Nondestructive Characterization of PZT Materials for Sensor and Actuator Applications

The conventional ultrasonic time-of-flight technique is employed showing that the sound propagation in a poled piezoelectric ceramic is anisotropic. The sound velocity depends on three directions, the direction of sound propagation, the wave polarization and the direction of electrical poling of the ceramic. To understand the macroscopic behavior of the piezoelectric material, knowledge of the microscopic structures and processes is required. Two techniques are presented to image ferroelectric domains in commercially available piezoceramics. Indirect imaging can be achieved if, after selective chemical etching, the samples are scanned by means of a conventional AFM. Individual grains, subgrains, and domain formations were imaged with this technique on ceramics with three different compositions. Using an electrical conductive sensor tip in the AFM, the domains were individually excited to mechanical vibrations due to a field locally exerted by the tip. The domains form a contrast obviously depending on their orientation relative to the externally applied electrical field. We also employ a new method, the contact resonance spectroscopy based on Atomic Force Acoustic Microscopy (AFAM) to measure elastic properties of piezoelectric ceramics. There, the AFM sensor is elastically indented into the sample surface at megahertz-frequencies and from the cantilever response, the Young's modulus can be derived. Using this technique, we expect to quantitatively determine the elasticity of differently oriented ferroelectric domains.