Single-phase (Ba,Ca)2ScAlO5 impregnant for dispenser cathodes with enhanced thermionic emission performance

(Ba,Ca)2ScAlO5 compounds are synthesized and improved emission performance is achieved by virtue of their single-phase structure and low work function. The substitution of Ca2+ for Ba2+ effectively lowers the melting points of (Ba,Ca)2ScAlO5 from over 1800 °C–1700 °C when the Ca2+ substitution reaches 20 at%. During sintering, the co-precipitation precursor first reacts to form (Ba,Ca)3Al2O6 near 912 °C before reacting with BaCO3 and Sc2O3 at the higher temperature of 1186 °C to generate (Ba,Ca)2ScAlO5. Emission tests reveal that the maximum full space charge current density is 9.6 A cm−2 at 1000 °CB (brightness temperature) for the cathode impregnated with single-phase (Ba,Ca)2ScAlO5. Low work function (~1.5 eV) and good emission uniformity make such a cathode promising for applications in high-power microwave devices.