits to study the ionic conductivity and the electrolyte materials transport mechanisms. The bulk, grain boundary and total conductivity were analyzed and compared to all compositions. The intrinsic grain boundary conductivity and space-charge layer properties were further studied using a Mott-Schottky approximation to investigate the doping effect. This study demonstrates the potential of ionic gelation for the synthesis of Sm-doped CeO₂ ceramics with controlled structural and electrochemical properties, making them suitable for SOFCs applications.