Periodic Reporting for period 2 - MemoMOFEnergy (Constructing polar rotors in metal-organic frameworks for memories and energy harvesting)
Reporting period: 2019-07-01 to 2020-12-31
As ferroelectrics can store and switch their polarity, they can be used as memories. Via the piezoelectric effect, they can harvest mechanical vibrations. The materials most compatible with flexible substrates, are soft matter materials. However, these so far don’t meet the requirements. Especially lacking is a combination of i) polarisation stability, ii) a sufficiently low energy barrier for polarisation switching and iii) fast switching. As energy harvesters, soft matter materials are hampered by low piezoelectric coefficients.
The main objective of this proposal is rational design of ferroelectrics by obtaining a fundamental understanding of the relation between structure and properties. I will achieve this uniquely by synthesizing polar rotors into 3D crystalline scaffolds that allow to alter the rotors’ nano-environement. I will achieve this via polar ligands in metal-organic frameworks (MOFs). The variability of MOFs allows to tune the nature of the hindrance towards rotation of the polar rotors. The tuneable flexibility allow to regulate the energy harvesting efficiency. Moreover, MOFs have already shown potential as biocompatible materials that can be integrated on physically flexible substrates.
The research consists of i) synthesis of polar rotor MOFs with targeted variations, ii) reliable characterisation and computational modelling of the electronic properties, iii) nanoscopic insight in the switching dynamics. The approach allows to understand how ferro- and piezoelectricity are related to the materials’ structure, and hence to develop materials with exceptional performance.
Metal-organic frameworks can have highly mobile linkers. For our goal of ferroelectric metal-organic frameworks, collective motion of these linkers is of paramount importance. Via a combination of experimental and computational work we could for the first time identify the emergence of cooperative linker motion in metal-organic frameworks.
With regard to methodology, we expect to have developed new methods for the characterisation of the shear component ofpiezoelectricity based on piezo-force microscopy, and to be able to detect fast ferroelectric switching via optical methods. We expect to develop computational methodology that allows for unravelling the correlated motions of MOF-linkers on larger length scales.