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Internal field in lithium tantalate single crystals

An in-built internal field of 5 KV/mm was measured in Z-cut LiTaO3 single crystals in the direction of the original polarization. This was reflected in the asymmetry (along the field axis) in the polarization hysteresis curve as a function of external electric field. Measurement of internal field as a function of crystal thickness revealed that the internal field is a volume effect. Using infrared absorption measurements, the spectrum of the hydroxl ions (OH-) present in these crystals was measured at room temperature. The shape of the spectrum changes with polarization reversal in these crystals indicating a strong correlation with the direction of internal field with respect to the polarization direction. It suggests that the origin of internal field lies in point defect complexes involving OH- ions.