Nanoscale characterization of polycrystalline ferroelectric materials for piezoelectric applications

In this work, the nanoscale electromechanical properties of several important piezoelectric materials [as exemplified by PbZr _x Ti _1-x O₃ (PZT)] suitable for both bulk actuator and microelectromechanical system (MEMS) applications are reported. The investigations are performed by the piezoresponse force microscopy (PFM) that is currently the most suitable tool for both ferroelectric domain imaging and local piezoelectric studies. The local piezoresponse of individual grains is measured in PZT films and compared with average piezoelectric behavior. Frequency dependencies of local piezoelectric coefficients are presented and analyzed. The results on local piezoelectric nonlinearity, as well as on nanoscale fatigue and aging are briefly discussed. These measurements demonstrate that PFM is promising for studying local piezoelectric phenomena in polycrystalline ferroelectrics where defects and other inhomogeneities are essential for the interpretation of macroscopic piezoelectric properties. Finally, local electromechanical properties of polycrystalline relaxors (PMN-PT, PLZT, doped BaTiO₃) are briefly outlined.