Aqueous chemical solution deposition of ferroelectric Ti4+ cosubstituted (Bi,La)(4)Ti3O12 thin films

Abstract

A new, entirely aqueous method for the deposition of ferroelectric lanthanum substituted bismuth titanate including cosubstitution of Till with higher valent metal ions (W6+, Moll, Nb5+, and V5+) is presented. The strong tendency toward hydrolysis and condensation of highly valent metal ions, causing precipitation of (oxy)hydroxides, was adequately prevented by new synthesis routes for stable, aqueous (mono)metal ion precursor solutions based on citratoperoxo or nitrilotriacetatoperoxo complexes. The (mono)metal ion precursors are optimized for convenient mixing into multimetal ion precursors with the desired composition, which are deposited using spin-coating. The effect of the La3+ content as well as the different cosubstitutions on the films' ferroelectric remanent polarization, crystalline, and microstructural properties was studied. A maximal 2P(r) value of 17.2 gamma C/cm(2) was obtained for the Bi3.5La0.5Ti2.97V0.03O12+delta thin film after annealing at a temperature as low as 650 degrees C. The cosubstituting metal ions affect both the crystallographic orientation and the grain growth behavior of the BLTM thin films. A reduction of the c-axis preferential orientation and an enhanced grain growth correlate with improved remanent polarization. The general potential of this original aqueous route is two-fold: synthesis of even highly complex multimetal oxide compositions is accomplished easily at low temperatures and a strong ecologic and economic advantage over solvent-based chemical routes is obtained.