2ND-HARMONIC GENERATION AND THERMALLY STIMULATED DEPOLARIZATION CURRENT INVESTIGATION OF K1-XLIXTAO3

the incipient ferroelectric KTaO3 small substitutional Li-ions are kno wn to induce dipolar microgregions due to their off-center dipole mome nt. A sensitive method to observe the appearance of non-inversion symm etric regions in K1-xLixTaO3 is based upon monitoring the second harmo nic intensity (SHG) of Nd: YAG laser light. At low temperatures a cons iderable SHG intensity (calibrated with respect to LiNbO3) is observed with a characteristic temperature-, field- and Li-concentration depen dence. The time and temperature dependence of the electric field induc ed SHG intensity change shows an Arrhenius-like behavior with fast and slow relaxation processes. For concentrations larger that x approxima te to 0.02 the slow relaxation process with an activation energy of E( A) approximate to 86 meV has been interpreted as a reorientation of ma inly antiparallel ferroelectric domains. Measurements of the thermally stimulated depolarization current (TSDC), performed after removing th e bias field at LHe-temperature, yield for a x = 0.028 sample a broad current peak with a maximum at approximate to 60 K. A good fit to the experimental data can be reached for a distribution of relaxing dipole s according to a Havriliak-Negami model with a mean activation energy Delta A = 178 meV. The difference in activation energies will be discu ssed in terms of different reorientation processes.