Raman studies of ferroelectric domain walls in lithium tantalate and niobate

Using confocal Raman spectroscopy at low temperature we investigated the perturbation of the phonon modes across a domain wall region as a function of sample stoichiometry in lithium tantalate and niobate. For all samples, we found that the Raman spectra were changed. The intensity of the A(LO) phonon modes and most of the E(TO) phonon modes were shifted and changed in their relative intensity over a 20 μm length scale. Our measurements suggest that the intensity of the A(LO) phonon modes change due to local charges induced by pyroelectric effect and/or photoionization, while the observed shifts are due to strains that are not relaxed in the domain wall region. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)