Low temperature synthesis of low thermionic work function (LaₓBa₁₋ₓ)B₆

This study presents investigations of the microstructure, morphology and emission properties of the promising thermionic material (LaₓBa₁₋ₓ)B₆. The material was synthesised by solid-state reaction without post-synthesis purifications. Powder X-ray diffraction revealed that samples prepared at a temperature ≥1500 °C had formed a significant proportion of solid solution (above 54 mass%). Subsequent sintering at 1950 °C caused the formation of a mixture of three solid solutions with the dominant phase being (La_0.31Ba_0.69)B₆ ~85% (by mass). The Richardson work function and emission constant for this boride mixture were found to be 1.03 eV and 8.44 x 10^-6 A cm K^-2 respectively