Electric field induced domain rearrangement in potassium niobate thin films studied by in situ second harmonic generation measurements

We report a sensitive technique to study domain rearrangement in ferroelectric thin films using in situ second harmonic generation (SHG) measurements. The following film system on a MgO substrate was studied: KNbO3(110)parallel to 120 Angstrom SrTiO3 (100)parallel to MgO(100).(100). From x-ray diffraction, four possible domain variants in the film growth plane were determined to be KNbO3[1(1) over bar0$]parallel to SrTiO3 and MgO[001], [00(1) over bar], [010], or [0(1) over bar0$] denoted as variants X+, X-, Y+ and Y-, with area fractions A(X+), A(X-), A(Y+) and A(Y-), respectively, in the film growth plane. The SHG signal (532 nm) from the films generated by a transmitted fundamental beam of 1064 nm was measured and theoretically correlated to the area fractions of different domain variants in the film. The magnitude and signs of net area fractions (A(X+)-A(X-)) and (A(Y+)-A(Y-)) were determined as a function of external field applied along the MgO[001] direction in the film growth plane. No remnant poling was observed in KNbO3 films after application and removal of external fields up to 10 kV/cm at room temperature. We propose mechanisms to correlate this behavior to the pinning of domain wall motion by low angle grain boundaries in KNbO3. (C) 1997 American Institute of Physics.