Processing of Lithium Niobate and Potassium Lithium Niobate Films Using Environmentally-Friendly Aqueous Precursor Solutions

Abstract

Lithium niobate(LiNbO₃) and potassium lithium niobate(K₃Li₂Nb₅O₁₅) films can be prepared using environmentally-friendly aqueous precursor solutions. The process is reviewed by focusing on chemical properties and structure of a water soluble Li-Nb precursor molecule. The Li-Nb precursor molecule appears to be an oligomer having -O-Nb-O-Li-O- bonds with [NbO₃(OH)₃]^4- octahedral structure. The water solubility of the oligomer molecule may be due to the hydroxy groups surrounding the molecule, which makes the solution alkaline. This alkaline solution can be neutralized by acetic acid. High quality LiNbO₃ and K₃Li₂Nb₅O₁₅ films crystallize by heat-treatment at low temperatures. The low crystallization temperature of the LiNbO₃ film can be achieved because the precursor film contains no carbon residues, and the precursor molecule is designed to have the skeletal structure in the LiNbO₃ crystal. Micro-patterning of LiNbO₃ films are conducted by means of a coating process using neutralized aqueous precursor solution in the photolithographic technique. Aqueous precursor solutions with controlled composition can lead to the development of the processing of high quality powders and films in lead-free piezoelectric (K, Na, Li)NbO₃ ceramics and LiNbO₃ waveguides.