Spark plasma sintered Ce/Gd co‐doped lanthanum hexaboride with enhanced thermionic emission properties

Abstract This study investigates the effect of Ce/Gd co‐doping on the work function and thermionic emission properties of lanthanum hexaboride (LaB 6 ). Density functional theory calculations demonstrate that the Ce/Gd co‐doping effectively reduces the work function of LaB 6 , with the value decreasing from 2.11 eV for the LaB 6 (100) surface to 2.09 eV for the La 0.5 Ce 0.25 Gd 0.25 B 6 (100) surface. Using spark plasma sintering, Ce/Gd co‐doped LaB 6 bulks with a CsCl‐type single‐phase substitutional solid solution structure were fabricated, achieving relative densities exceeding 96.2%. The dense SPSed specimens exhibit no noticeable texture, comparable average grain size, and a homogeneous distribution of rare‐earth metal cations. The H v value of 21.2 ± 0.54 GPa for La 0.5 Ce 0.25 Gd 0.25 B 6 is higher than that of 18.5 ± 0.60 GPa for LaB 6 , which can be ascribed to the solid solution strengthening effect induced by Ce/Gd co‐doping; however, the Ce/Gd co‐doping is incapable of improving fracture toughness. Ultraviolet photoelectron spectroscopy analysis further confirms that the work function of Ce/Gd co‐doped LaB 6 (2.58 eV for La 0.5 Ce 0.25 Gd 0.25 B 6 ) is lower than that of pure LaB 6 (2.68 eV). Importantly, under identical operating conditions, the dense La 0.5 Ce 0.25 Gd 0.25 B 6 bulk demonstrates higher thermionic emission current densities than LaB 6 , highlighting its promising potential as a high‐performance thermionic cathode material.