Piezoelectric Biomolecules for lead-free, Reliable, Eco-Friendly Electronics

Project Information

Pb-FREE

Grant agreement ID: 101039636

DOI

10.3030/101039636

EC signature date 2 March 2022

Start date 1 June 2022

End date 31 May 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 499 525,00

EU contribution

€ 1 499 525,00

Coordinated by

UNIVERSITY OF LIMERICK
Ireland

Periodic Reporting for period 1 - Pb-FREE (Piezoelectric Biomolecules for lead-free, Reliable, Eco-Friendly Electronics)

Reporting period: 2022-06-01 to 2024-11-30

Summary of the context and overall objectives of the project

The project aims to make a new eco-friendly class of piezoelectric material technologically viable as a replacement for current commercial materials that use environmentally damaging material components. Piezoelectric materials can convert mechanical energy into electrical energy and vice versa and are used everywhere from advanced medical devices to musical birthday cards. Our objective is to crystallise small biomolecules into any shape and size and protect them from water using thin plastic coatings. All of our materials- the crystals, the polymers, and the electrodes should be biocompatible by the end of the project (for implantable medical device applications), and ideally recyclable or biodegradable. Every piezoelectric sensor needs a top and bottom electrode to collect (or deliver) the electrical signal. Applying electrodes to biomolecular crystals is challenging as they grow chaotically with a lot of roughness, and are hard for materials to adhere to, so a large part of the project involves testing and developing methods for attaching conductive materials to the crystal assemblies.
We are also using computer simulations, based on quantum mechanics, to predict the piezoelectric properties of thousands of existing biomolecular crystals. This will allow us to firstly discover new piezoelectric materials with high performance. It will also allow us to select materials from our very own database for different applications based on, for example, if the sensor needs to be flexible or rigid. With all of this data, we can also train machine learning algorithms to give us design rules for piezoelectricity i.e. tell us what it is about a particular biomolecule or how it packs together in a crystal that makes it highly piezoelectric. Crystallographers can then grow the crystals discovered in the database or use the design rules to make new molecules and crystals. The final step is then to see if artificial intelligence could use these design rules to engineer new molecules that would have giant piezoelectric responses. As this is a relatively new class of materials (for piezoelectric applications) the project also involves extensive characterisation and standardisation of these materials, such as what forces they can withstand and what temperatures they can operate in, which requires specialized or custom equipment.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To date, the project has successfully performed a high-throughput screening of over one thousand molecular crystals and predicted their piezoelectric properties- which includes their mechanical properties and dielectric properties. We have also developed a workflow for predicting the stress-strain curve of these crystals, allowing us to identify properties such as the ultimate tensile strength and the fracture point of crystals without carrying out experiments. We have compiled our database of small molecular crystals and their predicted electromechanical properties into an interactive, online repository CrystalDFT. We provide a statistical analysis of the predicted values, highlighting the broad range of electromechanical properties amongst this primary dataset, and in particular, the high number of crystals that have a naturally occurring longitudinal d33 constant. This longitudinal electromechanical coupling is a prerequisite for several conventional sensing and energy harvesting applications, the presence of which is notably rare amongst the literature on biomolecular crystal piezoelectricity to date.
Experimentally we have developed a method for growing biomolecular crystals as polycrystalline assemblies- meaning multiple crystallites grown together as a cohesive bulk-in any desired shape at cm scale. We have successfully grown polycrystalline amino acid assemblies in a facile, scalable, substrate-free manner. This allows these functional materials to be fabricated into any desired shape and size for sensing, actuation, and energy harvesting applications. We have validated this method on a large number of molecular crystals, including multi-component crystals- where two or more molecules are crystallised together. We have created a method for coating uniform polycrystal assemblies in polymethyl methacrylate (PMMA) that protects them from water- that methodology is now being adapted for samples with high roughness/ complex geometries.
Both our modelling and experimental team have discovered new piezoelectric materials with novel properties and/or high performance. Our engineering team is benchmarking a number of energy harvesting technologies on commercial piezoelectrics whilst also taking on the challenge of electroding biomolecular crystal piezoelectrics in a reliable/repeatable manner. We can also measure the nano and macroscale mechanical properties of our materials, showing how they respond to both small deformations and large direct forces.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

1. We have shown that amino acid polycrystalline assemblies can be grown using an evaporative method onto custom silicone molds so that the resultant bulk assembly can act as a stand-alone component. Compared to ceramic device fabrication, our methodology contains only a few steps starting from weighing the starting materials, mixing to form saturated homogeneous solution, deposition into the mold and subsequent slow evaporation at room temperature, followed by demolding and air drying. Moreover, these eco-friendly piezoelectric elements demonstrate a maximum peak-peak voltage of 1.1 V and can operate at high temperatures.

2. We have achieved successful crystallisation of the multicomponent solid, S-Mand•L-Lys•5H2O, made from two components which have diverse and challenging crystallisation behaviours. This material demonstrates a single crystal d33 piezoelectric constant of 3.5pC/N but a polycrystalline d33 of 11 pC/N at the macroscale due to contributions from shear piezoelectric components induced in the triclinic structure. The brittleness of the crystals (Young’s modulus = 37 GPa) is overcome by reinforcing the substrate-free piezoelectric disc with a thin polymer coating to prevent flaking. DFT-calculated crystal, intramolecular, and intermolecular dipoles substantiate the nanoscale origins of the anisotropic piezoelectric responses.

3. Working with our collaborators, we have crystallised a series of structures sustained by both halogen bonds and hydrogen bonds, that exhibit a considerably high shear piezoelectric response. We have used Density Functional Theory (DFT) calculations to predict, quantify, and rationalise the piezoelectric response of these crystalline materials. Our calculations reveal a high shear piezoelectric response in all three crystals, with the highest predicted response of d15 = 99.19 pC/N. Piezoresponse Force Microscopy (PFM) experiments confirm effective shear piezoelectric constants of 54-74 pC/N. All three crystals belong to space groups that allow for natural longitudinal piezoelectric responses, with experimentally validated single crystal d33 values of 5-10 pC/N. This work adds to the growing number of unpoled molecular crystals approaching triple-digit piezoelectric responses to rival conventional perovskite ceramics.

A variety of shapes and chemistries of molded amino acid crystals for eco-friendly sensing and actua