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 th e substrate used. The present work reports fine characterization by x- ray diffraction of structural modifications (cell parameters, preferen tial orientations) and microstructural modifications (ferroelectric do main 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, cry stallographic orientation, thermal coefficient of dilation). Due to th e 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 stresse s between the PZT film and the substrate that modify the ferroelectric domain microstructure of the PZT grains: the microstructure is a-doma in-type on SiO2 and Si, normal on Al2O3 and c-domain-type on SrTiO3 an d MgO. Epitaxial orientation of the PZT grains is observed on bare SrT iO3 and MgO single crystals due to their oxide nature, cubic structure with cell parameters close to those of the PZT. On the other hand, th e expected (111) orientation of PZT grains is not observed on (111) fi ber 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 o ne 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 no t affect drastically the electrical properties of the PZT film. By com parison, the presence of porosity and a pyrochlore phase has disastrou s consequences. An improvement of the electrical properties is observe d for dense PZT film with (100) oriented grains whose domain microstru cture is c-domain-type. (C) 1998 American Institute of Physics. [S0021 -8979(98)05018-X]