Infrared reflectivity results of YBa2Cu3O7x and SmBa2Cu3O7−x, in the tetragonal semiconducting phase, are reported. At least 10 of the 11 group theoretically allowed modes are observed, and the 11th may be observed in the Sm-material. Due to the fact that the modes are clearly resolved from each other, and, in some cases, have large shifts when Y is replaced by Sm, severial these modes can be assigned to definate vibrations. This and other aspects of the data are discussed.

The utility of Raman spectroscopy for the simultaneous determination of composition and strain in thin GexSi1−x layers has been investigated. Using data from the literature and new data for the strain shift of the Si-Si phonon mode presented here, we show how Raman spectra provide several different means of measuring composition and strain in samples as thin as 200 Å. We demonstrate that for largely relaxed layers with compositions near x=0.30, Raman scattering can measure the composition, x, with an accuracy of ±0.015 and the strain, ε, with an accuracy ±0.0025. The accuracy of the alloy composition obtained from Raman spectra is comparable or, in the case of very thin layers, superior to that measured by other techniques such as x-ray diffraction, electron microprobe, and Auger electron spectroscopy.

The structure of a strain relief region between a Si substrate and a low dislocation density Ge film has been measured by Raman spectroscopy. The composition of the structure has been determined with ≂1000 Å resolution in the growth direction, and the upper portions shown to be largely relaxed. The presence of microscopic inhomogeneities in these alloys is suggested.

We have used Raman scattering to evaluate thick epitaxial GexSi1-x, layers with 0.20 less-than-or-equal-to x less-than-or-equal-to 0.43 grown on Si (100) substrates. We show that a detailed consideration of the composition dependencies of the relative intensities of the various phonon modes can enhance the sensitivity of Raman scattering to variations in composition and strain. We find that samples are uniform on a scale of congruent-to 1 mum laterally and < 1000 angstrom in the growth direction.

We report accurate temperature dependent measurements of optic indices of refraction, the birefringence, and the strain in the ferroelectric tungsten bronze crystals Ba0.25Sr0.75Nb2O6 and two compositions of (Ba2−xSrx)2(K1−yNay)2(NbO3)10. These results are compared to our previous results in Ba0.4Sr0.6Nb2O6. From the experimental data, it appears that far above the ferroelectric Tc, up to a temperature Td, these crystals possess a local, randomly oriented polarization, Pd, with similar Td values, irrespective of their chemical composition and Tc. Various aspects of our understanding of the polarization behavior and other effects in this ferroelectric system are discussed.

We have measured the Raman spectra of single crystals of YBa2Cu3O7-gd as a function of oxygen concentration, that is Y123-Ox, where x varies from approximately 7 (superconducting) to 6 (insulating). We have made similar measurements on single crystals of Sm123, Gd123, and Ho123. The experimental results from all of these single crystals are very similar. Our single crystal results are in distinct disagreement with experimental results on ceramic of these same materials. For x=7 the usual five, c-axis polarized modes are observed; mode #5 occurs at ∼ 500 cm-1 and is primarily due to motion of oxygen atoms in the four-coordinated Cu chain. At oxygen contents near the metal-insulator (M-I) phase transition, the intensity of mode #5 rapidly decreases and disappears, being replaced by a strongly (zz) polarized mode at ≈ 600 cm-1. We assign the 600 cm-1 mode to oxygen atom vibration in the two-coordinated Cu “sticks”. At the oxygen content near the M-I phase transition, other weaker lower-energy modes appear and these are discussed. However, these modes disappear for oxygen content x≈6, where the approxiate number of symmetry allowed modes (five) is again observed.

X-ray photoemission spectra (XPS) and Raman measurements of Y1-xEuxBa2Cu3O7 and Eu1-xPrxBa2Cu3O7 are compared to those of Y1-xPrxBa2Cu3O7. It is shown that, with increasing x, the binding energies of the Ba core levels of Eu1-xPrxBa2Cu3O7 shift towards higher values as in Y1-xPrxBa2Cu3O7, while those of Y1-xEuxBa2Cu3O7 do not, despite similar changes in Ba-O interatomic distances in the latter two systems. Raman measurements of Y1-xPrxBa2Cu3O7 show a frequency increase of the Ba and apical-oxygen modes with increasing x, but a much smaller frequency increases in Y1-xEuxBa2Cu3O7. The XPS and Raman results reflect changes in the Ba-O hybridization and correlate with both the suppression of superconductivity in both Y1-xPrxBa2Cu3O7 and Eu1-xPrxBa2Cu3O7, and with the retention of superconductivity in Y1-xEuxBa2Cu3O7.

