Chemical synthesis of lithium niobate powders (LiNbO3) prepared from water-soluble DL-malic acid complexes

Lithium niobate powders were prepared from LiCl and a new water-soluble complex synthesized with DL-malic acid (MA) and NbCl5, using neither dry solvents nor an inert atmosphere. A stable aqueous solution was prepared containing niobium chloride and MA, with a molar ratio of [MA]:[Nb] = 2:1 at pH = 7. UV-Raman spectroscopy of the Nb-MA aqueous solution indicated the coordination of the Nb with the deprotonated alcohol and with the carboxylic groups of the MA molecule. Continuous heating of a mixed aqueous solution containing MA, ammonia, Li, and Nb ions at 70 degreesC produced a pale yellow powder which was heat treated at 350 degreesC for 5 h to sublimate NH4Cl, eliminating more than 99.5 wt % of the chlorine. The Nb-Li-MA heated-treated powder was calcined under different conditions of temperature and time. The formation of pure LiNbO3, free from amorphous carbon, which occurred at temperatures greater than 650 degreesC, was confirmed by a combined analysis using X-ray diffraction and UV-Raman spectroscopy.