In the wake of rapid technological advancements, portable electronics and wireless sensors have driven the need for small, long-lasting power sources. Complex architected porous ceramic structures are relevant for such applications, as these architected, hierarchically organized structures can enhance the functional properties of electroceramic materials. Capillary suspensions (CapS) are a novel, innovative, and inexpensive method for creating highly open porous ceramics. Manufacturing precise porous structures with complex geometries are challenging. However, additive manufacturing of CapS has the potential to develop hierarchically complex structured functional materials with unprecedented properties. A high Figure of Merit (FOM) opens up a wide range of applications ranging from electromechanical energy harvesting over battery and fuel cell electrode materials or thermoelectric applications to bone tissue engineering utilizing piezoelectric stimulation of tissue growth.
 

This work aims to produce highly porous barium titanate (BT) ceramics via direct ink writing using CapS-type BT inks. Various geometries with self-organizing particle networks were printed and analyzed. The capillary forces acting in this ternary solid/fluid/fluid system induced the formation of a self-organized, sample-spanning particle network. Due to the distinct flow properties of the ink, it was possible to achieve printed structures with a high strut size?to?pore ratio of about 1:4, with an overall porosity in the range of 40-60%. Out of all the different geometries tested, the highly porous additive manufactured log-pile structure sintered at 1150 °C was found to show an overall porosity of 58% with the d_33rem value of 330 pC N⁻¹ and a remanent relative permittivity of 1197 which resulted in a high energy harvesting figure of merit (FOM₃₃) of 10.3 pm² N⁻¹, which is more than four times higher than the documented data for this particular material¹. 
 

1. Menne, D., Lemos da Silva, L., Rotan, M., Glaum, J., Hinterstein, M. & Willenbacher, N. ACS Appl. Mater. Interfaces 14, 3027–3037 (2022).