Lead-free piezoceramics: From basic science to application

While the traditional materials of choice for piezoelectric devices over the past 60 years were lead-based perovskite ceramics, the environmental- and health-concerns, supported by governmental regulations, triggered the search for new lead-free alternatives. During the past 10 years the research output rose from 10 to 400 publications per year with China and Japan leading, Europe accounting for 10 % of the total quantity and the US only showing very select activities. In addition, a number of companies invested large sums into research and they aim at solid financial return. Some of them produced material reproducibly in 100 kg batches and select areas were identified, where lead-free piezoceramics have an advantage to lead-containing piezoceramics. As a result, the first products started to appear at the market place.The aim of this contributions is to review the global situation and present scientific challenges and advancements, which have been made by introducing the three main competitors based on different chemistry and different salient phase diagrams. It is now apparent, that lead-free piezoceramics will come, but with different potency for the different applications concerned. I will specifically highlight significant recent discoveries in the field of NBT-BT composites. They allow to reduce the electric driving field, enhance the depolarization temperature and provide a new means of making the material harder.