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

Abstract

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.

Form Design of Bulky Ruby Crystals with Well-Developed (112̅3) Faces—Epitaxial Growth of Crystal Films on Sapphire Substrates via MoO3 Flux

“…We focused on the MoO 3 flux because it is easy to handle. Thus far, we have conducted research to understand various conditions, i.e., solubility, 14,15 holding temperature, 15 and flux evaporation control, 16 for growing ruby crystals.…”

“…If ruby single crystals with few defects can be easily grown, they can be used as jewelry and industrial materials. Numerous studies on the artificial growth of ruby crystals were performed using various techniques, such as Verneuil, , Czochralski, hydrothermal, vapor-phase, and flux methods. − In particular, the flux methodclassified as solution growthis expected to grow high-quality ruby crystals because the generation of defects can be inhibited by the crystal growth that is close to equilibrium.…”

“…The ruby crystals were grown from lead fluoride–boron trioxide (PbF 2 -B 2 O 3 ) and cryolite (Na 3 AlF 6 ) flux. − However, the separation of flux from the ruby crystals was difficult. Evaporation of molybdenum trioxide (MoO 3 ) flux is useful for the growth of ruby crystals. − The flux was completely evaporated and easily separated from the ruby crystals. We focused on the MoO 3 flux because it is easy to handle.…”

“…We focused on the MoO 3 flux because it is easy to handle. Thus far, we have conducted research to understand various conditions, i.e., solubility, , holding temperature, and flux evaporation control, for growing ruby crystals. Further, it is necessary to understand the relative difference in the growth rate of the ruby crystal grown from MoO 3 to control the form of the crystal.…”

“…Based on the relative differences in the growth rate of ruby crystal and the dissolution rate of sapphire crystal for each crystal face, the shape of the sapphire seed crystal was determined. Furthermore, growth temperature, solute mass, and control condition of flux evaporation for growth of a bulky ruby crystal were determined by the knowledge of an effect of temperature on ruby crystal growth, a solubility of Al 2 O 3 to MoO 3 , , and a role of evaporation inhibitor, respectively.…”