Growth of TiO$_2$(rutile) single crystals by FZ method under high oxygen pressure

High oxygen pressure has been applied for a floating zone (FZ) crystal grower in order to grow high quality (rutile) single crystals suitable for optical application. The crystals, grown under 0.3, 0.4, 0.5, and 0.8MPa oxygen pressure respectively, are all transparent and dark blue. The degree of the presence of sub-grain boundary in the crystal differs from the applied oxygen pressure. In particular, single crystals grown under0.5 MPa showed sub-grain boundary-free and estimated good for optical devices.