Researchers find large piezoelectric effect in organic crystal

December 05, 2017 // By Nick Flaherty
Researchers at the University of Limerick (UL) in Ireland have discovered an organic compound that generates electricity when tapped or squeezed in a similar way to today's inorganic piezoelectric materials. This opens up the possibility of biodegradeable and implantable energy harvesting sources.

The team at UL's Bernal Institute have discovered that the biomolecule glycine, when tapped or squeezed in crystal form, can generate enough electricity to power electrical devices. They have applied for a patent for using this technique to power medical devices.

The piezoelectric effec in biomolecures is typically very low, in the range of 0.1–10 pm/V. The team used computer modelling to find a high shear piezoelectricity of 178 pm/V in beta (β) glycine crystals which is of similar magnitude to barium titanate or lead zirconate titanate. The highest predicted piezoelectric voltage constant for the β-glycine crystals is 8 V/mN. This comes from an efficient packing of the molecules along certain crystallographic planes and directions.

Glycine is the simplest amino acid and one of the building blocks of DNA, occuring naturally in almost all agricultural residues. This means it can be produced at less than one per cent of the cost of piezoelectric ceramic materials and can easily scale to produve the energy required for devices. 

"It is really exciting that such a tiny molecule can generate so much electricity," said Sarah Guerin, a post-graduate student at the Department of Physics and the Bernal Institute. "We used computer models to predict the electrical response of a wide range of crystals and the glycine number was off the charts. We then grew long, narrow crystals of glycine in alcohol," she added, "and we produced electricity just by tapping them."T

The predictive models saves years of trial-and-error lab work says the team. The modelling data identifies what kinds of crystals to grow and where best to cut and press those crystals to generate electricity.

"We also have a pending patent that translates our findings to applications such as biodegradable power generation, devices detecting diseases inside of the body and physiologically controlled drug pumps," said Professor Tofail Syed, Science Foundation Ireland (SFI) Centre for Medical Devices (CURAM) investigator.

The research was published on December 4, 2017 in  Nature Materials .