| The superhard materials Fe-B and C-N have potential applications in mechanical properties.There has been a shortage of study on optical properties while many theoretical calculations and experimental investigations focusing on mechanics,magnetism,and electricity appeared in the past few decades.Given this,based on the first-principles,we study the optical properties of Fe-B and C-N structures with many-body perturbation theory and density functional theory,respectively.With GGA+PBE methods,we study the electronic structure of tP10-FeB4,I41/acd-FeB4,and oP12-FeB2,and further calculate their optical properties with GW+BSE methods.It shows that oP12-FeB2 has a small energy gap and a high absorption peak in the visible light region.It can be used as high hardness absorption material in the visible light region.But for tP10-FeB4 and I41/acd-Fe B4,larger energy gap and low orbit occupation on both ends of band gap make them have high absorption not in visible light but in the ultraviolet region.Based on DFT,we carry out the calculation on the C-N system with GGA+PBE methods.The crystal structure parameters,electronic transition mechanism,the cause of dielectric peaks and their optical properties are concretely analyzed.According to the difference between the optical characteristics of eleven structures and high hardness themselves,we also take preliminary forecast for the potential application.In the last part,we study the Ti-doped I2d-CN2 to improve optical properties of the I2d-CN2 structure.Based on the different doping methods and concentrations,we concretely analyze crystal parameters,electronic structures,optical and mechanical properties.It is found that the way in which N is substituted by Ti atom has better behaviors in visible light absorption and Vickers hardness than the way in which C is substituted by Ti atom.We also find that the best concentration is 6.25%,in which the structure still belongs to the high hardness material.It provides a certain basis for follow-up study. |
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