Theoretical and Experimental Investigations of Bending and Piezoelectricity in Organic Molecular Crystals

Chowdhury, Rituparno (2021) Theoretical and Experimental Investigations of Bending and Piezoelectricity in Organic Molecular Crystals. Masters thesis, Indian Institute of Science, Education and Research Kolkata.

Text (MS Dissertation of Rituparno Chowdhury (15MS028)) 15MS028_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (6MB)

Abstract

The regularity in crystals allows us to determine and study anisotropic or direction-dependent properties such as semi-conductivity, piezoelectricity, ferroelectricity, mechanical modulation, etc. In molecular crystals this dependence is caused by direction-dependent interactions or bonding patterns which heavily influence the local electronic states and their respective energy differences as well. However, this ordered nature of crystalline matter predisposes most people to assume that crystals are highly rigid and cannot be bent, bending them would lead to fracture since they will have a short elastic limit prior to yielding. But this is not the case! In 2005 a seminal study by Reddy et al [1] showed crystals which were engineered at a molecular level such that they pack in planes, these planes could slide over each other easily resulting in a macroscopically observable, and easily performed, shear deformation which is shown in Fig 1.a, shockingly enough despite deformation such deformed crystals would still diffract implying that they were still crystalline. This model and it’s features were largely confirmed in a systematic crystallographic investigation of CAF:CNB:MeOH Cocrystals by senior members of our laboratory which are currently being prepared for publication. The model proposed by Ghosh et al suggest conservation of long range order and some preliminary observational and crystallographic proof of their model is provided

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