No abstract

International audienc

The Raman spectrum of has been measured for various scattering configurations in crystals with different compositions. The comparison between spectra recorded for the congruent and the nearly stoichiometric crystals shows significant differences in the shape and the number of Raman peaks. The analysis of results leads to a new and complete assignment of the long-wavelength optical phonons in .

No abstract

Light scattering measurements are investigated as a function of temperature from 10 to900 Kin the tetragonal andcubicphasesofaPbTi0,crystal. Phononfrequencies, ionic effective charges, spontaneous polarization and contribution to the dielectric permittivity arededucedfromthesedata.Theresu1tsshowthat thesoft phononandrelaxationmode are both needed to describe the dynamics of this material.

Raman microprobe applied on LiNbO3 (LN) crystals and derived materials or devices is shown to be a tool to detect either local variations or changes of the whole structure. Position, width, or intensity of one Raman line can be used as markers of a structural change. Indeed, each Raman line can be assigned to a peculiar ionic motion and is differently sensitive to application of strain, temperature change, and electric field. Some vibrational modes are especially associated to the site of Li ion, or Nb ion, or still oxygen octahedron, so that they can be affected by the introduction of dopant ion on one or another site. Therefore, Raman Spectroscopy (RS) can be used as a site spectroscopy to describe the mechanism of doping incorporation in the LN lattice, allowing the optimization of some linear and non-linear optical properties according to the dopant concentration and substitution site. The composition or the content of non-stoichiometry related defects could be derived from the width of some lines. Any damage or local disorder can be detected by a line broadening. The quality or preservation of the structure after chemical treatment, or laser pulses, can be thus checked. The structure of ion-implanted or proton-exchanged wave-guides and periodically poled lithium niobate as well can be imaged from frequency shift or intensity change of some lines. RS is thus a useful way to control the structure of LN and/or to optimize the preparation parameters and its properties.

International audienc

No abstract