Formation mechanism of NaNbO_3 powders during hydrothermal synthesis

摘要

Hydrothermal synthesis of NaNbO_3 fine powders was investigated, and the formation mechanism was revealed. The lowest temperature to form NaNbO_3 powders was about 140 ℃. An intermediate hexaniobate, Na_8N-b_6O_(19)·13H_2O, was formed first before the precursors were eventually converted to the perovskite phase. The step of dissolving Nb_2O_5 powders in OH~- solution and forming Nb_6O_(19)~(8-) ion was very important to the synthesis of NaN-bO_3. For [OH~-] = 3.0 M, Nb_2O_5 had the highest yield. There was another dissolvable sodium niobate in the hydrothermal system, which was stable when [OH~-] = 1.2 M. The reaction mechanism was in situ transformation. The reaction speed first increased then decreased with [OH~-]. High [OH~-] is not always favorable in preparing perovskite NaNbO_3, and there is an optimum [OH~-].