Regensburg 1998 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 6: Poster

DF 6.2: Poster

Donnerstag, 26. März 1998, 09:30–12:30, A

Oxidation and reduction dependent properties of pure and doped incipient ferroelectrics KTaO₃ and SrTiO₃ — •J. Licher¹, Ch. auf der Horst¹, S. Eden¹, V. Vikhnin², and S. Kapphan¹ — ¹FB Physik, University of Osnabrück, Barbarastraße 7, D-49069 Osnabrück, Germany — ²Ioffe Institute, 194 021 St. Petersburg, Russia

The investigation of the incipient ferroelectric systems KTO and STO at low temperature with optical second harmonic generation (SHG) using Nd:YAG-lasers and luminescence shows a parallel behaviour. Both the SHG intensity and the integral intensity of the green luminescence increase drastically upon reduction and decrease upon oxidation. The results are interpreted in terms of inversion symmetry breaking and associated with oxygen defects which polarize soft lattice. These intrinsic dipole defects interact with dipoles introduced by doping (f.i. in Li⁺ doped KTO) resulting in strong changes of the dipolar ordering. The possible nature of intrinsic dipole defect is the electronic polaron or charge transfer vibronic exciton (CTVE) trapped by oxygen vacancies, both with two dipole orientations. Such centers increase the Li-Li dipole-dipole indirect interaction. The self-recombination of CTVE explains the green luminescence properties. The static and dynamic behaviour of the SHG intensity under applied electric field confirms the dipolar nature of the centers and allows to estimate the activation energy for reorientation. This work is supported by DFG (SFB 225/C7), NATO Linkage Grant HTECH LG960540 and DFG 436RUS113/341/1(R).