Ferroelectricity of lanthanum-modified lead titanate thin films obtained by a diol-based sol-gel method

Lanthanum-modified lead titanate thin films have been prepared by a diol-ba sed sol-gel method from precursor solutions with a growing excess of PbO. T he films were crystallized with thermal treatments at 650 degrees C and hea ting rates of 10 degrees C min(-1) and higher than 500 degrees C min(-1) by direct insertion in a pre-heated furnace. The structure, microstructure, a nd composition of the films were studied by grazing-incidence X-ray diffrac tion, electron microscopies, and energy-dispersive X-ray spectroscopy. A 20 mole % excess of PbO must be included in the precursor solution in order t o compensate PbO volatilization occurring during the thermal treatment and, thus, obtain single-phase perovskite-type structure films. Non-textured po rous films were obtained when a 10 degrees C min(-1) rate is used, whereas [001]/[100] oriented films without porosity were obtained when rapid heatin g was used. Dielectric permittivity, ac current density, hysteresis loops, and switching curves were measured in the films. Values of remanent polariz ation and coercive field are comparable to those reported for similar films . The effects on the ferroelectric properties of an electrical and a post-c rystallization thermal treatments were characterised.