Experimental and first-principles investigations on W-Ir mixed matrices cathodes with improved emission performance

Abstract

Fundamental understanding of the intrinsic emission mechanism of mixed W matrix Ba type dispenser cathode is critical to rational design of advanced device with highly desired performance. In this work, experimental and theoretical work was conducted to investigate the underlying effect of Ir metal on the improved emission properties of mixed W cathodes. The results indicated that introduced Ir improves the stability of Ba-O dipole on the cathode surface by alloying with W rather than reaction with impregnants, which leads to higher atomic ratio of Ba/O on the surface emission layer with 50 wt% Ir adding, and therefore accounts for the enhanced emission current density of 11.90 A/cm2 with 2.2 times higher than W matrix dispenser cathode at 1000 ℃b. Furthermore, first-principles calculation was used to investigate the adsorption energy, work function, Bader charges, dipole moment and d-band center based on the high stable configuration of Ba0.25O0.5 adsorbing on IrW (111) and W (110), which explains the lowed work function of Ir-W cathode and in turn improved the emission property.