Münster 1997 – scientific programme

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DF: Dielektrische Festkörper

DF 5: Störstellen, Inhomogene Medien

DF 5.2: Talk

Tuesday, March 18, 1997, 16:50–17:10, R2

Light-induced charge transport in BaTiO₃:Fe — •A. Mazur, R. Scharfschwerdt, and O. F. Schirmer — Fachbereich Physik, Universit"at Osnabr"uck, 49069 Osnabr"uck

Using EPR and optical absorption simultaneously, we have studied the absorption and the light-induced charge transport characteristics of BaTiO₃:Fe at room and cryogenic temperatures. We have also investigated the effect of thermal annealing on iron as well as the charge transport changes after such treatments.

The conversion of Fe⁴⁺ to Fe³⁺ occurs with the highest efficiency with light of ∼ 2.8 eV whereas the absorption transforming Fe⁵⁺ to Fe⁴⁺ is peaked near 2.5 eV. Under these illuminations valence band holes are created, which at low temperatures are captured at shallow acceptors such as (Na⁺, K⁺, Pt^x+)-O^–. The thermal levels Fe³⁺/Fe⁴⁺ and Fe⁴⁺/Fe⁵⁺ are closer to the valence band, ∼ 1 eV and below, indicating sizeable Franck-Condon shifts.

The role of Fe in reduced BaTiO₃ will also be discussed.