Hyper-Raman tensors of the zone-center optical phonons inSrTiO3andKTaO3

Abstract

We measure the relative intensities of the seven hyper-Raman (HR) lines of SrT&03 and KTa03 at room temperature as a function of the scattering geometry. From our experimental data we deduce relative values of the HR tensor elements. There are two different HR tensor elements for each TO and LO component of the three Fl"phonons and one for the silent mode of symmetry type F2".Taking the phonon eigenvectors and longitudinal effective charges from improved versions of Cowley's shell model, we obtain the derivatives BP';ii'/Bu (v) and BX';,i'/BE of the second-order susceptibility with respect to the displacements of the five sublattices and the macroscopic electric field of the LO phonons, respectively. We interpret the parameters BX'"i'/Bu (~) in terms of a nonlinear bond-polarizability model and confirm the dominant role of the Ti-0 and Ta-0 interactions in the nonlinear-optical response.

Raman scattering spectra of ceramics, films, and superlattices of ferroelectric perovskites: A review

“…As was shown above, in the crystal and ceramics of the ST compound, the frequency of the TO 1 soft mode is equal to 88 cm -1 at room temperature [28], and as the temperature decreases, it is softened so that the extrapolation of the temperature dependence suggests T C = 32 ± 5 K [30]. In the PST70 ceramic sample, the frequency of the TO 1 soft mode is 25 cm -1 at 300 K, and it is softened to 20 cm -1 at the temperature T m = 283 K. The appearance of forbidden polar modes in the Raman spectra of the PST70 ceramic samples at temperatures above T m is associated with the presence of nanoscale polar regions.…”

“…The longitudinal optical modes correspond to the bands LO 1 (171 cm -1 ), LO 3 (474 cm -1 ), and LO 4 (792 cm -1 ). The frequency of the IR inactive mode of the F 2u type, according to the hyper Raman scattering [28], is equal to 266 cm -1 and corresponds to the LO 2 and TO 3 components. Below T a = 105 K, the IR spectra of the ceramic samples exhibited the E u mode activated from the R point as a result of the folding of the Brillouin zone due to the antiferrodistorsive transition.…”

Raman Spectroscopy of Ferroelectric Thin Films and Superlattices

“…3, the spectra for three SrTiO 3 films of different thicknesses measured at T =5 K are shown together with the spectrum of an SrTiO 3 single crystal. By comparing with the hyper‐Raman results of bulk single crystals, 37,38 the strong peaks at 170 and 545 cm −1 were identified as due to the TO 2 and TO 4 phonons, respectively, and the weak peak at 264 cm −1 to the silent TO 3 mode. These peaks can be observed up to room temperature.…”

Coherent phonon generation and detection in ultrathin SrTiO3 grown directly on silicon

“…3(b)). This frequency is much lower than the reported hard optical phonon frequencies in unstrained SrTiO 3 [25][26][27]. One possible low frequency excitation is an acoustic phonon.…”