The composition dependence and new assignment of the Raman spectrum in lithium tantalate

The Raman scattering spectra of lithium tantalate crystals with different compositions were investigated. The comparison of the Raman data obtained for the congruent and the near-stoichiometric crystals reveals some differences in the shape and the number of Raman peaks, which lead to a new assignment of the long-wavelength optical phonons. And quantitative relationships between the linewidth of Raman peaks (142 cm−1 for E-phonon and 861 cm−1 for A1-phonon) and the crystal composition were firstly presented. Two local Raman lines, 278 and 750 cm−1, were found for the congruent crystals and attributed to the intrinsic defects, Li vacancy and anti-site Ta ion, respectively.