Combined effect of grain size and tensile stresses on the ferroelectric properties of sol-gel (Pb,La)TiO3 thin films

Transmission electron microscopy has shown that the grain size of sol-gel-prepared lanthanum-modified lead titanate films increases from similar to 100 to similar to 1 mu m when the excess of PbO in the precursor solution is reduced from 20 to 10 mol%, Switchable polarization is higher in the films with a smaller grain size. Profilometry and the temperature dependence of the dielectric permittivity indicate that films are tensile stressed by the substrate. The grain-size effect on polarization switching is explained by taking into account this tensile stress, which is thought to induce some a-domain orientation and 90 degrees domain wall clamping in the grains attached to the substrate.