Preparation and properties evaluation of zirconia-based/Al2O3 composites as electrolytes for solid oxide fuel cell systems

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Yttria-doped zirconia powders containing 3 to 8 mol% Y 2 O 3 and 0 to 20 wt% Al 2 O 3 were prepared by both mixing commercial oxides and a coprecipitation method, and the mechanical and electrical properties have been examined as a function of the Al 2 O 3 content. The bending strength of the composite at room temperature increased with increasing Al 2 O 3 content. In the temperature range 500-1000°C the bending strength increased with Al 2 O 3 content up to 10 wt% and then decreased, the measured value at 1000°C (200 MPa) being higher than those at lower temperatures for cubic zirconia materials. Fracture toughness (K IC ) decreased with increasing Y 2 O 3 content in the Al 2 O 3 -free zirconia materials. Al 2 O 3 additions enhanced the fracture toughness and this was maximum (7 MPa m 1/2 ) for the composite ZrO 2 -3 mol% Y 2 O 3 /10 wt% Al 2 O 3 . The electrical conductivity of cubic ZrO 2 /Al 2 O 3 composites decreased monotonically with Al 2 O 3 content, but in tetragonal ZrO 2 /Al 2 O 3 composites hardly varied or apparently increased up to 10 wt% Al 2 O 3 . At 1000°C the highest electrical conductivity was 0.30 S cm -1 for ZrO 2 -8 mol% Y 2 O 3 , and this decreased up to 0.10 S cm -1 for the composite ZrO 2 -8 mol% Y 2 O 3 /20 wt% Al 2 O 3