Abundance of oxygen radicals residing in the cage-like lattice framework of calcium aluminate makes the growth of good quality single crystal difficult. Oxygen bubbles easily get trapped inside the crystal making the optical properties of the crystal inferior. In this study, we have investigated the behavior of oxygen bubbles inside the molten-zone during a conventional floating-zone growth. We have investigated the effect of different feed preparation process on the quality of the grown crystals and found that subsequent quenching of the feed from 900 °C after calcination at 1200 °C significantly reduces the bubbles in the crystal. Secondly we have performed floating-zone growth of C12A7 under a high magnetic field (up to 8T). We think that each of the bubbles become a small piece of magnet under the magnetic effect and repel each other in the molten zone. As a result we observed significant stabilization of the molten zone through early removal, and a reduction of accumulation of the bubbles.

Keywords: Calcium aluminate, Superconducting magnet, Magnetic field, Floating zone technique