Oxygen pipe diffusion in sapphire basal dislocation

The oxygen self-diffusion behavior in deformed sapphire single crystals (α-Al₂O₃) sapphire) with a high density of unidirectional basal dislocations was examined in the temperature range of 1424-1636°C using ¹⁸O isotopes and secondary ion mass spectrometry-depth profiling techniques. The pipe and lattice diffusion kinetics were best described by r²D_p = 4.6 × 10 ^-20 exp (-4.8[eV]/kT) [m⁴/s] and D₁ = 2.9× 10^-1 exp (-5.5[eV]/kT) [m²/s], respectively. Both the magnitude of pre-exponential factor and activation energy for oxygen pipe diffusion were in good agreement with that of indirect measurements of pipe diffusion deduced from the annihilation of dislocation dipoles. The measured bulk diffusion coefficient is also in good agreement with previously reported data having activation energies ranged between 5.5-6.1 eV.