Coprecipitation method for synthesizing LaNbO4 powders without niobium chloride

A new coprecipitation method including two optional routes-liquid-liquid route and liquid-solid route for synthesizing lanthanum orthoniobate (LaNbO4) powders with La-2(CO3)(3) and Nb2O5, which are economic and locally available, has been developed. The liquid-liquid route is easy and fast to realize, and ultrafine LaNbO4 powders with purity of 99.7% and d(50) < 1 mum have been prepared with this method, while the liquid-solid route has an advantage in the particle size control and can obtain powders more uniform in size. Presence of impurity and its control in the liquid-liquid route has been analyzed in light of polyatomic acid reaction theory. It is proposed that K2LaNb5O15 impurity appear due to the hydrolization of homo-polyatomic acid niobium anion and precipitation of the formed salt. In order to avoid the formation of the impurity, it is critical to prevent the formation of the homo-polyatomic acid niobates, and an alkalinic reaction environment (pH9similar to10) is favorable. For powders already containing the impurity phase, an alkalinic solution treatment can effectively lower the impurity content.