How to Make Porous Piezoelectrics? Review on Processing Strategies.

Ferroelectric ceramics are a technologically important class of materials that are currently exploited in actuators, sensors, transducers, and memory devices. The introduction of porosity into these materials has been proved to be an effective tool for tuning functional properties for specific applications, such as piezoelectric and pyroelectric devices and energy harvesters. In this review, a comprehensive description of the most widely used processing techniques able to produce porous ferroelectric ceramics is reported. In particular, the state-of-the-art production strategies including replica technique, direct foaming, sacrificial template method, and additive manufacturing used up to now for the realization of porous piezoelectric lead zirconate titanate (PZT)-based structures are critically reviewed and rationalized. Moreover, this work aims to give concrete indications on the more effective and actual production strategies that should be exploited for the development of porous PZT-based materials for the specific applications. Finally, two case studies are reported to remark the critical importance of material-processing-microstructure correlations on the functional properties of the designed devices.