Multicomponent hexaborides with low work functions by ultra-fast high temperature sintering

Abstract

A reduction of the work function (Wf) in multicomponent hexaborides has been achieved by doping with highly electropositive Ba, which enhances electron emission. Single-phase bulk multicomponent polycrystalline hexaborides of La0.5Ba0.5B6, Ce0.5Ba0.5B6, and BaB6 powders were first synthesized and then densified by ultra-fast high temperature sintering. Using a total reaction and densification time of 6 min, a density of ∼90% theoretical was reached. The UHS sintering is a resistive heating technique, which enables a high heating rate (∼103–104 °C/min) to reach the synthesis/sintering temperature in a minute and facilitates in synthesizing single phase solid solution product very quickly (in 6 min). Measurements of Wf were carried out by Kelvin Probe Force Microscopy, yielding values of Wf = 2.05 ± 0.10 and 2.00 ± 0.10 for La0.5Ba0.5B6 and Ce0.5Ba0.5B6 respectively. These values of Wf are similar to those predicted by first-principles calculations. Ba-substitution is shown to be a general approach to reduce Wf (∼25%) in various multicomponent hexaborides.