Raman scattering from La y R x MnO 3-δ compounds (single crystals, ceramics, films) was studied as a function of kind (R) and amount ( x ) of dopant as well as of oxygen deficit (δ). For x = 0.1 to 0.55, a nearly linear Raman shift of the A g mode from 240 to 125 cm −1 was observed in Srdoped compounds. While the intensity of disorder-induced Raman bands was found to be sensitive to the oxygen content, the symmetry allowed related Raman modes exhibit the changes in the frequency. As an indication of deposition conditions, lowering of a symmetry of the film structures with respect to single crystals and ceramics was detected. We discuss the physical nature of the observed effects and show how Raman data can be used for the optical characterization of manganite samples.

Polarized Raman spectra of undoped and doped La1-xMxMnO3 single crystals have been studied in the temperature range from 5 to 423 K (M=Sr, Ca). The spectral intensity is mainly related to scattering by optical phonons at q similar to 0 (for x approximate to 0) and the density of vibrational states for x>0.1. Raman spectra from the undoped LaMnO3 structure distorted by the static Jahn-Teller effect are consistent with the orthorhombic D-2h(16), space group. Raman spectra of the doped La1-xMxMnO3 crystals have weakly resolved features and intensities comparable to those of the second-order spectra in cubic media. The anomalies in the phonon spectra of doped crystals were explained by the doping dependence of the ionic radius of a La/Sr site. The most intense B-1g mode in LaMnO3 crystal has an abrupt frequency shift near T-N = 140 K, which corresponds to a paramagnetic to canted-antiferromagnetic phase transition. [S0163-1829(98)06725-3].

The properties of ferroelectric films are known to degrade when subjected to hydrogen in forming gas anneals. Earlier studies have attributed this degradation to the loss of oxygen from these films during these anneals. In this study, we show that though oxygen is lost during forming gas annealing, hydrogen incorporation is the primary mechanism for the degradation of ferroelectric properties. Raman spectra obtained from the forming gas-annealed films show evidence of polar hydroxil [OH−] bonds in the films. The most probable site for hydrogen ions is discussed based on ionic radii, crystal structure, electrical properties, and Raman spectra. We propose that the hydrogen ion is bonded with one of the apical oxygen ions and prevents the Ti ion from switching. Pyroelectric measurements on forming gas-annealed capacitors confirm that the capacitors no longer possess spontaneous polarization.

The temperature (6-350 K) and magnetic-field dependence (0-7.5 T) of the phononic Raman spectra in the layered manganites, R1.2Sr1.8Mn2O7 (R = La,Nd), reveal anomalous behaviors of the Mn and equatorial O-xy(Big) modes arising from local octahedral distortions and coupling to the Mn3+ e(g) electrons. These results provide the evidence for polaron formation and its interplay with electrical transport and magnetism in the layered manganites.

We report polarized Raman spectra of La1−xSrxMnO3 crystals (x = 0, 0.1, 0.2 and 0.3) in the temperature range from 5 K to 300 K. The small distortion of the nearly cubic lattice of doped La1−xSrxMnO3 single crystals results in a structured phonon Raman spectrum which is composed of two parts with different contributions depending on the value of doping. The first part is assigned to the distorted non-cubic perovskite lattice and follows the selection rules for a tetragonal structure. This suggests the possible presence of a tetragonal structure in doped La1−xSrxMnO3 single crystals. The second part is mainly due to the density of vibrational states and is attributed to the second-order Raman scattering. The frequency of the A1g-like mode was found to be sensitive to doping but the observed shift is opposite to that expected from the difference in the atomic weight of Sr and La. This mode exhibits also an anomalously large shift of ∼20 cm−1 in the temperature range from 5 K to 300 K. A possible explanation of this behaviour is suggested.

