OBSERVATION OF INTERNAL FIELD IN LITAO3 SINGLE-CRYSTALS - ITS ORIGIN AND TIME-TEMPERATURE DEPENDENCE

The measured polarization hysteresis loop for a Z-cut LiTaO3 crystal w as found to be asymmetric about the field axis indicating the presence of an in-built internal field in the crystal of 5 kV/mm in the direct ion of the original polarization in the virgin crystal. Upon polarizat ion reversal under electric field, the internal field tends to realign along the new polarization direction. Systematic time-temperature dep endence of this realignment process was carried out. At room temperatu re, this realignment process was incomplete even after many days, whil e above 200 degrees C, the recovery process takes less than 30 s. Cond uctivity measurements also indicate an exponential increase in the de conductivity of the sample above 200 degrees C with an activation ener gy of 1.55 eV. Further experiments related to the behavior of the inte rnal field with change in sample thickness and surface removal reveale d that the internal field is a volume effect. Possible origins of this field based on point defect chemistry of the crystal are discussed. ( C) 1996 American Institute of Physics.