Chromium diffusion coefficients in alumina single crystals were evaluated from penetration profiles determined by the SIMS technique. The samples were previously annealed at 1000°C (1 hour), 1500°C (4 hours), and 1700°C (24 hours). Diffusion experiments were carried out at 1400°C during 10 hours.
The results show that bulk diffusion coefficients are strongly dependent on preannealing conditions (temperature and time): they decrease by more than an order of magnitude when the preannealing temperature is increased from 1000°C to 1700°C.
These results are discussed taking into account the dislocations and point defects in alumina. We consider the role played by the linear defects resulting from surface polishing, as well as point defects associated with impurities. It is found that the lowest defect concentration is achieved after an annealing treatment at 1700°C during 24 hours. The conditions for obtaining a, «reference material» are proposed.