Effect of Ba-doping on the Structural,Grain Orientation and Thermionic Emission Properties of Hexaboride GdB_6

The polycrystalline rare-earth hexaborides(BaxGd1-x)B6(x = 0,0.2,0.4,0.8) were prepared by the reactive spark plasma sintering(SPS) method using mixed powder of BaH2,GdH2 and B.The effects of Ba doping content on the crystal structure,the grain orientation and the thermionic emission properties of the GdB6 were investigated by X-ray diffraction,electron backscattered diffraction and emission current measurements.It is found that all the sintered samples exhibit high densification( 97%) and high value of Vickers hardness(2070 kg/mm2).The maximum thermionic emission current density of GdB6 is 11 A/cm2 at a cathode temperature of 1873 K,which is much higher than that of traditional method.With the increase of Ba content,the thermionic emission current density decreases from 11 A/cm2 to 2.25 A/cm2 at 1873 K.