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)B6 (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)B6 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 (La0.6Sm0.4)B6 possesses improved thermionic emission properties compared to LaB6. The current density of (La0.6Sm0.4)B6 is 42.4 A cm-2 at 1873 K, which is 17.5% larger than that of LaB6. The values of ΦR for (La0.6Sm0.4)B6 and LaB6 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 LaB6. The compound (La0.6Sm0.4)B6 appears most promising as a future emitter material. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)