Diffusion coefficients of sapphire and ruby crystals

Diffusion coefficients of sapphire and ruby crystals

The diffusion coefficients of Cr3+ and Fe3+ in sapphire and ruby are temperature-dependent (Table 2.12) [82]. The diffusion coefficient of oxygen in sapphire is 4.2•10-20 cm2s-1 at 1,473 K [83]. That is, oxygen The diffusion path does not exceed 2.5 Å/h. In the temperature range from 1,853 to 2,113 K, the diffusion coefficient of 16O is 1.56•10-10m2s-1[84], and the activation energy is equal to 788±29 kJ/mol.

The relationship between diffusion and crystallographic direction has not been fully studied. Reference [85] reported that the diffusion of 22Na along the C-axis is twice as high as that along the direction perpendicular to the C-axis.

Evolution of ion-implanted sapphire surface and surface-adjacent layers under heat treatment. Metal and gas ions, including those that are impossible or difficult to implant into the surface-adjacent layer during growth, can be introduced by ion bombardment. Mn, Ni, Ce, Xe plasmas are implanted at temperatures from -170 to 250K. The metering varies from 3•1016 to 5•1017 cells/cm2, and the ion energy is 300eV~1MeV. The implantation depth is several thousand Å. Under deep implantation, the surface layer becomes amorphous. The degree of damage and depth of the surface is determined by the implantation energy. In particular, the critical metric for sapphire amorphous transition is ~2 for 150 keV Cr ions implanted at ~77K or 300 keV Ni ions implanted at ~100K • 1015 cells/cm2. For 400 keV Xe ions the critical stoichiometry is 3 • 1016 cells/cm2 [86]. The damaged surface adjacent layer recrystallizes under post-implantation annealing at 873-1,873 K. migration and redistribution.

Unlike Mn, Ni or Xe ions, trivalent Cr, Ga and Fe ions can enter the sublattice sites of Al during annealing in air atmosphere. At 1,473K all Cr3+ ions enter the sublattice and no ions are observed further migration.

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