The Project NOLEAD - Motivation



International efforts in removing toxic substances from everyday applications are increasing. The EU passed the "Waste Electrical and Electronic Equipment" (WEEE) and "Restriction of the use of certain Hazardous Substances in electrical and electronic equipment" (RoHS) in 2003[1]. While the WEEE regulates the disposal, reuse and recycling of the mentioned equipment, the RoHS is a necessary requirement to ensure this can be accomplished safely without endangering the environment or people´s health. Mercury, cadmium, hexavalent chromium, the flame-retardants PBB and PBDE and, the focus of this work, lead, have been identified as a primary risk during recycling, disposal or just improper use.

Therefore, as of June 2006, any products introduced to the open market may not include more than 0.1 wt.% of any one of these substances with the exception of cadmium where the limit is even lower than 0.01 wt.%. Currently, an exemption is made for piezoelectrics. However, known lead-free piezoceramics are not yet good enough to replace lead containing materials. While this exemption currently holds for almost all piezoelectric components on the market, this is subject to regular review. New applications using these materials can only be introduced if "elimination or substitution ... is technically or scientifically impracticable, or where the negative environmental, health and/or consumer safety impacts caused by substitution are likely to outweigh the environmental, health and/or consumer safety benefits"[1]. This would for example likely not hold for the use of lead in newly invented consumer electronics. It is, therefore, desirable to find alternatives to the currently market-dominating lead containing piezoelectrics in all current or future applications.

A significant research effort into lead-free alternatives to PZT began a little over ten years ago even though the base materials have been known for more than half a century[2,3]. The research activities before 1990 mostly aimed at searching for the systems, whose properties are better than those of PZT. Increased Curie temperature or polarisation is often desirable for example. However, this was not meant for environmental protection but merely a search for the systems with improved properties over PZT. Since about 1990, the search has mostly directed to improving the already known lead-free materials to the point where they might reach PZT-like properties due to before-mentioned legislation.

In this project we study sodium potassium niobate (NKN) with the aim to replace PZT in future piezoelectric/ferroelectric devices. The thin films are realised via Pulsed Laser Deposition.

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