Raman spectra of crystalline iron perchlorate hexahydrate

Abstract

Raman studies of crystalline iron perchlorate hexahydrate (Fe(ClO 4 ) 2 ·6H 2 O) in the region of lattice and anion internal modes were carried out in the temperature range 80-385 K. The temperature-dependent Raman results are consistent with those from previous works, showing that two phase transitions occur around 336 and 245 K. The transition at 336 K may be considered as an order-disorder transformation, while the one at 245 K is associated with the configurational disorder of the tetrahedron of the perchlorate ions.

Raman scattering intensities in BaTiO3and PbTiO3prototypical ferroelectrics from density functional theory

“…On the one hand, it gives rise to the non-analytical part of the dynamical matrix that modifies the frequencies and eigenvectors with respect to pure TO phonons. On the other hand, the electric field induces an additional change in the dielectric susceptibility tensor related to the nonlinear optical coefficients χ (2) i jk . Thus, for LO phonons, equation (8) has to be modified as follows [16]:…”

“…Thus, the Raman calculation requires several ingredients, such as the vibrational frequencies and eigenmodes obtained from the diagonalization of D, as well as the Z * , ε ∞ , χ (2) and π tensors. All these quantities should be in relative good agreement with the experimental ones to have a reliable prediction on the Raman spectra.…”

“…The second-order nonlinear optical susceptibility, χ (2) , is a third-rank tensor related to the electronic response of the system and which depends on the frequencies of the optical electrical fields [22]. However, in the present context of the 2n + 1 theorem applied within the LDA to (static) DFT, we neglect the dispersion of χ (2) computing the electronic response at zero frequency.…”

“…The second-order nonlinear optical susceptibility, χ (2) , is a third-rank tensor related to the electronic response of the system and which depends on the frequencies of the optical electrical fields [22]. However, in the present context of the 2n + 1 theorem applied within the LDA to (static) DFT, we neglect the dispersion of χ (2) computing the electronic response at zero frequency. Within these conditions, the χ (2) tensor is related to a third-order derivative of a field-dependent energy functional, F = E − 0 E • P, where E, E and P are, respectively, the total energy in zero field, the macroscopic electric field and the macroscopic polarization [11].…”

“…Raman spectroscopy is a powerful experimental tool, nowadays routinely applied for the characterization of material properties [1][2][3][4][5][6][7]. The interpretation of the positions and intensities of Raman lines is usually not straightforward and calls for accurate theoretical support.…”