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DF: Dielektrische Festkörper

DF 6: Poster

DF 6.4: Poster

Mittwoch, 28. März 2001, 14:30–18:00, Foyer S3

SHG properties of pure and doped incipient ferroelectrics KTaO₃ and SrTiO₃ under applied electric fields — •J. Licher¹, C. auf der Horst¹, S. Kapphan¹, V. Vikhnin², and S. Prosandeyev³ — ¹FB Physik, University of Osnabrück,Barbarastraße 7, D-49069 Osnabrück, Germany — ²Ioffe Institute, 194 021 St. Petersburg, Russia — ³Rostov-Don State University, Rostov-Don, Russia

The investigation of the incipient ferroelectric systems KTaO₃ (KTO) and SrTiO₃ (STO) at low temperature with optical second harmonic generation (SHG) using a Nd:YAG-laser shows a similar behaviour. The SHG intensity S increases drastically upon reduction and conversely decreases upon oxidation. The results can be interpreted in terms of inversion symmetry breaking dipolar centers associated with oxygen defects which polarize increasing regions of the surrounding lattice with decreasing temperature. These oxygen defect related centers interact with dipolar centers introduced by doping (f.i. in Li⁺ doped KTO) resulting in strong changes of the dipolar 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. The SHG signal S of nominally pure, but containing oxygen defect related dipole centers, KTO first is proportional to E (S = bE). For Li-doped KTO the b-coefficient increases strongly with increasing Li-doping in comparison with nominally pure KTaO₃. At moderately higher E-fields the SHG intensity S appears to be saturated in agreement with recent theoretical model calculations.