Crystal Engineering of Organic Plastic Crystals: Applications in Barocalorics, SHG, Piezoelectricity and Ferroelectricity

Mondal, Amit (2023) Crystal Engineering of Organic Plastic Crystals: Applications in Barocalorics, SHG, Piezoelectricity and Ferroelectricity. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Amit Mondal (15IP010)) 15IP010.pdf - Submitted Version Restricted to Repository staff only Download (28MB)

Abstract

Harnessing the exceptional efficiencies offered by single-crystal-based optical, electrical, magnetic and ferroelectric materials becomes nearly impossible for use in devices, particularly in the flexible variants, owing to their brittleness. While brittle crystals’ tendency to crack on mechanical impact greatly limits their durability in the devices, rigidity makes any post-crystallization reconfiguration unthinkable, for instance moulding them into desired three dimensional shapes. However, there have been various reports in last two decades demonstrating mechanical adaptability in organic molecular crystals, which include 1D and/or 2D plastically bendable or hand-twisting crystals, mechanically shearing crystals and elastically flexible crystals. But, none of them show any 3D plasticity, i.e., ductility and malleability similar to the malleable metals. In this regard, the 2nd Chapter, covers metal-like ductility and malleability in two isomorphous borane amine (BR3NMe3; R = H/F) plastic crystals (PCs) and highlights the role of dihydrogen bonding in the mechanical property of BH3NHMe2 which negates ductility in spite of globular molecular shape similar to BR3NMe3 systems. Chapter 3 includes the work hardening (also called strain hardening) and strain rate hardening behaviours observed in some organic PC systems, which was confirmed from their stress-strain curves (extracted from the partial loading-unloading nanoindentation experiments) and strain rate sensitivity analysis, respectively. My 4th Chapter presents the first correlation study among crystal packing, total intermolecular interaction energies (Etotal) and the mechanical properties [hardness (E) and modulus (H) values] with entropy change (ΔSt) of the order-disorder phase transition and the phase transition temperature (Tt) of some barocaloric organic PCs which have gained recent interest as solid state coolants as a promising alternative for harmful CFC based refrigerants. Besides, we have performed temperature dependent SHG ON-OFF switching studies by exploiting the non-centrosymmetric structures of some of the PCs. In Chapter 5, I have presented multiaxial ferroelectricity in some single component based neutral organic PC systems along with their piezoelectric energy harvesting ability by demonstrating some real-life applications like LED lighting and capacitor charging. Also, we have explained their piezoelectric behaviours from crystal engineering point of view i.e. by a comparative study of their polarization charge density and quantitative mechanical properties like E and H. In short, I have explored the mechanically soft organic plastic crystal systems for diverse applications in barocalorics, SHG, piezoelectricity and ferroelectricity.

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