Study On Preparation And Properties Of CeB₆ Crystal

Rare earth hexaboride（RB₆）is a thermoelectric emission cathode for industrial applications due to the advantages of high melting point,low work function,high resistance to bombardment ability.CeB₆ is a kind of cathode material with good application prospect owning lower work function,stronger ability to resist carbon pollution,lower evaporation rate and higher resistivity compared with LaB₆ cathode.However,there are relatively few investgations on the CeB₆ cathode so far,thus it’s necessary to systematically study the preparation and performance of the material.Based on this situation,the high quality CeB₆ crystal was prepared by spark plasma sintering（SPS）combining optical zone melting in this paper.The influence of process parameters on the mechanical properties and electrical properties was investigated systematically.The CeB₆ polycrystalline bulk was prepared by SPS and the effect of sintering temperature and pressure on the mechanical properties of CeB₆ was studied.The density,Vickers hardness and bend strength of CeB₆ bulk increases with the elevated temperature under the constant pressure.The mechanical properties also have the same variation tendency with the increased pressure.The optimised process parameters are T=1900oC,P=50 MPa,t=5 min,under which CeB₆ specimen with density of 95.88%,hardness with 19.37 GPa and bend strength with 124.82 MPa is obtained.As the test temperature augments,the resistivity of the CeB₆ bulk is gradually increasing.The thermoelectric emission result shows that the maximum emission current density is 18.45 A·cm^-2 at 1700℃ and the minimum effective work function of 3.05 eV is obtained.The high-quality and full-density Ce B₆ single crystal was prepared by optical zone melting technique.The structure and quality of single crystal were characterized by single crystal X-ray diffraction,Raman spectroscopy and rocking curve.The single crystal possesses excellent mechanical properties,the Vickers hardness of 20.16 GPa and bend strength of 567.87 MPa,which have a significant improvement compared with polycrystalline CeB₆.Study on thermoelectric emission characteristics of different crystal planes shows that（100）crystal plane has the superior emission performance and the emission current density reaches to 25.04 A·cm^-2 with the applied voltage up to 1 KV and temperture of 1600℃.