Measurement of the BaTiO₃ domain structure by using ultrahigh-vacuum atomic force microscopy (UHV-AFM)

We report the nanoscopic properties of the clean, free surface of a BaTiO₃ single crystal in an ultra-high vacuum. Atomic force microscopy, piezoelectric force microscopy and Kelvin force microscopy measurements show that the potential difference between upward and downward 180° domain is approx 100 mV. This value is 100 times smaller than the value estimated by using the standard 180° domain theory. Furthermore, our experiments show that this result cannot be explained only by the conventional explanations (that is, a decrease in the depolarization field by closure domains, the compensation of polarization bound charge by contamination or by oxygen excess and deficiency or ion transport). The results suggest a possibility that an intrinsic electrostatic shielding mechanism exists in the ferroelectrics and is essential for 180° domains.