Indentation fracture toughness and hardness of solid oxide fuel cell electrolyte material

Yttria-stabilized cubic zirconia is well known the material that possesses high oxygen ionic conductivity and chemical stability over wide ranges of temperature and oxygen partial pressure and thus it is widely used as an oxygen sensor, thermal barrier and solid oxide fuel cell (SOFC) electrolyte. In the present study, 8 mol% yttria-stabilized cubic zirconia with SiO2 addition up to 10 wt% was studied with respect to the microstructure, fracture toughness and hardness. XRD results showed that SiO2 had very limited solubility of 0.3 wt% in cubic zirconia. This suggests that only small part of SiO2 dissolved in cubic zirconia and the rest of SiO2 segregated at grain boundaries and multiple junctions. This glassy phase also wetted the zirconia grains and prevented the grain growth and the formation of facetted grains. Both hardness and fracture toughness were measured using a Vickers indenter. It is observed that the introduction of SiO2 decreased the hardness and increased the fracture toughness of cubic zirconia. The hardness and fracture toughness also showed the same trend with increasing SiO2 content.