The effect of the addition of a small amount of CuO on the microstructure, hardness, fracture toughness and electrical conductivity properties of 8YSZ were investigated using 8 mol% yttria-stabilized cubic zirco-nia (8YSZ). The addition of 1 wt% CuO to 8YSZ powders were doped using a colloidal process. Undoped and CuO doped 8YSZ specimens were pressureless sintered at 1400 °C for 10 h. The grain size measurement results showed that the presence of CuO as a intergranular second phase at the grain boundaries of the 8YSZ gave rise to a decrease in the grain size. The fracture toughness values for undoped and 1 wt% CuO-doped 8YSZ specimens were obtained as 1.79 and 2.20 MPa.m~(1./2), respectively. The decrease in the grain size of the 8YSZ with CuO addition caused an increase in the fracture toughness. The electrical conductivity of the undoped and 1 wt°/o CuO-doped 8YSZ specimens was measured using a frequency response analyzer in the frequency range of 100 mHz-13 MHz and at the temperature range of 300-800 °C. The electrical conductivity results showed that there was a decrease in the grain interior, and specific grain boundary conductivity, with the addition of a small amount of CuO to 8YSZ. The presence of a second phase layer with high resistance at the grain boundaries of the 8YSZ caused a decrease in the specific grain boundary conductivity.
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