Preparation and Emission Performance Investigation of Yttrium-Doped Impregnated Scandate Cathode

Abstract

The application of scandate cathode with high emission current density in microwave vacuum electronic devices is constrained by issues of poor emission uniformity and reproducibility. An effective strategy to enhance the emission performance of scandate cathodes is through the doping of additional elements. This article prepared yttrium-doped scandate cathodes and investigated the mechanism of yttrium affecting cathode emission performance via impregnant composition analysis, cathode emission property testing, surface element analysis, and density functional theory (DFT) calculations of surface work function and adsorption energy. As the yttrium content increases from 0 to 6 atom%, the total amount of aluminate compounds remains above 85%. The content of Ba2ScAlO5 in impregnant increased first and then decreased, while cathode emission property test results also increased first and then declined. The cathode with yttrium content of 3 atom% in impregnant has the best emission property, with an emission current density of 466.4 A/cm2 at 2000 V pulse voltage under 1100 ° Cb, the practical work function of 1.64–1.68 eV. The theoretical surface work function of the ${x} = 3$ cathode is 1.67 eV, and the theoretical adsorption energy indicates a low evaporation rate on the surface of yttrium atoms during cathode operation. It can be inferred that the doping of yttrium has a visible impact on the composition of the impregnant. An appropriate amount of yttrium doping facilitates the formation of Ba2 ScAlO5 and enhances cathode emission properties, while superfluous yttrium inhibits Ba2ScAlO5 formation and results in an increased presence of BaY2O4 in impregnant, reducing the coverage of Ba atoms on the cathode surface, suppressing the enhancement of cathode emission performance.