Thermionic Emission Capability of the Ba–Sc–Al–O Compound Synthesized by High-Temperature Solid-State Process

The dibarium scandium aluminum oxide (Ba2ScAlO5) is an important compound for thermionic emission in high-power vacuum devices. Herein, the high-temperature solid-state synthesis mechanism is investigated extensively to develop single-phase
$\beta $
-Ba2ScAlO5 and evaluate its emission capacity. Barium carbonate, scandium oxide, and aluminum hydroxide are adopted as the reactants. The synthesis temperature, the intermediate phases, and the cell parameters of the final products differ from sintering the coprecipitated precursor. The
$\beta $
-Ba2ScAlO5 single-phase material can be obtained based on the nonstoichiometric mole ratio of BaO:Sc2O3:Al2O3 = 4.4:1.1:0.9. The X-ray Rietveld refinement reveals that the substitution of Sc for Al and the defects of the Ba, Sc, and O vacancies account for the nonstoichiometry and the shrinkage of cells. The test cathode impregnated with
$\beta $
-Ba2ScAlO5 doped with Ca2+ exhibits an emission capability of 6.79 A/cm2 at 900
$^{\circ }\text{C}_{\text {B}}$
in the dc mode. This work demonstrates the feasibility of obtaining
$\beta $
-Ba2ScAlO5 with considerable emission through the high-temperature solid-state process.