The general objective is to replace existing PZT based ceramics with alternative technologies, such as lead-free piezoelectric materials (aspiring to have no reduction in performance levels with even the potential for a gain), which will be suitable for
military underwater applications, including the most demanding, which is a passive hydrophone and active transducer for sonar and underwater communications. The overarching goal is to have the emergence of at least one European lead-free
piezoceramic supply chain, which will soon be mandatory with regarding the European REACH regulations. The patenting of new formulations and processes would be of use for sonar applications.

PZT ceramics are used in most acoustic sensors for underwater military applications: hydrophones, sonobuoys, dipping sonars, variable depth and hull mounted sonars, torpedoes, towed arrays. With the launch of major fleet renewal programs, which are currently entering the implementation phase, the R&D of the naval sector has the challenge to control the environmental impact and the safety of ships, while preserving acoustic performance.

Since the renewal of scientific work on the replacement of PZT, started around 2000, considerable research has been conducted in studying substitution ceramics, with promising results. Research on demonstrators integrating lead-free piezoelectric
ceramics and crystals based on BT34, KNN35, KN36, BCTZ37 has been published in scientific literature. However, gathering all the properties of PZT materials to alternative lead-free piezo-electric materials has never been done, and this is the
reason academic research is still extremely active in this sector. In addition, reproducibility and process up-scale raise numerous issues.

Apart from military sectors, civilian markets are very broad and extend to several domains (non-destructive control sensors, medical echography apparatus, automotive, printing, energy harvesting). Even if civilian markets are very broad and
potentially less demanding in terms of physical and piezoelectric properties than military domains, very few lead-free piezoelectric materials are proposed at industriallevel and their physical and piezoelectric properties are very far from PZT. This means that mastering the production of advanced and high performance lead-free piezoelectric materials at an industrial level remains challenging. For the time being, no lead-free solutions exist that facilitate the high level of performance required by
military underwater applications.