Spark plasma sintering of single-phase high entropy A2Zr2O7 pyrochlore oxides and the aqueous durability analysis

Abstract

In this study, a secondary sintering process was adopted to optimize the preparation process of single-phase high entropy A2Zr2O7 pyrochlore-based waste forms by spark plasma sintering (SPS). This method eliminates the significant internal stress when preparing samples directly by SPS, and thus well preserves the integrity of the samples after annealing. The phase composition, microstructure, and leaching properties of high entropy A2Zr2O7 pyrochlore were systematically investigated. Owning to the low sintering temperature (1450 °C) and short held time (3 min), the high entropy A2Zr2O7 pyrochlore exhibited a fine average grain size of 0.8 μm. The high entropy A2Zr2O7 pyrochlore oxides exhibit a reliable leaching resistance with low normalized release rates around 10−5 g/(m2∙d) for all elements. For the high entropy systems, the aqueous durability is mainly determined by the average grain size of ceramics and the temperature of the leaching test as well as traditional pyrochlore ceramics solidification.