Cold sintering of BaZr0.8Y0.2O3-δ ceramics: Phase formation and grain boundary properties

Electrochemical devices based on the proton conducting ceramic BaZrO3 have shown their immense potential for efficient energy conversion and gas separation processes at intermediate temperatures. A major drawback of this material class is the inevitably high sintering temperature, which is necessary to reach sufficient densities for gas tightness. Recently, cold sintering has been applied to densify BaZrO3 - BaCeO3 solid solutions at low temperatures using a partial dissolution of the Ce-rich phase. Here, we apply the method to BaZr0.8Y0.2O3-delta (BZY20), which is a Ce-free proton conducting ceramic. We show that densification by cold sintering is viable at temperatures between 150 degrees C and 250 degrees C under uniaxial pressures of 400 MPa and deionized water as a sintering aid. The dissolution of yttrium from BZY20 during cold sintering acts as the trigger for densification at low temperatures but forms Y(OH)(3) as an instable side product. Therefore, we developed a two-step cold sintering process that adds an additional thermal treatment between 900 and 1100 degrees C directly after the cold sintering process to enable electrochemical characterization and transmission electron microscopy investigations.