Strain Dependent Properties, Intercalation and Adsorption Studies of Graphene Like Two Dimensional SiC and SiB

Abstract

This thesis reports the variation in properties of graphene like two dimensional materials SiC and SiB with the application of strain and their properties in being the anode of rechargeable Li-ion batteries. The material was modelled and the calculations were carried out using Density Functional Theory (DFT) using Vienna Ab-initio Simulation Package (VASP) and Quantum Espresso packages. SiC in its pristine case showed isotropic behaviour but the inducing of stress changed it to anisotropic behaviour. On the other hand, SiB was anisotropic in its pristine form and anisotropic behaviour increased with the application of strain. Both the structures were mechanically stable satisfying the Born criteria. The mechanical behaviours showed highly non-linear nature for the case of SiB and the ultimate stress were much higher than their counterpart silicene. The application of strain specifically biaxial onto SiB generated a new structure having a planar architecture very similar to graphene. The experimental synthesis of SiC urged to check its potential in being the anode of Li-ion batteries. Pristine SiC was a poor candidate and was introduced with defects to check for improvement in properties for an anode. Bi vacancy defective configurations showed an interesting characteristic upon optimization. There was a transition from point to topological type of defects forming 5-8-5 rings in the case of C-bi vacancy and Si-C bi vacancy and it was a Li mediated transition in the case of Si-bi vacancy configuration. Among the various defective configurations, Stone-Wales (SW) defective configuration was found to be the best candidate having lowest value of binding energy compared to all the other configurations. The characteristics of SW configurations are specific capacity 501 mAh/g, open circuit voltage 0.11 V, diffusion barrier 0.57 eV which is in accordance with the electrochemical characteristics in being the anode of Li-ion batteries. Therefore, SW defective configuration was proposed to be a prospective candidate for the next generation Li-ion batteries.