Mechanical and electrical properties of Sc2O3-doped zirconia ceramics improved by postsintering with HIP

The microstructure, fracture strength, and electric conductivity of 3–7 mol% Sc2O3-doped zirconia polycrystals fabricated by sintering at 1300°C for 1 h in air, followed by hot isostatic pressing (HIP) at 196 MPa at 1300 and 1450°C for 1.5 h in an Ar gas atmosphere, have been investigated. Significant improvements in the fracture strength and also enhancement in the electric conductivity were obtained by the HIP treatment. We obtained HIPed zirconia polycrystals doped with 3.5 mol% Sc2O3 having an average fracture strength as high as 1770 MPa, high fracture toughness as 5.6 MPa m1/2, and an electric conductivity of 0.08 S cm−1 at 1000°C. The present zirconia ceramics which had uniform submicron grains of tetragonal phases and were stabilized with 5 and 6 mol% Sc2O3 doping showed excellent mechanical strength (1330, 1140 MPa), good fracture toughness (4.8, 4.1 MPa m1/2), and good conductivity (0.15, 0.18 S cm−1, respectively), both being higher than those reported before. The present HIPed zirconia ceramics are some of the candidate materials for an electrolyte of planar-type solid oxide fuel cells.