Properties of Lead-Free Piezoceramics Based on Alkali Niobates

The market for piezoceramic components is dominated by lead zirconate titanate (PZT) materials containing more than 60 wt% lead. Since lead is a toxic heavy metal, it has become a great concern how to eliminate the use of PZT by replacing it by non-harmful materials while maintaining comparable piezoelectric properties. This was the objective of the European LEAF project within the GROWTH programme, ending in February 2004. In this project, alkali niobates were proposed as alternative piezoceramic materials, and special emphasis was given to potassium sodium niobate, (K,Na)NbO ₃ . Among the interesting properties of this system is a low theoretical density, leading to a relatively low acoustic impedance of 24 MRa. The partners of the project have developed lead-free ceramics based on potassium sodium niobate that can be a competitive alternative to PZT for certain applications. A selection of obtained properties, examples of industrial applications and an overview of end-user considerations will be presented. Furthermore, some considerations on the origin of even harmonics in the impedance spectrum, as seen in certain KNN ceramics will be given.

Keywords:

• KNN
• K_0.5Na_0.5NbO₃
• lead-free
• even harmonic modes
• LEAF

Acknowledgments

The LEAF project consortium consisted of 8 partners besides Ferroperm Piezoceramics A/S, all of whom have made valuable contributions to the project results, and the authors wish to express their thanks to the following.

Prof. Marija Kosec and Dr. Barbara Malic, Jozef Stefan Institute (esp. development of doped compositions and processing); Dr. Dragan Damjanovic, Dr. Abdolghaffar Barzegar and Dr. Marlyse Demartin Maeder, LC-EPFL (esp. dielectric and piezoelectric characterisation); Dr. Lorena Pardo, ICMM-CSIC; Dr. Christian Pithan, EKM-FZJ (esp. microscopy, sinter forging, impedance spectroscopy); Dr. Guy Feuillard, GIP Ultrasons (esp. simulation of transducers); Mr. Frank Tichy and Mr. Harald Klaveness, Simrad AS; Prof. Hans W. Persson, Ceram AB (esp. demonstrator for liquid-level measurement); Dr. Michael Platte and Dr. Michael Lach, Karl Deutsch Prüf- und Messgerätebau GmbH.

This work was supported by the European Community through the GROWTH Programme (FWP5), Contract No. G5RD-CT2001-00431.