Enhanced thermionic emission properties in textured two-phase LaB6–BaB6 system prepared by spark plasma sintering

Abstract

Structure, crystallographic orientation, and thermionic emission properties of the two-phase LaB6–BaB6 system fabricated by a combined process of evaporation–condensation and spark plasma sintering (SPS) were investigated systematically. The powder X-ray diffraction (XRD) reveals that the obtained nominal composition (La0.6Ba0.4)B6 compound exhibits coexistence of two isostructural phases of LaB6 and BaB6. The electron backscatter diffraction (EBSD) confirms that the surface of the (La0.6Ba0.4)B6 forms a clear (001) texture, which favors reduction in work function. Thermionic emission properties were measured in the temperature range between 1500 and 1873K. The results indicated that the (La0.6Ba0.4)B6 emitter displayed a low work function of 1.95eV, and a high zero field emission current density of 10Acm−2 at 1773K. Compared to the reported LaB6 and (La0.6Sm0.4)B6 prepared for identical synthesis conditions, (La0.6Ba0.4)B6 is shown to have the most excellent thermionic emission performance and could be promising candidate for cathode material applications. It was revealed that the addition of BaB6 to LaB6 plays an important role for the reduction of work function and enhancement of electron emission properties.