Preparation of Bi₂O₃-YSZ and YSB-YSZ Composite Powders by a Microemulsion Method and Their Performance as...

Bi₂O₃ is a promising sintering additive for YSZ that not only decreases its sintering temperature but also increases its ionic conductivity. However, Bi₂O₃ preferably grows into large-sized rods. Moreover, the addition of Bi₂O₃ induces phase instability of YSZ and the precipitation of monoclinic ZrO₂, which is unfavorable for the electrical property. In order to precisely control the morphology and size of Bi₂O₃, a microemulsion method was introduced. Spherical Bi₂O₃ nanoparticles were obtained from the formation of microemulsion bubbles at the water-oil interface due to the interaction between the two surfactants. Nanosized Bi₂O₃-YSZ composite powders with good mixing uniformity dramatically decreased the sintering temperature of YSZ to 1000 °C. Y₂O₃-stabilized Bi₂O₃ (YSB)-YSZ composite powders were also fabricated, which did not affect the phase of YSZ but decreased its sintering temperature. Meanwhile, the oxygen vacancy concentration further increased to 64.9% of the total oxygen with the addition of 5 mol% YSB. In addition, its ionic conductivity reached 0.027 S·cm^-1 at 800 °C, one order of magnitude higher than that of YSZ. This work provides a new strategy to simultaneously decrease the sintering temperature, stabilize the phase and increase the conductivity of YSZ electrolytes.