Preparation And Physical Properties Of Nanocrystalline Ce_xBa_1-xB₆

In this paper,first studied the preparation and physical properties of Ce_xBa_1-xB₆.Rare earth oxide CeO₂,alkaline oxide Ba O and NaBH₄ as raw materials were used to prepare the multiple rare earth hexaboride Ce_xBa_1-xB₆.When the reaction temperature was 1150°C,the Ce doping effects which content is x=0.1?0.3?0.5 and 0.7 on phase composition,morphology and microstructure were studied.The XRD results showed that all the synthesized powders have a CsCl type single phase with space group of Pm-3m.The SEM results showed that there were exists some cubic-shape micro-crystalline for Ce_0.3Ba_0.7B₆ and the average grain size of CeB₆ was 100 nm.The EDS results of TEM for Ce_0.5Ba_0.5B₆ single crystal confirmed the Ce atoms randomly occupied the lattice site of Ba atom.As a result of light absorption measurement,it was found blue shift phenomenon that the absorption peak and absorption valley of Ce_0.3Ba_0.7B₆ slightly shifted from 300 nm in the ultraviolet region to 600 nm in the visible region.Secondly,the electronic structure and optical properties of barium hexaboride?Ba B₆?were studied by"first principles".It is concluded that the valence band top of the alkaline earth hexaboride?BaB₆?and the bottom of the conduction band are located at the same point of symmetry of the Brillouin zone.This result proves that BaB₆ is a direct band gap semiconductor.The state density analysis shows that the valence band of BaB₆ is mainly determined by the B-2p state,and the bottom of the conduction band is determined by both the Ba-3d state and the B-2p state.The calculated static permittivity?1?0?of BaB₆ is 9.647.The peak of the imaginary part of the dielectric function is related to the transition of electrons in the band.The result of the reflection spectrum is similar to the result of the absorption spectrum,and the spectrum lines all have a steep descent at the energy of 25e V.The energy loss spectra of alkaline earth hexaboride BaB₆ were analyzed,the characteristic peak appeared at an energy of 25eV,and the peak of the loss spectrum corresponded to a sharp drop in the absorption and reflection spectra.Finally,the single crystal CeB₆ emission performance and magnetic anisotropy were studied.The?110???111???210?and?310?planes of monocrystalline CeB₆ were oriented by X-ray Laue method.The effects of different crystal plane thermal emission properties and magnetic field on the resistivity were studied systematically.The results show that the maximum emission current densities of?110???111???210?and?310?are 38.4?11.54?50.4 and 20.8 A/cm² at the cathode temperature of 1873K,It shows the"anisotropy"of the emission performance.The Richardson-Dushman formula to calculate the work function shows that the?210?crystal face has the lowest work function of 2.4 eV.From the practical point of view,the crystal face is expected to replace the commercial tungsten filament to become a new generation of field emission cathode material.The measurement results of magnetoresistance show that the resistivity changes from 73??·cm to 69??·cm when the crystal rotates from[001]to[011]direction,it shows that resistivity also has"anisotropy"in different directions in the magnetic field.