Scavenging of Siliceous Grain-Boundary Phase of 8-mol%-Ytterbia-Stabilized Zirconia without Additive

The grain-boundary conductivity (σ_gb) of 8-mol%-ytterbia-stabilized zirconia increased markedly with heat treatment between 1000° and 1300°C with a slow heating rate (0.1°C/ min) before sintering. The extent of the σ_gb improvement was the same or larger than that via Al₂O₃ addition. The heat treatment did not affect the grain-interior conduction when sintered at 1600°C, while Al₂O₃-derived scavenging significantly did, given the larger increment of total conductivity in the heat-treated sample. The formation of a silicon-containing phase in a discrete form was suggested as a possible route of scavenging the resistive phase from the correlation between average grain size and σ_gb.