Combustion synthesis and characterization of Cu-Sm co-doped CeO₂ electrolytes

Nano-sized CSO (Ce_0.80Sm_0.20O_2-δ) and CSCO (Ce_0.79Sm_0.20Cu_0.01 O_2-δ) were synthesized by the PVA assisted combustion method, and then characterized by the structure of PVA-cation complexes and nano-powders, as well as mechanical and electrical performance after sintering. The results indicate that the PVA-cation complexes (PVA-(Ce³⁺,Sm³⁺) and PVA-(Ce³⁺,Sm³⁺,Cu²⁺)) were formed by coordinating metal cations to hydroxyl groups, as well as the COO^-1 group derived from the oxidation of PVA with NO₃^-1. Low temperatures (around 200°C) caused intense combustion reactions, resulting in the direct crystallization of cubic fluorite nano-CSO (10-20nm) and nano-CSCO (10-15nm) crystals with homogeneous element distribution. This slight compositional modification of CSO by co-doping with 1mol% CuO resulted in a significantly lowered densification temperature, as well as enhanced mechanical and electrical property. The strength improvement can be ascribed to the dense and fine-grained microstructure without normal grain coarsening, resulting in a transgranular-dominant fracture mode during strength testing.