Low temperature synthesis of lithium niobate powders based on water-soluble niobium malato complexes

Pure lithium niobate (LN) powders were prepared by a wet-chemical method. Hydrated niobium oxide was dissolved in a hot aqueous solution of oxalic acid, followed by the precipitation of niobic acid by the addition of ammonia solution until pH=11. Niobic acid precipitated was dissolved in an aqueous solution of dl-malic acid. A small amount of the Nb–malic complex synthesized was isolated and characterized by thermogravimetry (TG) and infrared (IR) spectroscopy, and the molecular composition of the complex was determined as H[Nb2O(H3C4O5)3]. The exact content of niobium in the stable solution of Nb–malic solution was determined by gravimetric analysis. Stoichiometric amount of lithium carbonate was added into Nb–malic solution. After the solvent elimination, the remaining solid powder was calcined at 350 °C, ground and calcined over a temperature range from 300 to 900 °C. Calcined powders were characterized by X-ray diffraction (XRD) and Raman spectroscopy. Crystalline LN phase was identified at 500 °C/2 h, although the total elimination of the inorganic carbon occurred only at 650 °C/2 h.