Raman scattering intensities in BaTiO3 and PbTiO3 prototypical ferroelectrics from density functional theory

in Journal of Physics : Condensed Matter (2009), 21

Nonlinear optical susceptibilities and Raman scattering spectra of the ferroelectric phases of BaTiO3 and PbTiO3 are computed using a first-principles approach based on density functional theory and ... [more ▼]

Nonlinear optical susceptibilities and Raman scattering spectra of the ferroelectric phases of BaTiO3 and PbTiO3 are computed using a first-principles approach based on density functional theory and taking advantage of a recent implementation based on the nonlinear response formalism and the 2n + 1 theorem. These two prototypical ferroelectric compounds were chosen to demonstrate the accuracy of the Raman calculation based both on their complexity and their technological importance. The computation of the Raman scattering intensities has been performed not only for the transverse optical modes, but also for the longitudinal optical ones. The agreement between the measured and computed Raman spectra of these prototypical ferroelectrics is remarkable for both the frequency position and the intensity of Raman lines. This agreement presently demonstrates the state-of-the-art in the computation of Raman responses on one of the most complex systems, ferroelectrics, and constitutes a step forward in the reliable prediction of their electro-optical responses. [less ▲]

Unusual behavior of the ferroelectric polarization in PbTiO3/SrTiO3 superlattices

in Physical Review Letters (2005), 95(17),

Artificial PbTiO3/SrTiO3 superlattices were constructed using off-axis rf magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ... [more ▼]

Artificial PbTiO3/SrTiO3 superlattices were constructed using off-axis rf magnetron sputtering. X-ray diffraction and piezoelectric atomic force microscopy were used to study the evolution of the ferroelectric polarization as the ratio of PbTiO3 to SrTiO3 was changed. For PbTiO3 layer thicknesses larger than the 3-unit cell SrTiO3 thickness used in the structure, the polarization is found to be reduced as the PbTiO3 thickness is decreased. This observation confirms the primary role of the depolarization field in the polarization reduction in thin films. For the samples with ratios of PbTiO3 to SrTiO3 of less than one, a surprising recovery of ferroelectricity that cannot be explained by electrostatic considerations was observed. [less ▲]

Nonlinear optical susceptibilities, Raman efficiencies, and electro-optic tensors from first-principles density functional perturbation theory

in Physical Review b (2005), 71(12),

The nonlinear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach ... [more ▼]

The nonlinear response of infinite periodic solids to homogenous electric fields and collective atomic displacements is discussed in the framework of density functional perturbation theory. The approach is based on the 2n+1 theorem applied to an electric-field-dependent energy functional. We report the expressions for the calculation of the nonlinear optical susceptibilities, Raman scattering efficiencies, and electro-optic (EO) coefficients. Different formulations of third-order energy derivatives are examined and their convergence with respect to the k-point sampling is discussed. We apply our method to a few simple cases and compare our results to those obtained with distinct techniques. Finally, we discuss the effect of a scissors correction on the EO coefficients and nonlinear optical susceptibilities. [less ▲]

First-principles study of the electro-optic effect in ferroelectric oxides

in Physical Review Letters (2004), 93(18),

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic ... [more ▼]

We first present a method to compute the electro-optic tensor from first principles, explicitly taking into account the electronic, ionic and piezoelectric contributions. We then study the nonlinear optic behavior of three paradigmatic ferroelectric oxides. Our calculations reveal the dominant contribution of the soft mode to the electro-optic coefficients in LiNbO3 and BaTiO3 and its minor role in PbTiO3. We identify the coupling between the electric field and the polar atomic displacements along the B-O chains as the origin of the large electro-optic response in perovskite ABO(3) compounds. [less ▲]

Electron localization in lithium niobate

in American Institute of Physics (2002)

Using a plane-wave pseudopotential approach to density functional theory, we investigate the degree of electron localization in lithium niobate. We pay a particular attention to its variation during the ... [more ▼]

Using a plane-wave pseudopotential approach to density functional theory, we investigate the degree of electron localization in lithium niobate. We pay a particular attention to its variation during the phase transition and to the relationship with the electronic structure and the Born effective charges in this material. A band-by-band decomposition allows us to focus on the different bands composing the energy spectrum of this compound. At variance with previous calculations based on finite differences, the localization tensor has been obtained using linear-response techniques. [less ▲]