[en] Zone-center optical phonons in ZrSe₃, the prototype of the IVsub(B)-trichalcogenides family, are investigated by Raman scattering for several incident and scattered light polarizations, and by infrared reflectance measurements. These layered compounds are characterized by isolated chains along the b-monoclinic axis formed by the linear stacking of distorted trigonal prisms with Se atoms at the corners and Zr atoms in the center. Nine modes are found among the twenty-ones theoretically predicted. Phonons assignment is made by a group theoretical analysis of the crystal structure, using the correlation method which relates single chain modes to crystal modes as the interchain coupling is turned on. (author)

[en] Resonant Raman experiments on first-order disorder-activated bands in Gasub(1-x)Alsub(x)As alloys are presented. Selective enhancements occur, in particular, in the acoustic region. These resonances enable to assign unambiguously the features revealed and to determine their mode behaviour. The enhanced disorder-activated bands are compared with the structures appearing in the Raman spectra of GaAs-AlAs superlattices

[en] Raman scattering measurements in the tetragonal Cd₃As₂ single crystals are carried out at temperatures of 300 and 77 K. The spectra obtained are interpreted in terms of phonon-electron and electron-electron interactions. The features in the low-frequency interval are due to contributions from phonon and single particle scattering. The electronic RS involving intra- and interband excitations is dominant at frequencies higher than 80 cm^-1. The resonant enhancement of the band at 300 cm^-1 arises from the incident light frequency being in the vicinity of Σ₁ - Σ₄. (author)

[en] Resonant Raman scattering is investigated around the fundamental edge E₀ in Ga/sub 1-x/In/sub x/P solid solutions. The strong enhancements of the 'forbidden' LO-like modes are explained by a Froehlich intraband interaction and lead to replica of the first-order spectra. The non-homogeneous activation of the one-phonon density of states and the unusual sharp enhancements of LA-like modes are interpreted as due to structural disorder effects. Local chalcopyrite arrangements are suggested. (author)

[en] The mode behaviour of long wavelength optical phonons in the ternary phase ZrSsub(3-x)Sesub(x) has been investigated by means of Raman spectroscopy through the whole composition range 0 <= x <= 3. A mixed one-, two- and three-mode behaviour is observed, depending respectively on modes of group I (quasi-rigid chain modes), II (internal deformation chain modes) and III (diatomic X-X [X = S,Se] stretching mode). Three-mode behaviour of diatomic X-X mode is explained in terms of vibrations of S-S, Se-Se and S-Se pairs, practically insensitive to metal atoms as shown by comparison with the HfSsub(3-x)Sesub(x) system. The analysis of integrated intensities of peaks assigned to vibrations of S-S, Se-Se and S-Se pairs on the basis of a statistical model concludes in favour of higher Raman efficiency of selenium pairs compared to sulfur pairs. On the other hand, one-mode behaviour of quasi-rigid chain modes establishes unambiguously a one-to-one mode correspondence between the two binary compounds, confirming thus our previous assignments. Spectral features of the ternary phase suggest contributions from the density of vibrational states due to relaxation of Raman selection rules resulting from configurational disorder. (author)

No abstract available

[en] The Raman spectra of ZrTe₅ are recorded at various temperatures between 10 and 500 K. The data give no evidence for a structural phase transition, in spite of appreciable temperature dependent effects in some of the Raman modes. The lack of Raman spectroscopic evidence for a low temperature structural phase transition in ZrTe₅ is also confirmed by powder X-ray and neutron diffraction data collected over 100 to 295 and 10 to 295 K, respectively. The present findings strongly suggest that the reported anomaly in the electrical resistivity at 141 K must reflect change(s) in the electronic band structure of ZrTe₅, and the temperature dependences of the Raman spectra could be caused by variations in the first order susceptibility. (author)

[en] Fresh Raman data collected from the (001) face of a ZrTe₅ single crystal and from polycrystalline powders of ZrTe₅ and HfTe₅ are presented. A simple model assuming only central interactions between nearest neighbour atoms is used for lattice dynamical calculations at k-vector = O-vector. The model accounts for the observations and places emphasis on the virtually lacking dynamical coupling between the two basic structural units in these pentatellurides [trigonal-prismatic (MTe₃)sub(n) rods and zig-zag (Te₂)sub(n) chains]. (author)

[en] Measurements of Raman spectra from US₃, USe₃ and UTe₃ are reported. Lines in the room-temperature spectra have been assigned to long-wavelength optical phonons by comparison with non-magnetic isostructural group IV_B transition metal trichalcogenides. New features which appear at low temperature have been attributed to low-lying electronic excitations within the 5f² configuration of U⁴⁺. This temperature-dependent behaviour may indicate the onset of antiferromagnetic ordering below 50 K in both US₃ and USe₃, in contrast with UTe₃ which is still a paramagnet on cooling to 10 K. (orig.)

[en] Infrared transmission measurements in CdSb were performed at 2 K using the Fourier Transform Spectroscopy (FTS) technique in the wave number region 30 to 300 cm^-1. A magnetic field up to 18 T was applied in order to distinguish lattice absorption from electronic excitations. A recording of the CdSb Raman spectrum supports the conclusions. The measurements show that the contribution of electronic excitation in the IR and Raman spectra is weak or absent and that the dynamical properties of CdSb are closely related to InSb ones