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

摘要

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.