Dresden 2006 – wissenschaftliches Programm
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DF: Dielektrische Festkörper
DF 9: Phase Transitions
DF 9.6: Vortrag
Donnerstag, 30. März 2006, 11:50–12:10, M{\"U}L Elch
Non-ergodic behavior of polar state in Li-doped KTaO3 under an electric field — •Yoshiaki Uesu1, Hiroko Yokota1, Taeko Oyama1, Charlotte Malibert2, and Jean-Michel Kiat2 — 1Department of Physics, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan — 2SPMS, Ecole Centrale Paris, Grande Voie des Vignes 9225 Chatenay-Malabry, France
Incipient ferroelectric KTaO3 doped with Li-3% was investigated in order to clarify the dipole state under electric field. Using optical second-harmonic generation (SHG) microscope, we observed a marked history dependence of SHG intensity through zero-field cooling (ZFC), zero-field heating (ZFH), field heating after ZFC (FH/ZFC) and FH after field cooling (FH/FC) for both crystals. At fixed temperature in FH/ZFC, the long relaxation process to the equilibrium state is observed dependent on temperature. In quite low temperature, the SHG does not develop under the electric field. This kind of non-ergodicity is known to be a character of inhomogeneous system. Further experiments are performed using precise X-ray diffraction method. It reveals that two-step transformation occurs: at 50K, remarkable field-induced SHG and photo-conductivity accompanied by tetragonal lattice strain occur, while at 90K, does only small lattice strain. The fact indicates that polar nano-regions generated at 90K in nonpolar cubic matrix are transformed into ferroelectric micro-domain state at 50K without field. Under an electric field, the micro-domain state is changed to macroscopic ferroelectric state.