| A pneumatic pressure charge technique was developed for the characterization of the longitudinal piezoelectric (d33) coefficient of piezoelectric thin films using the direct piezoelectric effect. It was found that the stress rig applied both normal and in-plane stresses to the film. However, the induced charge due to the in-plane stress could be eliminated by a self-compensation mechanism. Therefore accurate d33 coefficient was measured for both bulk and thin film piezoelectrics, as was indicated by calibrations using laser interferometry and the Berlincourt method. The d33 coefficient of sol-gel derived PZT films with compositions near the morphotropic phase boundary was measured. The effect of film thickness, preferred orientation, and composition on the d33 characteristics was investigated. The influence of the mechanical boundary condition on the effective d33 coefficient of PZT films was also demonstrated.;The domain wall motions and their contributions to the dielectric and piezoelectric properties of PZT films was investigated. To separate the intrinsic and the extrinsic dielectric responses, measurements at 4K were made to freeze the domain wall motions. The extrinsic contribution to the piezoelectric properties in PZT films was investigated by studying the stress and electric field dependence of the piezoelectric coefficients. In addition, though studying the influence of uniaxial stress and dc electric field on the dielectric properties, both the ferroelectric and ferroelastic activities of the non-180° domain walls in these films were evaluated. At room temperature, 180* domain wall motion was found to be present in all the films, and it increased with increasing film thickness and grain size. However, non-180° domain wall motion was significantly limited in fine grained PZT films, resulting in small extrinsic contribution to the piezoelectric properties. It was also found that the activity of the ferroelastic domain walls increased with the grain size of the film, suggesting a small degree of domain wall pinning in coarse grained films. Finally, the domain structures was studied us transmission electron microscope. |
