Radiation enhanced diffusion of Ti in $Al2O3$

Titanium bulk and dislocation diffusion coefficients at 1000 °C have been determined for Ti in single crystal $α-Al2O3(0001)$ for three types of samples: (i) Ti evaporated onto $Al2O3,$ (ii) $Ti+48$at 100 eV deposited onto $Al2O3,$ and (iii) $Ti+48$ at 100 eV deposited onto radiation damaged $Al2O3$ (damage inflected by implantation of $Ti+46$ at 7 keV). Diffusion penetration profiles were obtained by using secondary ion mass spectrometry depth profiling techniques. For the deposited and implanted $Ti+$ samples, the bulk diffusion coefficients (D) are $5.4×10−21$ and $5.6×10−17 m2 s−1,$ respectively, and dislocation diffusion coefficients are $3.6×10−17$ and $1.4×10−12 m2 s−1,$ respectively. Comparing the D's for Ti in the undamaged and damaged $Al2O3,$ the D's for the latter samples are higher by a factor of $104–105,$ reflecting the radiation enhanced diffusion due to the defect structure inflected by the implanted 7 keV $Ti+46.$ Comparing the D's for Ti deposited onto $Al2O3$ (both the evaporated and 100 eV $Ti+48$ samples) with those for Cr deposited onto $Al2O3,$ the Ti D's are larger by a factor of 10, reflecting the influence of the valence state of the cation. These results show that cationic diffusion coefficients in $Al2O3$ can be controlled by varying the level of defects in the crystal.