The effect of samarium doping on structure and enhanced thermionic emission properties of lanthanum hexaboride fabricated by spark plasma sintering

Single‐phase polycrystalline solid solutions (La 1− x Sm x )B 6 ( x  = 0, 0.2, 0.4, 0.8, 1) are fabricated by spark plasma sintering (SPS). This study demonstrates a systematic investigation of structure–property relationships in Sm‐doped LaB 6 ternary rare‐earth hexaborides. The microstructure, crystallographic orientation, electrical resistivity, and thermionic emission performance of these compounds are investigated. Analysis of the results indicates that samarium (Sm) doping has a noticeable effect on the structure and performance of lanthanum hexaboride (LaB 6 ). The analytical investigation of the electron backscatter diffraction confirms that (La 0.6 Sm 0.4 )B 6 exhibits a clear (001) texture that results in a low work function. Work functions are determined by pulsed thermionic diode measurements at 1500–1873 K. The (La 0.6 Sm 0.4 )B 6 possesses improved thermionic emission properties compared to LaB 6 . The current density of (La 0.6 Sm 0.4 )B 6 is 42.4 A cm −2 at 1873 K, which is 17.5% larger than that of LaB 6 . The values of Φ R for (La 0.6 Sm 0.4 )B 6 and LaB 6 are 1.98 ± 0.03 and 1.67 ± 0.03 eV, respectively. Furthermore, the Sm substitution of lanthanum (La) effectively increases the electrical resistivity. These results reveal that Sm doping lead to significantly enhanced thermionic emission properties of LaB 6 . The compound (La 0.6 Sm 0.4 )B 6 appears most promising as a future emitter material.