Investigation on the Impact of Sr on Emission Property of Scandate Cathodes

Scandate cathodes have received widespread attention due to the high emission current density, existing results have shown that the content of strontium in impregnant has a certain degree of impact on the emission property of scandate cathodes. In this work, the mechanism by how strontium affects the emission property was investigated through experiments and theoretical analysis. Five precursor powders with different strontium element contents were prepared by freeze-drying method, and the impregnant was obtained after sintering. Then composition analysis was conducted on the impregnant and prepared experimental cathodes for emission performance testing, also the surface emission structure of cathode was established for density functional theory (DFT) calculations. The experimental results indicated that the variation in strontium content can alter the material composition of the impregnant and have impact on cathode emission performance. During the process of increasing strontium content from 0 to 12 atom%, the emission performance of the experimental cathodes increased first and then decreased. Under a testing temperature of 1100
$^{\circ }\text{C}_{\text {b}}$
, the cathodes with 6 atom% Sr have the highest emission current density of 34.9 A/cm2 at 260 V dc and 523.2 A/cm2 at 2000 V pulse voltage among the five experimental cathodes, and this cathode exhibits good emission uniformity. DFT results indicate that strontium does not directly participate in reducing the work function of cathode surface. It can be considered that strontium has a promoting effect on the formation of active substance, an appropriate amount of strontium promotes the formation of emitting active substance Ba2ScAl5 during the preparation process of the impregnant, thus promoting the improvement of cathode emission performance; while excessive strontium can lead to the generation of impurities that lower the emission performance of cathodes.