Invited
Novel design of flexible piezoelectric materials using a 3D hierarchic porous graphite

Nowadays, piezoelectric materials are widely employed in sensing and energy harvesting, because of their ability to transform mechanical energy into electrical stimuli. Piezoelectric composites combine mechanical flexibility and strong electromechanical coupling constants; however, the low dielectric constant of the polymer and the non-continuity of the ceramic may hinder polarization. The low connection between the piezoelectric particles may be addressed using conductive carbon nanoparticles, but the low connection between the piezoelectric phase is left unanswered. Innovative, highly porous 3D carbon networks may overcome these issues. In this work, it is presented an entirely original paradigm in the design and scalable fabrication of high-performance piezoelectric flexible materials enabled by hierarchic porous graphite. A 3D graphite network was filled with barium titanate and impregnated with a flexible polymer through two distinct bottom-up methods: hydrothermal and sol-gel syntheses. With the hydrothermal method, the influence of various reaction times on the tetragonality of the particles was studied to perfect a hydrothermal (conventional and microwave-assisted) barium titanate synthesis. With the sol-gel method, the sol is infiltrated on the carbon structure, and a heat treatment capable of forming tetragonal barium titanate while not degrading the carbon template is attempted. The structural phase was assessed using X-ray diffraction and Raman spectroscopy, while the morphology was assessed using SEM. The hydrothermally synthesized particles were used in an optimized water suspension with and without voltage to impregnate barium titanate particles into the graphite foam. The final device required a chitosan/zein polymer to include the resultant apparatus with built-in electrodes to test the device’s electrical output. PFM was used to assess the particles’ piezoelectric response following impregnation. The structure : piezoelectric output relationship was exploited in both approaches.


Acknowledgements: This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC). Projects NANOTRONICS (IF/00300/2015); PIEZOFLEX (UTA-EXPL/NPN/0015/2019), FLEXIDEVICE (PTDC/CTM-CTM/29671/2017) are also acknowledged.