Single crystals of 12CaO center dot 7Al(2)O(3) (C12A7) have been grown by the Czochralski method with three different growth directions of (100), (110), and (111). Employment of a 2.0% oxygen-containing nitrogen atmosphere and use of an iridium crucible were the critical factors for obtaining the single crystal. The crystal exhibited orange color resulting from the incorporation of Ir(4+) ions of similar to 5 x 10(17) cm(-3), presumably occupying at Ca(2+) sites. High resolution X-ray diffraction analyses indicated that the C12A7 single crystal shows the tetragonal symmetry belonging to the space group I(-)42m. (C) 2007 Elsevier B.V. All rights reserved.