Epitaxial Growth of Ruby Crystal Films on Sapphire Crystal Substrates and Solubility of Aluminum Oxide in Molybdenum Trioxide Flux

Abstract

Ruby (Al2O3:Cr) crystal films were, for the first time, epitaxially grown on sapphire (Al2O3) crystal substrates via the evaporation of molybdenum trioxide (MoO3) flux. The crystal films were grown by heating the flux placed on the sapphire crystal substrates at 1100 °C for 1200 min. The films thus obtained exhibited a red color and were approximately 200 μm in thickness. Based on the X-ray diffraction and electron backscatter diffraction analyses data, the crystallographic orientation of the crystal films was found to be the same as that of the substrate crystals. A ruby crystal film with a (0001) face developed on the (0001) substrate face, and a film with a (112̅0) face developed on the (112̅0) substrate face. In addition, the solubility of Al2O3 in the flux at 1100 °C was estimated to be approximately 9.6 mol % by measuring the mass loss of the substrate and the amount of evaporated flux when the crystallization of the ruby crystals occurred.

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.…”

“…Thus far, ruby crystal films have been epitaxially grown on sapphire crystal substrates with well-developed c(0001) and a(1120) faces via MoO 3 flux evaporation. 14 Through epitaxial growth of ruby crystal films on substrates, it is possible to determine the relative difference in growth rate for each crystal face. If the relative difference in growth rate for each crystal face during crystal growth from the selected flux is known, a crystal with the desired form can be designed.…”

“…Al 2 O 3 was added to the MoO 3 flux at a concentration of 6 mol %, to prevent the seed crystal from dissolving too much and growing a large ruby crystal. In our previous studies, the solubility of Al 2 O 3 to MoO 3 at 1100 °C was calculated to be 9.6 mol %, 14 which did not match the prepared solute concentration. As powder Al 2 O 3 and some of the seed crystal also dissolved in the flux, ruby crystals began to grow via the equilibrium point.…”

“…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.…”