First Priniciples Study Of The Physical Properties Of Rare Earth Tetraborides

Rare-earth metal borides have become one of the research hotspots due to the combination of electron-deficient boron clusters and rare-earth atoms,and the relatively localization of rare-earth atoms beneficial to stabilize the outer electrons forming various structures,which attracted considerable interest in thermal electron emission,chemical stability,hardness,high melting point,low-power function,narrow-band semiconductors.Previous studies have shown unusual magnetism of rare earth tetraborides,while few studies have focused on the effect of electronic structures on magnetism.In this dissertation,the magnetic and electronic structures of the rare earth tetraboride Nd B₄are discussed using the first-principles method based on density function theory,and the magnetic ground state and optical properties are predicted.The main content is as follows:1.All of the fourteen possible magnetic structures have been predicted.The results show that the magnetic ground state of Nd B₄tends to G-type antiferromagnet,and the energy of the magnetic structure differs slightly from the magnetic ground state,which is easy to change with the external conditions.Near the Fermi level,the electron states are dominated by Nd-f orbital electrons,and there is a strong hybridization between Nd-d orbits and B-p orbital electrons.2.The electron emission and optical properties of rare earth tetraborides are discussed.The calculation results for the work functions of six tetraborides,La B₄,Ce B₄,Dy B₄,Nd B₄,Er B₄,Gd B₄,on the main crystal planes（001）,（100）and（110）and on different end surfaces show that the work functions of different surface configurations are different and anisotropic.The crystal plane with the lowest work function is determined to be（100）,with the lowest value of La B₄work function.The results of optical properties show that tetraborides have excellent light absorption properties in the ultraviolet-visible region,and Nd B₄has the highest reflectivity in the short-wave infrared region,which can be used as potential radiation shielding materials or spectral selective materials.3.The properties of doped rare earth tetraborides are discussed.Three materials with the lowest work function were selected for doping at different ratios.Nine compounds of La_0.5Ce_0.5B₄,La_0.5Nd_0.5B₄,La_0.25Ce_0.75B₄,La_0.25Nd_0.75B₄,La_0.75Ce_0.25B₄,La_0.75Nd_0.25B₄,Nd_0.5Ce_0.5B₄,Nd_0.25Ce_0.75B₄,Nd_0.75Ce_0.25B₄were calculated.The results show that Nd doped Ce B₄has lower work function,higher absorption coefficient and reflectivity in the ultraviolet region,which can effectively shield ultraviolet light,and then decrease sharply,and lower absorption coefficient and reflectivity in the visible region.Compared with binary tetraboride,the absorption coefficient in the ultraviolet region increases slightly,and the reflectance in the infrared region increases significantly,indicating that it can be used as a spectral selective material and other related applications.