Correlation between structure, microstructure, and ferroelectric properties of PbZr0.2Ti0.8O3 integrated film:: Influence of the sol-gel process and the substrate

The properties of a ferroelectric material deposed as a thin film on a substrate depend on the method of preparation and on the nature of the substrate used. The present work reports fine characterization by x-ray diffraction of structural modifications (cell parameters, preferential orientations) and microstructural modifications (ferroelectric domain arrangement) and electric measurements of a ferroelectric film as a function of its method of preparation (sol-gel process, pyrolysis, annealing) and the nature of its substrate (crystalline structure, crystallographic orientation, thermal coefficient of dilation). Due to the elaboration process, lead zirconate titanate (PZT) films have grain size smaller than 0.3 mu m and consequently modified cell parameters a parameter (higher a parameter, smaller c parameter, and consequently smaller c/a tetragonality). Thermal treatment induces specific stresses between the PZT film and the substrate that modify the ferroelectric domain microstructure of the PZT grains: the microstructure is a-domain-type on SiO2 and Si, normal on Al2O3 and c-domain-type on SrTiO3 and MgO. Epitaxial orientation of the PZT grains is observed on bare SrTiO3 and MgO single crystals due to their oxide nature, cubic structure with cell parameters close to those of the PZT. On the other hand, the expected (111) orientation of PZT grains is not observed on (111) fiber axis Pt electrode, although cubic cell parameters of Pt are close to those of the PZT. The elaboration process (deposit of 0.2 mu m in one coating) and the poor chemical affinity between mm platinum and PZT could be an explanation of the random orientation of the PZT grains. Structural and microstructural characteristics of the PZT grains do not affect drastically the electrical properties of the PZT film. By comparison, the presence of porosity and a pyrochlore phase has disastrous consequences. An improvement of the electrical properties is observed for dense PZT film with (100) oriented grains whose domain microstructure is c-domain-type. (C) 1998 American Institute of Physics. [S0021-8979(98)05018-X]