High-quality ZrB2 single crystals with diameters of 13 mm and lengths of 45 mm were grown from boron-rich molten zones (boron 80 mol%), using the RF heated floating-zone method. The (0 0 0 1) single crystals were also grown using seed crystals. Control of temperature gradients on the growing interfaces was performed by arranging ceramic cylinders around the growing crystals and the feed rods. This made it possible to grow high-quality ZrB2 single crystals free of defects such as lineage structures observed in X-ray topographies of cross-sections. In the central areas (3 mm square) of the grown crystals, the full-widths at half-maximum (FWHM) of the X-ray rocking curve ((10 - (1) over bar0) diffraction) were improved to 24.5-42.4 arc see compared with the crystals obtained until now. The ZrB2 obtained seems to be quite suitable for substrates of GaN. (C) 2007 Elsevier B.V. All rights reserved.