Prospective Article 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% Nb 2 O 5 , 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, PbZr x Ti 1-x O 3 , (PZT) have held sway in numerous applications (automobiles, microphones, sonar, resonators, medical imag- ing/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 substi- tutes. 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 (K x Na 1-x NbO 3 or KNN here- after) 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 to change. [9] Consequently, for mate- rial substitution to be viable: (i) the benefit of implementing a novel and untested material must be worth the risk of abandon- ing the well-established current materials; (ii) the cost of substi- tution must not exceed the overall benefits; (iii) the costs of renovating production equipment and processes is acceptable; (iv) the implications of substitution are manageable in a wider systems context; and (v) institutional, legal, social, and environmental consequences can be overcome. Aimed at addressing this techno-economic challenge for KNN versus PZT, the latest findings by Ibn-Mohammed et al., [10] published by the Royal Society of Chemistry in the “Energy and Environmental Science” Journal, illustrate the danger of hasty assumptions about “green” credentials by considering only use- phase toxicity. The piezoelectric effect was first demonstrated in the semi- nal work of the Curie brothers [11] in crystals such as quartz, Rochelle salt, and tourmaline, which were shown to convert mechanical to electrical energy and vice versa, giving rise to sensing and actuating applications. [12] A string of ground breaking research advances have subsequently been reported, encompassing synthetic polycrystalline ceramics, single crystals, and thick/thin films, and resulting in a year on year increase in piezoelectric applications. [13] A recent study estimated the global market for piezoelectric actuators alone to be nearly US$7 bil- lion, with a growth rate of 13% per annum. [14] MRS Communications (2017), 7,1–7 © Materials Research Society, 2017. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. doi:10.1557/mrc.2017.10 MRS COMMUNICATIONS • VOLUME 7 • ISSUE 1 • www.mrs.org/mrc ▪ 1