Electronic structures and emission properties of typical binary single crystal REB₆

Abstract

Binary rare earth hexaborides (REB₆) have different rare earth elements with different valence electron distributions, which lead to different strange physical properties and different emission properties. However, in the electron emission properties, whether PrB₆, NdB₆, SmB₆ and GdB₆ all have excellent emission properties remains to be further studied, and the physical mechanism affecting their emission properties needs investigating. In this paper, the electronic structures, work functions of typical binary single crystal REB₆ (LaB₆, CeB₆, PrB₆, NdB₆, SmB₆, GdB₆) are studied by first principles calculations. The single crystal REB₆ are prepared by optical zone melting method, and their thermionic electron emission properties are tested experimentally. The theoretical calculation results show that the typical binary REB₆ have large densities of states near the Fermi level. The d-orbitals with broad distributions in conduction bands are beneficial to electron emission. The localized f-orbital electrons in valence bands are not conducive to their electron emission. The theoretical calculations of work functions of typical binary single crystal REB₆ (100) surface are consistent with the analyses of their electronic structures. The theoretical calculation values of work functions are ordered as GdB₆ (2.27 eV) < CeB₆ (2.36 eV) < LaB₆ (2.40 eV) < PrB₆ (2.58 eV) < SmB₆ (2.63 eV) < NdB₆ (2.91 eV). The experimental test results of thermionic electron emission of single crystal show that the experimental thermionic electron properties are consistent with the theoretical ones. The LaB₆ and CeB₆ both have good thermionic and field emission properties, and the GdB₆ has excellent field emission properties.