Polarized Raman scattering by phonons is used to characterize thin films prepared by laser ablation of La1−xCaxMnO3 targets. It was found that, in the temperature range from 6 to 300 K, phonon spectra of La0.7Ca0.3MnO3 films exhibit observable differences from those in bulk materials (microcrystalline ceramics and single crystals). A significant difference was found in the spectra of “as-grown” films compared to those annealed in oxygen at 800 °C. The observed Raman peaks and their linewidths exhibit an irregular temperature dependence near Tc. A correlation of Raman data with magnetization of the sample was also found.

Refractive-index fluctuation in As2Se3 under excitation by an Ar+ laser was measured by an optical grating method. After 50 min exposition with a power of 9.5 mW and diameter of the spot of ∼ 0.25 mm, the diffracted signal became considerably noisy. The Fourier transform of the signal reveals a 1ω spectrum, predicted for self-organized (ordered) electron-hole systems.

A magneto-Raman study of a YBa 2 Cu 3 O 7-δ single crystal (T c = 92 K) was carried out at a resolution of 2 cm -1 over the temperature range 5–125 K. At temperatures below T c we observed a slight narrowing of the 340 cm -1 Raman mode in a magnetic field of 5.15 T directed parallel to the c -axis of the crystal. The observed magneto-temperature dependences of the Raman continuum intensity measured in the low-frequency region, at ca. 40 cm -1 , indicate contributions of electronic excitations arising from a pair-breaking process. Within the experimental uncertainty, the Raman intensity of the high-frequency continuum was observed to be independent of the magnetic field strength.

Experimental studies of hyper-Raman scattering (HRS) in inorganic oxide glasses are reported. The observation of dipole-active modes in HRS shows the strong dependence of vibrational spectra on both the value and orientation of momentum transferred to the vibrational system. The conservation of momentum in the scattering process confirms the delocalization of vibrational modes in glasses. The peculiarities of the observed spectra (the polarization and angular properties, the absence of dipole-active modes in RS) are well explained by the macroscopic symmetry of glass. The excitation of HRS by two-frequency radiation enables the structure of the HRS vibrational spectrum to be defined. The first observation of HRS in a silica fibre is presented. This helps to overcome the problem of the extremely weak HRS signal strengths.

A Raman and a first hyper-Raman study of pure silica and Ge-doped silica fibers is performed. The Raman spectra of a doped fiber are accompanied by a broad luminescence band corresponding to charge transfer excitons of Ge-centers. Self-organization (orientational ordering) of these excitons under light pumping results in an instability of the system with respect to the weak static phase matched field ∼χ(3)E2ωEω∗Eω∗ found by Stolen and Tom. A fiber makes a transition into a polarized state accompanied by the strong phase matched field Edc ∼ ei(k2ω − 2kω)z allowing the second harmonic generation (χ(2) = χ(3)Edc, Edc ∼ 105 V/cm) to occur.

Theoretical and experimental studies of vibrational modes in the (Zn, Cd)Se/ZnSe quantum wells and ZnSe films are presented. The space distribution of electric field accompanying the quasi-transverse vibrations and hence the intensity of corresponding Raman line depends considerably on the thickness of the layers. The quasi-longitudinal vibration and its Raman intensity are insensitive to the thickness. These quasi-transverse and quasi-longitudinal modes give the main contribution to the Raman spectra of the (Zn, Cd)Se/ZnSe quantum wells.

Chalcogenide glasses As 2 Se 3 and As 2 S 5 are studied by optical methods. An optical grating is generated at the surface of the samples, and as a result a long-lived refractive index grating is created. Temporal appearance and decay of the diffracted beam power follow the refractive index change Δn(t) and this allows direct study of the Δn(t) behaviour. The electron-hole states with different degree of ordering are studied. It is found that the more ordered states have the slower decay.

We present an experimental evidence of the strong electron-hole correlation in As2Se3 glass under light pumping. The correlations of electrons and holes trapped in amorphous semiconductors manifest themselves in the recombination rate: the stronger the correlations, the weaker the decay. States with the same electron-hole densities but with different degrees of electron-hole ordering were prepared. The strongly correlated states were found to be long living.