Investigation of structural and electronic properties of super hard materials with density function theory

In this dissertation, theoretical and experimental measurement of hardness, hardness measurement methods, the main factors affecting the microscopic hardness and basic properties of hardness, are investigated by using the density functional theory (DFT) and ab-initio pseudopotential method within the local density approximation (LDA). To do this, we used the c-BN, t-BC2N and h-BC5 compounds which are previously known as super-hard materials.We relaxed these three compounds and calculated the microscopichardness of compounds, respectively. We identified the factors that can affect the hardness using theresults of calculations.We calculated that the hardness of the c-BN, t-BC2N and h-BC5 compounds is larger than 40 GPa.According to the calculation results, we found that these compounds are super-hard materials. We compared thesecompounds with diamond structure which is known as the hardest compoundin nature and obtained the basic factors affecting the hardness. These basic factors are short bond length, high density and high covalent bond number. Thanks to those factors, we showed which parameters can be taken into account for the synthesis of super-hard material.Key Words: Microscopic hardness, super hardness, c-BN, t-BC2N- h-BC5