Engineered growth of polycrystalline amino acids for eco-friendly piezoelectric device components Suman Bhattacharya†, Krishna Hari†, Geetu Kumari† and Sarah Guerin* Department of Physics and Bernal Institute, University of Limerick, Castletroy, Limerick, V94T9PX, Republic of Ireland Email: sumans.bhattacharya@ul.ie ; sarah.guerin@ul.ie †Authors contributed equally. Piezoelectricity is the ability of certain class of materials to generate an electric voltage on the application of mechanical stress, or conversely undergo mechanical deformation in the presence of an electric field. Traditionally known piezoelectric materials, e.g. , quartz (1.4 pC/N), aluminium nitride (AIN; 8 pC/N) and lead zirconium titanate (PZT, 350-500 pC/N), though highly efficient in their performance, suffer from the inherent disadvantages of being non-environmentally friendly, lack designability, and offer less structure-property control. Hence, a paradigm shift has occurred in the area of piezoelectrics in the last two decades towards the use of organic and particularly bioorganic materials 1 , as potential alternatives to traditional inorganic and Pb-based piezoelectric materials. Diverse bioorganic materials, e.g. , wood, bones, fibrous proteins, DNA are known to exhibit piezoelectric behaviour. 2 To exhibit this piezoelectric property, it is necessary for a material to be non-centrosymmetric or chiral, which makes the naturally occurring amino acids, an automatic choice for the study as potential piezoelectric systems. 1a,3a Among the 20 naturally occurring amino acids, 19 amino acids crystallise in chiral space groups, and are potential piezoelectric materials. Further using crystal engineering principles, a possibility of generating diverse chiral multicomponent 3b,c crystals systems based on the chiral amino acids, e.g. , cocrystals and salts, opens the door for designing future materials with target piezoelectric properties, with modified structure and stability. Herein, a structure-property study is presented, co-relating the piezoelectric performance of amino acid based systems, with their crystal structure. Both single component amino acid crystals and multicomponent amino acid systems (amino acid cocrystals, inter-amino acid cocrystals, and amino acids salts) are employed for the study. The Cambridge Crystallographic database is searched for amino acid systems, which are known to form crystals with needle and blocked shaped morphology. The morphology search is performed, to identify systems, which offer better control on crystal orientation. As piezoelectricity is an anisotropic property, DFT calculations are used to predict the optimal orientation axis for maximum electrical output under an applied force. Thin films of selected systems are prepared on suitable conductive substrates, and the observed piezo measurements are correlated with the inherent chemistry of the crystal structures. The present study will generate useful insights for the future designing of environmentally friendly biological piezoelectric systems, for real-life application in the development of piezoelectric devices. References 1. (a) Lemanov et al . Ferroelectrics 2000, 238 , 211. (b) Guerin et al. , NPG Asia Mater 2019, 11 , 10. 2. (a) Fukada et al. , Ultrason., Ferroelectr., Freq. Control, IEEE Trans. 2000, 47 , 1277. (b) Fukada et al. , J. Phys. Soc. Jpn. 1957, 12 ,1158. (c) Fukada et al., J. Phys. Soc. Jpn. 1955, 10 ,149. 3. (a) Guerin et al., Cryst. Growth Des. 2018, 18 , 4844. (b) Guerin et al. , Cryst. Growth Des. 2021, 21 , 10, 5818. (c) Wei et al. ACS Nano 2020, 14 , 10704.
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