Comparison of Aqueous and Non-aqueous Soft-Chemical Syntheses of Lithium Niobate and Lithium Tantalate Powders

Lithium niobates and tantalates have a number of characteristics exploitable for optical and electrical devices that include ion conductivity, self-activating or dopant luminescence, piezoelectricity, pyroelectricity and ferroelectricity. To form these materials as nanometric powders or thin-film coatings, soft-chemical processing is required, and a limited number of procedures have been reported. We have explored two soft-chemical routes to lithium niobate and lithium tantalate materials: a non-aqueous procedure and an aqueous procedure. The non-aqueous procedure, which utilizes 1,4-butanediol and simple chemical precursors produces pure phase rhombohedral LiTaO(3) and LiNbO(3). For aqueous synthesis, we utilize the single-source polyoxoniobate salt: Li(8)[M(6)O(19)]center dot xH(2)O (M = Nb, Ta) in a hydrothermal reaction. If LiOH is added, the product is rock-salt type Li(3)MO(4)- Without LiOH, other phases are observed. The products are characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, compositional analysis, and thermogravimetry, and the two soft-chemical processes are compared.