Microstructure-ferroelectric properties relationships in sol-gel prepared lanthanum modified lead titanate thin films

Transmission electron microscopy is used to investigate the effect of the e xcess of PbO and the temperature of crystallization on the grain size of so l-gel lanthanum modified lead titanate thin films. Grain size is found to i ncrease from similar to 100 nm to similar to 1 mu m when the excess of PbO in the precursor solution is reduced from 20 to 10 mol%, but it is not sign ificantly affected by raising the temperature from 650 to 700 degrees C. Fi lms ferroelectric characterization shows that the switchable polarization i s higher in the films with a smaller grain size. This effect is explained b y taking into account the presence of a tensile stress at the film-substrat e interface, which clamps 90 degrees domain walls. This stress is higher in coarse grained films, most of whose grains are in contact with the substra te, than in the fine grained films. Therefore, 90 degrees domain wall movem ent is easier in fine grained films. (C) 1999 Elsevier Science Limited. All rights reserved.