Gamma-Irradiation Effects in Single-Crystalline Barium Titanate

This study presents the results of an experimental investigation of Co⁶⁰ γ-irradiation effects in single-crystalline barium titanate. Two test groups of crystals were utilized in this study. Prior to being irradiated, one group was etched in phosphoric acid at 145^∘{}C to remove a surface layer having properties which differ from the bulk of the crystal. The second group of crystals was irradiated in the as-grown condition. Following irradiation at various γ doses, the ferroelectric hysteresis loop was determined, measurements were taken of the optical absorption spectrum in the wavelength range 0.43-0.70 {μ}, and photomicrographs of the domain structure were obtained. The temperature was maintained at 20^∘{}C during irradiation, and all post-irradiation measurements were made at 23^∘{}C. The etched crystals were irradiated in the poled condition to a maximum dose of 1.60×{}10⁹ rad. The remanent polarization Pᵣ was unaffected by a total γ dose of about 2×{}10⁸ rad. Irradiation to higher dose levels caused a reduction in Pᵣ. The coercive field Ec was reduced with initial irradiation. At a dose of about 5×{}10⁸ rad, a minimum value was reached and Ec then increased with continued irradiation. The domain structure of the c-domain crystals was unaffected by a total γ dose of 1.60×{}10⁹ rad. No absorption peaks were observed in the wavelength range studied as a result of Co⁶⁰ γ irradiation. The radiation-induced changes observed in the ferroelectric hysteresis loop of etched crystals cannot be attributed to changes in the domain structure or to the presence of point defects consisting of an oxygen vacancy with a single trapped electron. The unetched crystals were irradiated to a maximum dose of 2.91×{}10⁸ rad. With initial irradiation, the polarization reversal process was enhanced as the remanent polarization increased and the coercive field decreased. With increasing dose above 2×{}10⁷ rad, the hysteresis loop gradually deteriorated. The unetched crystals were found to be much more sensitive to Co⁶⁰ γ radiation than were the etched crystals.