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 was 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 direction of the original polarization in the virgin crystal. Upon polarization reversal under electric field, the internal field tends to realign along the new polarization direction. Systematic time-temperature dependence of this realignment process was carried out. At room temperature, this realignment process was incomplete even after many days, while above 200°C, the recovery process takes less than 30 s. Conductivity measurements also indicate an exponential increase in the dc conductivity of the sample above 200°C with an activation energy of 1.55 eV. Further experiments related to the behavior of the internal field with change in sample thickness and surface removal revealed that the internal field is a volume effect. Possible origins of this field based on point defect chemistry of the crystal are discussed.