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

• (La0.6Ba0.4)B6 has been successfully prepared by spark plasma sintering.
• The obtained (La0.6Ba0.4)B6 compound is a two-phase mixture of LaB6 and BaB6.
• The (0 0 1) texture is favorable for the decrease of work function.
• The addition of BaB6 to LaB6 improves the electron emission performance.
• (La0.6Ba0.4)B6 is shown to be promising candidate for cathode applications.

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 (0 0 1) texture, which favors reduction in work function. Thermionic emission properties were measured in the temperature range between 1500 and 1873 K. The results indicated that the (La0.6Ba0.4)B6 emitter displayed a low work function of 1.95 eV, and a high zero field emission current density of 10 A cm−2 at 1773 K. 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.

Room temperature XRD patterns of the nominal composition (La0.6Ba0.4)B6 synthesized by SPS at 1400 °C for 5 min under 50 MPa. The XRD patterns reveal that the (La0.6Ba0.4)B6 is a two-phase mixture of LaB6 and BaB6. The inset is a macroscopic picture of the obtained (La0.6Ba0.4)B6.Figure optionsDownload as PowerPoint slide