Publication No.19 A. Stashans, H. Pinto. Analysis of radiation induced hole localisation in titanates - 4th Europ. Conf. Luminescent Detectors Transformers Ionizing Rad., Jurmala (Latvia), 2000, p. 103. Abstract: Light-induced charge-transfer processes determine the majority of important properties of the perovskite-type BaTiO3 and SrTiO3 crystals. A number of experimental works suggest that trapped holes are significantly involved in all relevant radiation-induced charge-transfer reactions in these titanates. However, the holes referring to shallow levels are identified with O- type centres trapped at suitable acceptor imperfections. The crucial supposition is that only impurity atoms can act as traps for the positively charged hole centres. By means of the modified for crystals quantum-chemical method [1] and analytical considerations [2] we study the possibility of self-trapped hole (STH) occurrence in pure BaTiO3 and SrTiO3 crystalline lattices, i.e., the possibility of negative O ions to act as traps. Our studies are based on the energetical favourability principle and lead us to the conclusion of the STH occurrence only in the BaTiO3 crystal under irradiation. The obtained results show preference of the one-centre hole configuration. The lattice distortion due to the defect presence is obtained considering various ways of atomic displacements. The absorption energy of the STH is obtained using the DSCF method and the equilibrium atomic configuration. The calculated value of absorption energy for STH in BaTiO3 is found to be equal to 0.50 eV, which is very close to the experimental value of 0. 53 eV for the absorption band obtained in undoped BaTiO3 crystal [3]. Thus our results are strongly supported by the radiation -induced absorption spectra measurements in undoped and Rh-doped barium titanate [3]. Using our model and a number of experimental works the phenomenon of the non-linear photoconductivity is discussed. Different photoconductivity behaviour between two materials is also analysed. 1. Stefanovich, E., Shidlovskaya, E., Shluger, A., Zakharov, M. (1990) Phys. Status Solidi B 160, 529-540. 2. Kantorovich, L., Stashans, A., Kotomin, E., Jacobs, P. W. M. (1994) Int. J. Quant. Chem. 52, 1177-1198. 3. Song, H., Dou S. X., Chi, M., Gao, H., Zhu, Y., Ye, P. (1998) J. Opt. Soc. Am. B 15, 1329-1334.
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