On the Possibility of Preparing Fine-Particle Barium Zirconate by Hydrothermal Synthesis

The possibility of preparing fine-particle BaZrO3 by hydrothermal synthesis was examined. The samples prepared using three different starting mixtures were characterized by x-ray diffraction, thermogravimetry, and scanning and transmission electron microscopy techniques. By dissolving solid Ba(NO3)2 in a 0.25 M ZrO(NO3)2 solution (pH 1.5), nanocrystalline powder of the stable polymorph M-ZrO2 was obtained (particle size d = 8–10 nm), independent of the Ba(NO3)2 : ZrO(NO3)2 ratio. Hydrothermal treatment of a ZrO(OH)2 gel in neutral (pH 7.0) and ammonia (pH 11.0) media in the presence of Ba(NO3)2 yielded only the metastable phase T-ZrO2 (d = 10–12 nm), whereas treatment under similar conditions with no Ba(NO3)2 in solution resulted in a mixture of M- and T-ZrO2 . The formation of microcrystalline BaZrO3 (d = 2–5 μm) from a ZrO(OH)2 gel was observed only in a high-pH Ba(OH)2 solution (pH 13.0). Attempts to obtain BaZrO3 by boiling an amorphous ZrO(OH)2 gel at 378 K at atmospheric pressure in a high-pH Ba(OH)2 solution (pH 13.0) for 45 min with the use of microwave heating were unsuccessful: the solid phase consisted of x-ray amorphous ZrO(OH)2 .