Leadfree Piezoceramics for Actuators
|roject manager:||Prof. Dr.- rer. nat. Gerold A. Schneider|
|Projekt worker:||M. Sc. Rodrigo Pacher Fernandes|
|Supported by:||BMBF 08-001 Realisierung eines leistungsfähigen bleifreien Vielschicht-Piezoaktors über einen mehrskaligen Entwicklungsansatz - RealMAK|
|Collaboration:||Siemens AG München, Robert Bosch Stuttgart, IKM Universität Karlsruhe, IKTS Fraunhofer Dresden, Max Planck Institute for Metals Research, PI Ceramics|
PZT (Lead zirconium titanate) is nowadays widely used as a piezoceramic actuator e.g. Piezo-Inline-Injektor of a Common-Rail-Diesel (figure 1). Since the “Directive 2002/95/EC of the European Parliament and of the Council” has been released on the restriction of the use of certain substances (for example lead) in electrical and electronic equipment on 27.01.2003, the search for leadfree piezoceramics has been intensified within the European Union and beyond. The directive states that the use of lead in special applications among them piezoceramic devices is still allowed, but only till an adequate leadfree substitute is found. Therefore, anyone within the ceramic industry, who can supply a piezoceramic with properties close to PZT, will have a great advantage in international competition.
Fig.1: Piezo-Inline-Injektor of a Common-Rail-Diesel
Our group have different tasks in the project: the main topic is the characterization of the domain structure of the new materials with the Piezoresponse Force Microscope (PFM). This technique allows us to image domain structures down to a few nanometers. The PFM also enables the study of the switching behaviour of these new materials. As an example, in figure 2, the domain structure of potassium sodium niobate (KNN) after the sample was exposed to different electric fields. The remnant domain structure was imaged after each increasing step in the electric field.
Fig. 2: The domain structure of potassium sodium niobate (KNN) after the sample was exposed to different electric fields
Other tasks in the project:
Investigation of the aging and fatigue behaviour of actuators:
- Using PFM to image the domain structure after the actuator is exposed to a cycling electric field.
Local characterization of the ceramic-electrode interface:
- With Kelvin Force Microscopy (KFM) it is possible to image the influence of a possible second phase in the ceramic layer due to diffusion from the electrode.
- Using our 4-point bending machine we can grow a crack in a controllable manner in the ceramic-electrode interface for the determination of the interface fracture toughness.
R.P. Herber, G.A. Schneider, Susanne Wagner, Michael J. Hoffmann: Characterization of ferroelectric domains in morphotropic potassium sodium niobate with scanning probe microscopy. Applied Physics Letters 90, 252905 (2007)
Ralf-Peter Herber, Christian Schröter, Berit Wessler and Gerold A. Schneider
High throughput screening of piezoelectric response of ferroelectric thin films with automated scanning probe microscopy, Thin Solid Films, Article in Press, Corrected Proof