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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. [ABSTRACT FROM AUTHOR]

Hafnia doping is expected to improve the performance of the silicon‐bond layer of environmental barrier coatings (EBCs) for SiC‐based ceramic matrix composites. The optimal doping ratio, distribution of HfO2, and oxidation mechanism of the bond layer have not yet been fully addressed. A prototype Si–HfO2 bond layer with a designed HfO2‐rich area was used to examine its oxidation behavior. A random dispersion model was developed to calculate the optimal HfO2 doping ratio and its appropriate distribution state. The simulation results recommended that 20–30 vol% is the optimal doping ratio, where HfO2 is well dispersed inside Si without forming networks. This enables HfO2 to react with and consume SiO2 without accelerating oxygen diffusion inside the bond layer. This was confirmed by oxidation experiments on Si–xHfO2 tablets, in which the thinnest thermally grown oxide was achieved for the 20 vol% HfO2‐doped Si tablet. Both the microstructure design and material composition selection are highly important to further boost the performance of the EBCs. [ABSTRACT FROM AUTHOR]