Microhardness and fracture toughness of Ce_0.9Gd_0.1O_1.95 for manufacturing solid oxide electrolytes

Synthesis of nanocrystalline gadolinium doped ceria (Ce_0.9Gd_0.1O_1.95) was attempted by nitrate-fuel combustion technique involving different organic fuels namely urea, citric acid, glycine and poly ethylene glycol. As-combusted ceria precursors were calcined at 700 °C for 2 h for obtaining fully dense, nanocrystalline ceria powders. Cylindrical ceria discs were fabricated by uni-axial pressing and sintered intentionally at low temperature of 1200 °C for 2 h for assessing the sintering characteristics of the nano powders as well as the mechanical performance of the sintered ceria body. The study confirms that the nano powders could be sintered to 98% theoretical sintered density at 1200 °C with a grain size of 400 nm to 1 μm. The sintered samples exhibited the Vickers microhardness of 8.82 ± 0.2 GPa and the fracture toughness of 1.75 ± 0.3 MPa m^1/2 at a load 20 N for glycine and citric acid fuels derived ceria, respectively. A comparison between the fuels was made with respect to the sintering and mechanical properties of doped ceria. Citric acid and glycine fuels resulted in sintered ceria with high hardness where as the urea and polyethylene fuels derived nano ceria resulted in high fracture toughness.