<title>Thermostimulated electronic and ionic processes in irradiated sapphire</title>

Abstract

Electronic and ionic thermostimulated (TS) relaxation (TSR) processes in nominally pure sapphire (α-Al₂O₃ grown with oxygen deficiency) have been investigated at 290 - 650 K by means of the TS current (TSC), ionic depolarization current (TSDC) and electron emission (TSEE) techniques. After thermal (ionic) polarization of the reduced sapphire wide (approximately 75 K) and asymmetric ionic dipolar TSDC peak at 590 K (disorientation of the anion vacancy-related dipoles) was detected. Above 450 - 500 K the anion vacancy hopping (migration) starts and their interaction with defects take place. This can lead to lattice dynamic disordering and anion vacancy diffusion-controlled processes in sapphire (especially -- in vacuum near the sample surface, grain boundaries, dislocations) in various TSR (TSC, TSDC, TSEE, TS heat release and bleaching) phenomena. The ionic TSDS peak at 590 K correlates with the wide TSEE peak at 615 K, with the rise stage of the radiation-induced electrical degradation (RIED) above 550 K (maximum at 745 K) and the chromium emission line broadening in ruby. The REID effect (observed above 550 K by E. R. Hodgson et al.), colloid formation and structure change of sapphire are caused by oxygen exchange at the grain boundaries, surfaces, dislocations and impurity-rich regions. Surface structure, impurity content, surrounding atmosphere (vacuum or air) and electric fields determine these phenomena.