Controlled synthesis of Bi₂O₃–YSZ composite powders and their sintering behavior for high‐performance electrolytes

Abstract

Bismuth oxide (Bi 2 O 3 ) is a promising additive to decrease the sintering temperature of yttria-stabilized zirconia (YSZ)-based electrolyte for solid oxide fuel cell application. However, Bi 2 O 3 tends to grow into large column bars (>50 µm) in a chemical coprecipitation method, which dramatically limits the mixing uniformity of Bi 2 O 3 and YSZ, even much worse than that of mechanical mixing. In this study, the reaction temperature was increased from room temperature to 90 • C to increase the number of nucleation during the violate reaction between Bi 3+ solution and YSZ suspension in NaOH. On this basis, the violence of the reaction was further moderated by adding half of NaOH first, then YSZ powders and the other half of an NaOH solution. The size of Bi 2 O 3 was further decreased to sub-micrometer and Bi 2 O 3 was homogeneously mixed with YSZ particles, even when its addition amount was as large as 20 mol%. These composite powders effectively promoted the sintering behavior of YSZ. The sintering temperature of YSZ was decreased to 900 and 1000 • C with 10 and 5 mol% Bi 2 O 3 doping, respectively. Increasing the doping ratio induced severe volatilization of Bi 2 O 3 and pore formation. Raising the sintering temperature (no more than 1200 • C) enhanced the doping effect of Bi 2 O 3 into the YSZ lattice but induced instability in the YSZ crystal structure.

A Comprehensive Understanding of Thermal Barrier Coatings (TBCs): Applications, Materials, Coating Design and Failure Mechanisms

“…Additionally, doping with Bi 2 O 3 and CuO can have favorable effects on sintering, but with limitations induced by the destabilization of the crystalline structure of YSZ [117,118].…”

Perspective Chapter: The Application of Yttria-Stabilized Zirconia (YSZ)

“…A study had been conducted by using 8 mol% Lu 2 O 3 doped 8YSZ and successfully improved the flexural strength of the materials without compromising the ion conductivity [30]. Other studies on the dopant like CuO, TiO 2 and Bi 2 O 3 , also reported the sintering aids for 8YSZ effectively aided the ceramics material to reach full densification at a lower sintering temperature without compromising ion conductivity [31][32][33]. Lower sintering temperature for full densification, which is highly related to the mechanical properties like hardness and fracture toughness, means less energy required during processing.…”

Preparation of Bi2O3–YSZ and YSB–YSZ Composite Powders by a Microemulsion Method and Their Performance as Electrolytes in a Solid Oxide Fuel Cell

“…In addition, the melting point of Bi 2 O 3 , which is commonly used as a liquid-phase-assisted sintering additive for YSZ to enhance its overall performance, is around 825 °C [ 19 , 20 ]. By mechanically mixing Bi 2 O 3 with YSZ or synthesizing Bi 2 O 3 -doped YSZ composite powders, our group and other researchers have demonstrated its effectiveness in lowering the sintering temperature of YSZ electrolytes [ 21 , 22 , 23 ].…”