The effect of precursor boron nanopowder on the microstructure and emission properties of LaB6cathode materials

Two different structured boron sources have been used for the fabrication of LaB6 ceramics and their effects on the sintering temperature, microstructure and emission properties were investigated. The results show that the reaction temperature of amorphous boron and La to form LaB6 is 1200 C, which is 150 C lower than the reaction using crystalline boron. The grain size of LaB6 prepared by amorphous boron and La is 150 nm, which is much smaller than that of crystalline boron ∝2 μm at the same sintering condition. With the grain size decreasing from 5 μm to 150 nm, the LaB6 thermionic emission current density increases significantly and the field emission turn-on field decreases from 1500 V to 1300 V. Using amorphous boron nanopowder can not only enhance the microstructure but also improve the emission properties. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)