The low temperature (below 100 °C) sol-precipitation synthesis of nano-sized and crystalline barium zirconate (BaZrO3) powders is discussed. Structural evolution of crystalline BaZrO 3 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 BaZrO a at temperatures as low as 90 °C. The precipitate crystal phase development exhibited a significant dependence on time (t = 5-240 min) and temperature (90-205 °C). Increasing time or temperature enhanced the formation of the perovskite phase. BaZrO 3 synthesis was also characterized by another salient feature in that primary particles grew into fairly uniform ( 1-3/,tm) 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. 17. P. Phu[k, D. (. Grundy / m A~vnthesis ~?f nanosized cr3,vtalline BaZr~ ),.