Processing of lithium niobate and potassium lithium niobate films using environmentally-friendly aqueous precursor solutions

Lithium niobate(LiNbO3) and potassium lithium niobate(K(3)Li(2)b(5)O(15)) 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.