Site definition and characterization of La-substituted Bi4Ti3O12 thin films prepared by metalorganic chemical vapor deposition

The effects of La content on crystal structure and ferroelectric property of La-substituted Bi4−xLaxTi3O12 were investigated. We utilized as-deposited thin films prepared on (111)Pt/SiO2/Si substrates at 680 °C by metalorganic chemical vapor deposition. The films showed (117) preferred orientation, and the lattice spacing of the (117) plane increased with increasing La content. With the aid of Raman spectroscopy, we found a pronounced site selectivity of La ions for the Bi site (A site) in the pseudoperovskite layer. Even for a small content (x=0.2), an incorporation of La ion into the pseudoperovskite layer greatly enhanced both remanent polarization and coercive field, but improved properties were almost irrespective of La content for x>0.2. For (Bi3.27La0.73)Ti3O12 thin film, we confirmed a good fatigue endurance up to 2×1010 switching cycles.