Speaker
Description
Organic ferroelectrics are important functional materials for their flexible structure, low cost and applications in quantum computing, energy storage materials, electronics and medical devices [1-2]. These materials are free from toxic elements and so sustainable alternatives to traditional ferroelectrics. Most of these organic ferroelectrics are either hydrogen bonded or halogen bonded, which play an important role in their ferroelectric properties [3-8]. Charge or proton transfer occur through chemically distinct donor-acceptor pairs connected through these bonds, which act as a bridge. In presence of an external field this transfer of protons changes the polarisation of these materials by changing geometry from centro-symmetric to non-centrosymmetric [2]. Microscopic understanding of the ferroelectricity, particularly dynamics of these hydrogen and halogen bonds are yet to be reported.
In this presentation we investigate some of these ferroelectrics, both hydrogen bonded and halogen bonded, such as croconic acid and 4,5-¬‐dichloro-¬‐2-¬‐methyl-¬‐imidazole (C4H4Cl2N2), respectively. The results of quasi-elastic and inelastic neutron scattering experiments will be compared with first-principles molecular dynamics and lattice dynamics simulations. It is found that strong anharmonicity present in both hydrogen and halogen bonds in these materials. Calculated Born effective charge tensor predicts that microscopic origin of ferroelectricity of this material is from H bonding of either O-H—H or N—H-N bonds forming bridges between molecular units.
We will present microscopic insight of the dynamics of this material using both INS and QENS spectroscopy complimented by first principles molecular simulations. The prospect of using machine learned potentials will be discussed.
[1] S. Horiuchi et. al, Nat. Mat. 7, 267 (2008).
[2] S. Horiuchi et. al, Nature, 463, 789 (2010).
[3] S. Mukhopadhyay et. al., Phys. Chem. Chem. Phys., 16, 26234 (2014).
[4] S. Mukhopadhyay et. al., Chem Phys., 427, 95, (2013).
[5] S. Mukhopadhyay et. al., Phys. Chem. Chem. Phys., 19, 32147 (2017).
[6] S. Mukhopadhyay, J. Phys. Comm., 3, 113001 (2019).
[7] S. Mukhopadhyay, Front Phys, 10, 834902 (2022).
[8] M. Owczarek et al. Nature Commn, 7, 1308 (2016).
