Special features of thermionic emission properties of single crystals of GdB4 and GdB6

Single crystal growth of GdB6 by the optical floating-zone technique

“…J 0 is calculated to be 0.92 A cm −2 at 1673 K, 1.32 A cm −2 at 1773 K, and 1.52 A cm −2 at 1873 K, respectively, and the corresponding work functions of GdB 6 are 2.84 eV at 1673 K, 2.98 eV at 1773 K, and 3.14 eV at 1873 K, respectively. The average work function of GdB 6 is 2.99 eV, which is much lower than those from previous research studies, [14][15][16][17] indicating that the pure GdB 6 single crystals grown by the improved process have higher emission properties.…”

“…The work function of GdB 6 single crystals with a large size is reported to widely range from 3.1 eV to 3.8 eV (ref. [14][15][16][17] while the work function of singlecrystalline GdB 6 nanowires is only 1.5 eV, 11 which is considered to have the lowest work function among the rare earth hexaboride family. Therefore, further investigations of its thermionic emission properties including the work function are needed.…”

“…Even if a GdB 6 single crystal is cut from the as-grown crystal, the impurities have already damaged the quality of the crystal. 15 Another way to avoid the formation of GdB 4 impurities is the addition of excess boron into a polycrystalline rod, which can effectively avoid GdB 4 impurities, but excess boron can also weaken the thermionic emission properties of the GdB 6 single crystal, with the work function of which being as high as 4.2 eV. 17 Therefore, the preparation of high-purity GdB 6 single crystals without GdB 4 impurity becomes worthy and necessary.…”