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 mum) 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).