Effect of Holding Temperature on Growth of Ruby Crystal Films via Molybdenum Trioxide Flux Evaporation–Solubility of Aluminum Oxide, Growth Rate, and Material Balance

Ruby (Al₂O₃:Cr) is used not only for jewelry but also in various industrial materials because of its excellent mechanical, optical, and chemical properties. Ruby crystals have been grown using the molybdenum trioxide (MoO₃) flux evaporation method. Herein, we report the effect of holding temperature on the growth of ruby crystal films via MoO₃ flux evaporation. All temperature effects were investigated considering the epitaxial growth of ruby crystal film on sapphire crystal substrates. First, the solubility curve of aluminum oxide (Al₂O₃) in MoO₃ flux was examined in the temperature range 1050–1200 °C. The difference in solubilities between 1050 and 1200 °C was ∼0.4 mol %. However, higher temperatures increased the crystal film growth rate due to increased flux evaporation rate. The difference in the crystal growth rate produced a difference in the surface pattern of the ruby crystal films. The surface of the ruby crystal films exhibited ellipsoidal patterns with a wide step interval at 1100 °C and circular patterns with a narrow step interval at 1200 °C. Finally, the material balance between the dissolved mass supplied by the dissolution of the substrates and the mass of grown ruby crystals was investigated. All dissolved solutes were found to be crystallized in ruby crystals, either in film or in particle form.