Growth of Hexagonal Bipyramidal Ruby Crystals by the Evaporation of a Li2O–MoO3 Flux

Abstract The growth of hexagonal bipyramidal ruby crystals by the flux evaporation method in the Li2O–MoO3 flux system has been reported. Ruby crystals were grown by heating a mixture of a solute (Al2O3 + 0.5 wt % Cr2O3) and a flux (Li2O–MoO3) at 1050, 1100, or 1200 °C, followed by holding the solution at these temperatures for 5 h. The crystal size was dependent on the evaporation loss of the flux. The evaporation loss of the flux gradually decreased with increasing amount of Li2O added to MoO3, and increased with the holding temperature. The obtained ruby crystals had lengths of up to 2.6 mm and widths of up to 2.1 mm, and had a transparent-red color. Their form was a bipyramid, bounded by well-developed faces. The most suitable flux composition for high-quality and large ruby crystal growth was found to be 2 mol % Li2O–98 mol % MoO3.