Abstract

A recent paper by Klein and Schwartz (1) discuss the photorefractive effect mechanisms (PRE) in commercial BaTiO₃ samples in terms of Fe²⁺ and Fe³⁺ impurities. The results of various experimental techniques (RPE, beam compling, absorption) lead them to conclude that the usual two level model involving the Fe²⁺ to Fe³⁺ conversion is sufficient to explain PRE. As their interpretations invoke molecular orbital calculations relevant to iron centers in various perovskite hosts (see ref.² for instance), a more complete study of the electronic structures of possible centers responsible of PRE in BaTiO₃ is presented in this paper. To this end, we report in figure 1 the electronic levels of Fe²⁺, Fe³⁺ ions trapped in tetragonal BaTiO₃ as well as the ones relevant to neutral and single ionized oxygen vacancies. The calculations are based on the MS-Xx method as described in ref. ². They assume that iron substitutes exactly Ti⁴⁺ in its tetragonal site, without additional relaxation or distortion of the lattice around the impurity ; near a V_o site, Ti⁴⁺ is assumed to be displaced by about 0.2A° towards V_o. We concentrate now on the possible centers responsible of PRE.

© 1987 Optical Society of America