Evidence for local lattice distortions in giant magnetocapacitive CdCr2S4

Raman scattering experiments on CdCr2S4 single crystals show pronounced anomalies in intensity and frequency of optical phonon modes with an onset temperature T*=130 K that coincides with the regime of giant magnetocapacitive effects. A loss of inversion symmetry and Cr off-centering are deduced from the observation of longitudinal optical and formerly infrared active modes for T<T_c=84 K. The intensity anomalies are attributed to the enhanced electronic polarizability of displacements that modulate the Cr-S distance and respective hybridization. Photo doping leads to an annihilation of the symmetry reduction. Our scenario of multiferroic effects is based on the near degeneracy of polar and nonpolar modes and the additional low energy scale due to hybridization.Comment: 4 pages, 6 figure

Recent advances on thermoelectric materials

By converting waste heat into electricity through the thermoelectric power of solids without producing greenhouse gas emissions, thermoelectric generators could be an important part of the solution to today's energy challenge. There has been a resurgence in the search for new materials for advanced thermoelectric energy conversion applications. In this paper, we will review recent efforts on improving thermoelectric efficiency. Particularly, several novel proof-of-principle approaches such as phonon disorder in phonon-glasselectron crystals, low dimensionality in nanostructured materials and charge-spin-orbital degeneracy in strongly correlated systems on thermoelectric performance will be discussed.Comment: 12 pages, 12 figure

RAMAN SCATTERING IN FERROELECTRICS

Dans cet article, nous passons en revue l'effet Raman dans les ferroélectriques et les matériaux voisins.This paper gives a review on Raman effect in ferroelectrics and related materials

CRITICAL PHENOMENA IN SbSI

Des phénomènes critiques ont été trouvés dans SbSI. Particulièrement, on a observé une opalescence critique (diffusion Rayleigh) en proximité de la transition de phase.Critical phenomena are reported for SbSI. In particular it is observed that critical Rayleigh scattering (critical opalescence) occurs near the phase transition