Hydrothermal synthesis of ultrafine A5Nb4O15 (A=Ba, Sr) powders

A(5)Nb(4)O(15) (A= Ba, Sr) powders with hexagonal perovskite structures have been firstly synthesized by a two-step hydrothermal process. These oxides were crystallized directly from niobium oxide in the presence of potassium basic solutions at 240 degrees C for 48 h. The products were characterized by powder X-ray diffraction and scanning electron microscopy. It was found that the pretreatment of the niobium oxide through the hydrothermal technique firstly was the critical factor to prepare these niobates. Moreover, the alkaline concentration also played an important role in the formation of these niobates. On basis of the experimental data. a possible reaction process for the formation of A(5)Nb(4)O(15) (A= Ba, Sr) was proposed. (C) 2009 Elsevier B.V. All rights reserved.