Are lead-free piezoelectrics more environmentally friendly?
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Are lead-free piezoelectrics more environmentally friendly? T. Ibn-Mohammed, and S. C. L. Koh, Centre for Energy, Environment and Sustainability, The University of Sheffield, Sheffield S10 1FL, UK; Advanced Resource Efficiency Centre, The University of Sheffield, Sheffield S10 1FL, UK I. M. Reaney, and D. C. Sinclair, Departments of Materials Science and Engineering, The University of Sheffield, Sheffield S1 3JD, UK K. B. Mustapha, Departments of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, Malaysia Campus, Selangor Darul Ehsan 43500, Malaysia A. Acquaye, Kent Business School, University of Kent, Canterbury CT2 7PE, UK D. Wang, Departments of Materials Science and Engineering, The University of Sheffield, Sheffield S1 3JD, UK Address all correspondence to T. Ibn-Mohammed, I. M. Reaney at t.ibn-mohammed@sheffield.ac.uk; i.m.reaney@sheffield.ac.uk (Received 16 December 2016; accepted 30 January 2017)
Abstract Considered as a less hazardous piezoelectric material, potassium sodium niobate (KNN) has been in the fore of the search for replacement of lead (Pb) zirconate titanate for piezoelectrics applications. Here, we challenge the environmental credentials of KNN due to the presence of ∼60 wt% Nb2O5, a substance much less toxic to humans than Pb oxide, but whose mining and extraction cause significant environmental damage.
Piezoelectric materials based on lead zirconate titanate, PbZrxTi1−xO3, (PZT) have held sway in numerous applications (automobiles, microphones, sonar, resonators, medical imaging/diagnostics, printers, ultrasonic motors, wearable devices, smart structures, medical implants, etc.) for over 50 years. The dominance of PZT-based ceramics is due to their superior piezoelectric response, which ultimately ensures an unmatched efficiency in the direct interconversion of electrical and mechanical energy. Beyond this superior piezoelectric response, lies a level of toxicity that threatens the position of PZT as the leading piezoelectric ceramic, and has sparked urgent global efforts to identify environmentally benign substitutes. PZT accrues its toxicity from >60 wt% lead oxide (PbO). Pb is a toxic heavy metal that has been the subject of calls for elimination from all consumer electronics and products,[1–6] based on worldwide initiatives for electronic equipment reuse and recycling such as the EU directives on waste electrical and electronic equipment (WEEE) and restriction of hazardous substances (RoHS).[3,7,8] A fundamental issue that emerges with the recognition of PZT’s toxicity is the need to find surrogate materials (with improved eco-friendliness and excellent piezo-activity) in the myriad of products in which PZT plays a major functional role. Potassium sodium niobate (KxNa1−xNbO3 or KNN hereafter) is a potential Pb-free replacement for PZT[4] and for room temperature applications in particular looks promising. Material replacement in existing products has many obstacles,
such as substitution costs, price ratio, and in some instance the end user’s propensity
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