We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared… Click to show full abstract
We have tested the conduction band electrons of lanthanum hexaboride that is among the most effective electron-beam sources with one of the highest brightness of thermionic emission. We performed infrared spectroscopic, DC (direct current) resistivity and Hall-effect studies of LaB6 single crystals with various 10B and 11B isotope content. We find that only a small amount of conduction electrons behave as Drude-type charge carriers while about 70% of the electrons are involved in collective oscillations of electron density coupled to vibrations of both the Jahn-Teller unstable rigid boron cage and rattling modes of La-ions loosely bound to the lattice. We suggest that exactly these non-equilibrium conduction electrons determine the extraordinary low work function of thermoemission in LaB6.
               
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