Field-assisted sintering of refractory oxygen-ion and proton conducting ceramics

Solid oxides with high oxygen-ion and proton conductivity have been extensively studied for applications in electrochemical devices such as fuel cells, electrolyzers, sensors, hydrogen separators, etc. However, the preparation of high-density ceramic electrolytes is often complicated by the exceptional refractoriness of most oxygen-ion conducting solid oxide phases. Therefore, conventional sintering of these materials is very energy consuming and low effective. In recent years, non-conventional field-assisted sintering technologies (FASTs) such as spark plasma sintering, flash sintering and microwave sintering, have been developed and applied for sintering dense ceramic electrolytes at reduced temperatures. In this article, the applications of FASTs for densification of refractory oxygen-ion and proton conducting ceramics are reviewed, while the mechanisms, advantages and limitations of these technologies are discussed, with special emphasis on the effects of FASTs on the microstructural and transport properties of sintered materials, and the performance of FAST-processed electrochemical cells.