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

A high-quality and large-sized GdB6 single crystal was successfully prepared by using the optical floating zone method to accurately control the temperature and composition of the molten zone. A GdB6 [100] single crystal 25 mm in length and 5 mm in diameter was obtained. The full width at half-maximum (FWHM) of the X-ray rocking curves was 0.227°, which indicated that the as-grown GdB6 single crystal had a high quality. The maximum thermionic emission current density of the GdB6 single crystal was 6.73 A cm−2 at U = 4000 V and T = 1873 K, and the average work function was 2.99 eV. Combining first-principles calculations and experiments, the work function was found to monotonically increase as the size of the GdB6 single crystal changed from nanostructure (1D) to bulk (3D).