Enhanced thermionic electron emission of (La1‐x‐yPrxBay)B6 cathode transforming from the grain boundary to the grain

Abstract The mixed rare earth/alkali earth was initially employed to enhance the thermionic emission performance of lanthanum hexaboride (LaB 6 ) through forming the high‐dense (La 1‐x‐y Pr x Ba y )B 6 polycrystal by spark plasma sintering (SPS). La 0.6 Pr 0.3 Ba 0.1 B 6 exhibits the highest current density in space charge limited (SCL) region at T = 1873K while La 0.5 Ba 0.5 B 6 has the highest current density in temperature limited (TL) region. The maximum current density of 14.07 A/cm 2 at T = 1673K for La 0.5 Ba 0.5 B 6 is higher than that of 11.71 A/cm 2 at T = 1873K for LaB 6 polycrystal, presenting superior emission characteristics at the low temperature, mainly ascribed to the contribution of the Ba element. With the increase in the Ba content, the location of the highest electron emission shifts from the grain boundary (in La 0.5 Pr 0.5 B 6 and La 0.6 Pr 0.3 Ba 0.1 B 6 ) to the internal grain (in La 0.6 Pr 0.1 Ba 0.3 B 6 and La 0.5 Ba 0.5 B 6 ). The consumption rate of the elements during thermionic emission follows the order: Ba > Pr > La. The experimental data on the current density aligns closely with the theoretical predictions, demonstrating the emission of (La 1‐x‐y Pr x Ba y )B 6 ceramic obeys classical thermionic emission mechanism of metals.