The Study Of Electro-optic Response Of Potassium Tantalate Niobate Crystal Near Phase Transition Temperature

Potassium tantalate niobate(KTa_1-xNb_xO₃,KTN)crystal is an excellent electro-optic（EO）material for optical devices due to its enormous quadratic electro-optic（QEO）effect near the Curie temperature.Generally,ferroelectric domain in KTN is considered to be responsible for the excellent electro-optic performances.However,there are rarely study on the ferroelectric domain observation and mechanism analysis of origin of this giant QEO effect.This paper mainly studies the electro-optic dynamic response performance of ferroelectric domain in KTN under various temperature and electric field intensity in KTN crystal,then analyses the evolution of the ferroelectric domain near the phase transition temperature process.Basic physical properties of the KTN crystal has been studied.The dielectric measurement system was used to characterize the dielectric property of KTN crystal by the dielectric abnormal phenomenon,then the composition of crystal samples has been obtained.Relaxation factor was calculated,describing the deviation of dielectric constant from the Curie-Weiss’ s law,and verified the existence of ferroelectric domains near Curie temperature.The hysteresis loop of the crystal is measured to characterize the ferroelectric properties,and characteristic parameters,which can provide theoretical basic for poling process and EO experiment,such as the coercive field and spontaneous polarization were obtained.The dynamic response of ferroelectric domains in KTN crystals under various temperature was studied.A Senamont single beam compensation system was constructed to measure the linear and quadratic electro-optic coefficients of a polarized KTN crystal during heating.Fourier transform was used on time domain output voltage signal wave to obtain frequency domain signal wave,in which we found that the output signal was composed of two parts,linear electro-optic effect and quadratic electrooptic effect.Polarizing microscope was used for the observation of ferroelectric domains of KTN crystals.Polarization characteristics of KTN crystals before and after polarization were analyzed under both heating and cooling process to study the evolution of ferroelectric domain.The dynamic response of the ferroelectric domain in the KTN crystal under various ac/dc electric field near Curie temperature was investigated.The linear and quadratic electro optic coefficients under various electric field intensity was measured by single beam compensation method.The experimental results before and after polarization were compared under different temperature conditions.The field-induce orientation and binding effects of polarization treatment on ferroelectric domains were explained by phenomenological Landau theory,to explain the mechanism of dynamic response of EO effect.