In situ(La_xGd_1−x)B₆cathode materials prepared by the spark plasma sintering technique

Polycrystalline hexaborides (LaxGd1−x)B6 (x=0, 0.6, 0.8, 1) were synthesized by the reactive spark plasma sintering (SPS) method using a mixed powder of LaH2, GdH2 and B. The effects of La doping contents on the crystal structure, grain orientation, electrical resistivity and thermionic emission properties were investigated by x-ray diffraction, electron backscattered diffraction and emission current measurements, respectively. The results indicate that the high-purity (LaxGd1−x)B6 cathode sintered by SPS exhibits high densification (>97%) and a high value of the Vickers hardness (2375 kg mm−2). When the La doping contents are increased, the thermionic emission current density increases from 11.00 to 36.20 A cm−2. Thus, the SPS technique is a suitable method for synthesizing dense rare-earth hexaborides with excellent properties.