PATHWAYS FOR THE LOW-TEMPERATURE SYNTHESIS OF NANO-SIZED CRYSTALLINE BARIUM ZIRCONATE

The low temperature (below 100 degrees C) sol-precipitation synthesis of nano-sized and crystalline barium zirconate (BaZrO3) powders is discussed. Structural evolution of crystalline BaZrO3 phase was studied under sol-precipitation and hydrothermal conditions. Chemical analysis showed that the zirconium precursor precipitated during the early stages of the reaction (t<5 min) led to nano-sized (10-100 nm) hydrous oxide primary particles. The alkaline earth cation, occluded in the entrained liquid, subsequently intercalated into the primary particles to transform originally amorphous transition metal-rich precipitates into crystalline BaZrO3 at temperatures as low as 90 degrees C. The precipitate crystal phase development exhibited a significant dependence on time (t=5-240 min) and temperature (90-205 degrees C). Increasing time or temperature enhanced the formation of the perovskite phase. BaZrO3 synthesis was also characterized by another salient feature in that primary particles grew into fairly uniform (1-3 mu m) pseudospherical secondary particles by what appeared to be a particle aggregation mechanism. This is one of the few systems that exhibit two simultaneous processes: (1) crystallization of primary particles with a chemical change and (2) formation of uniform, spherical secondary particles via particle aggregation.