Investigations on sol-gel derived lanthanum doped lead titanate (PLT) films

Pb1.05-xLax(Ti1-x/4)O-3 (x = 0.00, 0.05, 0.1, 0.15, 0.20, 0.25 and 0.30) thin films were deposited on sapphire (0001) substrates by an acetic acid modified sol-gel technique. The films were characterized, using various techniques, in terms of their phase formation behavior, composition, microstructure and electrical characteristics. It was observed that the sol-gel derived films crystallize into the perovskite phase without any paraelectric cubic pyrochlore phase formation. For less than 15 at% lanthanum composition, the films show a tetragonal phase which transforms into a cubic phase for higher lanthanum content. The observed reduction of the tetragonal distortion with La addition is due to the pronounced shrinkage of the 'c' axis. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical composition. The XPS results are in excellent agreement with the nominal composition of the films. All films are extremely smooth, crack- and pinhole-free, and have a dense uniform microstructure. The grains are not single crystalline, instead each grain is the aggregate of numerous tiny perovskite crystallites. The apparent grain size increases with La addition. The values of dielectric constant, remnant polarization, saturation polarization and coercive field are comparable with the best reported values of sol-gel derived PLT thin films.