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 (La1-xSmx)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 LaB6 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 (LaB6). The analytical investigation of the electron backscatter diffraction confirms that (La0.6Sm0.4)B-6 exhibits a clear (001) texture that results in a low work function. Work functions are determined by pulsed thermionic diode measurements at 1500-1873K. The (La0.6Sm0.4)B-6 possesses improved thermionic emission properties compared to LaB6. The current density of (La0.6Sm0.4)B-6 is 42.4Acm(-2) at 1873K, which is 17.5% larger than that of LaB6. The values of phi(R) for (La0.6Sm0.4)B-6 and LaB6 are 1.98 +/- 0.03 and 1.67 +/- 0.03eV, 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 LaB6. The compound (La0.6Sm0.4)B-6 appears most promising as a future emitter material.