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.