Nanoscale piezoelectric response across a single antiparallel ferroelectric domain wall

Surprising asymmetry in the local electromechanical response across a single antiparallel ferroelectric domain wall is reported. Piezoelectric force microscopy is used to investigate both the in-plane and out-of- plane electromechanical signals around domain walls in congruent and near-stoichiometric lithium niobate. The observed asymmetry is shown to have a strong correlation to crystal stoichiometry, suggesting defect-domain wall interactions. A defect-dipole model is proposed. Finite element method is used to simulate the electromechanical processes at the wall and reconstruct the images. For the near-stoichiometric composition, good agreement is found in both form and magnitude. Some discrepancy remains between the experimental and modeling widths of the imaged effects across a wall. This is analyzed from the perspective of possible electrostatic contributions to the imaging process, as well as local changes in the material properties in the vicinity of the wall

Determining electro-optic coefficients for lithium tantalate using an electro-optic scanning device

We demonstrate a ferroelectric optical device based on single crystal LiTaO{sub 3} that can scan a laser beam from the visible to the infrared. It utilizes the electro-optic effect in the ferroelectric that has potentially high intrinsic response times of GHz. There are many applications to such scanning devices in the infrared such as optical switching, spectrometry, microscopy, and sensing. Lithium tantalate has two ferroelectric polarization states that are antiparallel (180{sup o}) to each other. The domain states can be reversed by applying an electric field of {approx}21 kV/mm at room temperature. By reversing the domain structure in the crystal, we can create domains in the crystal of almost any desired shape. By creating prism-shaped domain, we can create a ferroelectric deflector or scanner by applying either static or sweeping voltages across the crystal. This scanner is capable of scanning wavelengths from 0.4-5 {micro}m. The scanning performance varied from a total deflection angle of 13.38{sup o} at 1558 nm to 16.18{sup o} at 632.8 nm. Since the amount of deflection of the incoming light is determined by the applied voltage, the electro-optic coefficient and other fixed quantities, by measuring the deflection angle as a function of wavelength, the dispersion of the electro-optic coefficient in lithium tantalate can be determined. In these experiments, the scanner was characterized from the visible (632.8 nm) to midinfrared (1558 nm). Both extraordinary and the ordinary polarizations of light were used, in order to determine the electro-optic coefficients, r{sup 33} and r{sup 31}. Except for the values at 632.8 nm, these values of the electro-optic coefficients have not been previously reported. For lithium tantalate, r{sup 33} at 632.8 nm is reported in the literature as 30.2 pm/V. We found that this decreases to 27.1 pm/V at 1558 nm. For the extraordinary polarization, r{sup 13} varied from 7.55 pm/V (632.8 nm) to 6.84 pm/V (1558 nm)