Growth stoichiometric magnesium aluminate spinel crystals by flux evaporation

Abstract

Crystals of MgAl 2O 4 over 1 cm in size have been grown both undoped and doped with first period transition elements by evaporating solutions of the constituents in molten lead fluoride. The crystal products are characterised by high crystalline perfection and, unlike spinel grown by other techniques, are stoichiometric. Details of the growth conditions and observations on evaporation rates both with and without the addition of boric oxide to the melt are given. At temperatures below 1150 °C, MgF 2 and α-Al 2O 3 are precipitated, which precludes the use of slow cooling techniques for growth. The crystal products are bounded solely by (111) faces, which occasionally show shallow growth pyramids indicative of spiral dislocations. Etching with hot phosphoric acid indicates that edge dislocation concentrations are less than 10 2 cm -2. Crystals of ZnAl 2O 4-MgAl 2O 4 and MgGa 2O 4-MgAl 2O 4 solid solutions have also been prepared.