Pore-free 12CaO•7Al2O3 single-crystal growth by melt state control using the floating zone method

Pore-free < 110 > oriented 12CaO center dot 7Al(2)O(3) (C12A7) single crystals with sizes up to 7 mm (Phi) x 40 mm are grown by controlling the melt states in a floating zone (Fz) method. Control is achieved by increasing the melt temperature to similar to 1495 degrees C and using a high-density C12A7 polycrystalline feed rod, which reduces oxygen bubbles in the melt almost completely due to a distinct decrease in O-2-solubility with temperature increase. The optimization of the melt temperature, coupled with < 110 > oriented single crystal as a seed and the decreased growth speed, allows high-quality crystal growth. The grown crystal exhibits a good internal transparency (above 98% in the visible region) and does not contain magnetic impurities such as Ir, which are inevitably incorporated in Czochralski grown crystals. The crystal can be used as a precursor for superconductive C12A7:e(-).