SECOND HARMONIC GENERATION AND POLARIZATION MICROSCOPE OBSERVATIONS OF QUANTUM RELAXOR LITHIUM DOPED POTASIUM TANTALATE

Polar state in a quantum relaxor K_(1−x)Li_xTaO₃ (KLT) is investigated using second harmonic generation (SHG) and polarization microscopes. Temperature dependences of SHG image and interference color image related to birefringence are observed on three different processes (zero field heating after zero field cooling, field heating after zero field cooling, and field heating after field cooling processes). A remarkable history dependence in the T-E space which is one of the characteristic behaviors of relaxor is observed in SHG and polarization microscope observations. Ferroelectric phase transition occurs below the transition temperature T_p with tiny domain structures which is beyond the optical microscope diffraction limit. Under an electric field, these micro domain structures change to macroscopic structures. Based on these experiments, we propose a polar state model of KLT below T_p.