Abstract: An improved process for growing single crystals of ceramic material according to the gradient furnace technique is disclosed. The process combines the gradient furnace technique with principles of zone leveling and comprises seeding the melt of a ceramic material in a crucible, heating the crucible to above the melting point of the material and solidifying the material to form a single crystal by extracting heat from the bottom portion of the crucible. The application of zone leveling principles to this system comprises melting the ceramic material by creating a molten zone at the bottom portion of the crucible and passing the zone up the crucible to progressively melt successive portions of the ceramic material therein.

Abstract: A method for the production of improved, transparent single crystals having a corundum structure under conditions of minimum thermal strain, comprising the optimum orientation of growth planes of a seed crystal in a melt substantially parallel to the vertical side wall means of a crucible, and heating and subsequent cooling the melt, thereby nucleating on the seed crystal.