Growth of 12CaO·7Al₂O₃ single crystal with tetragonal symmetry by Czochralski method

Single crystals of 12CaO·7Al₂O₃ (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 Ir⁴⁺ ions of ∼ 5 × 10¹⁷ cm^{- 3}, presumably occupying at Ca²⁺ sites. High resolution X-ray diffraction analyses indicated that the C12A7 single crystal shows the tetragonal symmetry belonging to the space group I over(4, -) 2 m.