Microscopic Observation of Ferroelectric Domains in SrTiO3 Using Birefringence Imaging Techniques under High Electric Fields

Phase transitions in SrTiO3 between quantum paraelectric, coherent paraelectric, and electric-field-induced ferroelectric states are governed by tetragonal domains with quantum fluctuations. However, their characteristics are still unclear. To observe the electric-field-induced ferroelectric state using birefringence imaging techniques, we developed a suitable sample holder to apply high electric fields of up to E similar or equal to 5 kV/cm and temperatures down to T = 20 K. From birefringence imaging measurements of the ferroelectric LiNbO3 with varying electric field, distributions of the electric field in the sample stage were found to be negligible. In SrTiO3, a huge-retardance area corresponding to the ferroelectric domains appears at E > 2kV/cm and T <= 60K even though the paraelectric domains partially remain. Furthermore, the fast-axis direction rotates by 90 degrees at the ferroelectric phase transition because of an electrostrictive effect in ferroelectrics. The phase diagram of the critical electric field and temperature agrees with previous reports obtained from dielectric and neutron scattering measurements.