Electronic Structure And Optiacal Properties Of Cr₂AlC And Ti₂SnC From First Principles

Cr₂Al C and Ti₂SnC are new layered ceramics with excellent overall performance including both metal conductivity and strong resistance to high temperature and thermal stability and other special properties.These properties determine their function and structure can become potential high quality ceramic materials.Based on the density functional theory?DFT?,the electronic structure and optical properties of Cr₂AlC and Ti₂SnC were calculated by the first principle calculation software.In this paper,the dielectric constant,absorption coefficients,reflectance,photoconductance,refractive index and loss function of the two substances were calculated by calculating the energy structure and density of the two materials.The intrinsic relationship between the electronic structure and the optical properties is analyzed.The energy band structure and the density of states are obtained by calculating the energy structure and density of Cr₂AlC and Ti₂SnC.From the band structure diagram can be seen that the two substances are metal conductive material.This conclusion agrees with the reported experimental conclusion.Based on the calculation of the density of the states,the total density and the density of the two substances were analyzed,and the influence of the electrons on the total density was discussed.Combined with the electronic structure of Cr₂AlC and Ti₂SnC,the results by calculating the complex permittivity show that the peak of complex permittivity is mainly caused by the electron transition between 3d and 3p of Cr.The peak of complex permittivity of Ti₂SnC is mainly caused by the complex permittivity of 3d of Cr and 5s and 5p in Sn;the calculating results of photoconductivity of these two material,the photoconductivity of Cr₂AlC is mainly caused by the electron transition between 3d and3p of Cr.The peak of photoconductivity of Ti₂SnC is mainly caused by the electronic transition between 3d of Ti and 5s and 5p of Sn.Through the calculation of absorption coefficient,the refractive index and the loss function,it shows that absorption coefficients of the two compounds were in the high order of magnitude.The reason is the covalent effect of M-C,with a metallic which can absorb photons from electromagnetic wave to ultraviolet,without optical band gap;The refractive index extinction coefficient of being the peak mechanism is similar to the imaginary part of respective complex permittivity;Their loss function peaks correspond to the reflectance peaks and the reflectivity decreases rapidly when the loss function reaches the peak.The calculated reflectance of the two substances shows that the reflectance of Cr₂Al C and Ti₂SnC has almost no obvious change in the visible region,and the change of reflectance in the ultraviolet region is relatively large which can be seen that the two substances have good thermal stability.Combined with good electrical conductivity and self-lubricating properties,it is predicted that Cr₂AlC and Ti₂SnC can be used as a potential conductive composite material for the second phase additive and temperature control coating material.