Abstract
The pyroelectric current spectrum (P.C.S.) measured in iron-doped barium titanate shows new features which can be explained taking into account a static pseudo Jahn-Teller effect both at trapped-electron defect centres (T.E.D.C.) and at photoexcited electron defect centres (P.E.D.C). Furthermore it is necessary to introduce a polaronic exchange between T.E.D.C. and P.E.D.C. (The role of the dynamic part of the Jahn-Teller effect does not have to be considered although it is not necessarily weak.) The static part of this effect is introduced by the interaction of a single phonon mode and a two-electronic level system. The contribution of this effect is found greater at T.E.D.C. than at P.E.D.C. The model differs from the latest ones proposed for barium titanate (Fridkin) and for lithium niobate (Staebler) so far as they do not include the Jahn-Teller effect but rather macroscopic internal fields. Our model does not exclude this last possibility.
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