an ampoule assembly for the growth of single crystal materials is particularly adapted for a micro - gravity environment and includes a plurality of centering rods for spacing a crystalline material from the inner surface of an ampoule . the centering rods are spaced relative to one another to form a dopant vapor passageway to provide uniform stoichiometry of the crystal upon melting and resolidification . minimum contact between ampoule and the crystalline material ensures greater purity of the crystalline material when the material is transformed into a single crystal .