We report polarized Raman measurements on single crystals of YBa2Cu3Ox, Y123-Ox, as a function of oxygen content. For x=7 the usual five, c-axis polarized modes are observed; mode #5 occurs ∼500 cm−1 and is due to the oxygen atoms in the four-coordinated Cu chain. At oxygen contents near the metal-insulator (M-l) phase transition the intensity of mode #5 rapidly decreases and disappears, being replaced by a strongly (zz) polarized mode at ≈600 cm−1. Our results are in sharp disagreement with published Raman results on ceramics. We believe the 600 cm−1 mode is due to oxygen atom vibration in the two-fold coordinated Cu “sticks”. At the oxygen content near the M-l phase transition, other lower energy modes appear but they disappear for oxygen content x≈6 where the appropriate number (five) of symmetry allowed modes are again observed. A “drastic difference” in the phonon density of states between x=6 and x=7 has been obtained from inelastic neutron measurements. We believe that much of the difference in phonon frequencies is not due to a decrease in the force constants in going from x=6, to x=7, but is due to phonon differences resulting from the coordination changes of the chain-Cu atoms.

The indices of refraction in the cubic phase of a crystal of BaTiO3 doped with Fe, and one doped with Mn, as well as (Ba0.56Sr0.44)TiO3 are reported and compared to that of pure BaTiO3. In all cases similar precursor effects are seen approximately 100°C above Tc. Thus, this effect seems to be an intrinsic property of BaTiO3, and not directly caused by impurities. The connection of these effects to overdamped phonons is discussed.

We report infrared and Raman measurements of phonons in the recently discovered electron-doped superconductors ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$(Ce,Th${)}_{\mathit{x}}$${\mathrm{CuO}}_{4}$, and undoped ${\mathrm{Nd}}_{2}$${\mathrm{CuO}}_{4}$. Utilizing data from ceramics and ab-plane single crystals, we have identified all of the expected infrared-active modes (3${\mathit{A}}_{2\mathit{u}}$+4${\mathit{E}}_{\mathit{u}}$). We have also observed the Raman modes for motion along the c axis in the pure and doped materials. Based on our data and group theory, we assign the observed phonons. Finally, we compare the phonons in this class of materials to those of the related hole superconductors based upon ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$.

If a crystalline material possesses a center of symmetry, it cannot be ferroelectric. Also, its Raman active modes must occur at different frequencies from its infrared (IR) active modes; this is the Exclusion Principle. By studying single crystals and ceramics, we have determined the Raman and IR active phonon frequencles for atomic motion along the c-axis in YBa2Cu3O7-[ddot], both in the superconducting and semiconducting phases. The measured phonon frequencies are consistent with the Exclusion Principle, hence this material does not appear to be ferroelectric in either the superconducting or semiconducting phases.

Les spectres Raman des composes publies anterieurement semblent incorrects. Ces spectres sont obtenus quand les echantillons sont «brules» par le faisceau laser focalise et sont dus au La 2 O 3 . Des spectres similaires sont obtenus si Nd 2 CuO 4 est surchauffe. Le spectre est alors celui de Nd 2 O 3

In this paper we discuss some of the measurements and properties of materials that are crystalline ferroelectrics with a glassy polarization phase. We review measurements of the temperature dependence of the optical index of refraction, n(T), which were first used to observe these properties. Then we discuss a model of these polarization effects in terms of a local, randomly oriented polarization (Pr) that may occur hundreds of degrees above Tc. This local polarization is allowed by the strong breakdown of the translational symmetry that occurs in these systems. We also show how the temperature dependence of the strain, x(T), complements the n(T) results. Lastly, we discuss some recent x-ray and EXAFS measurements and how they are in agreement with the model, and the connection between these high temperature effects and the low-temperature glass-like excitations that are found in these systems.

Using Raman spectroscopy, we have measured the A1(TO) and E(TO) phonons in the tungsten bronze structured ferroelectric Ba0.4Sr0.6Nb2O6 (BSN). We observe phonon anomalies associated with Tc and also with a temperature≈ 425°C. The latter is in the region where index of refraction measurements indicate the onset of a local polarization. By quenching the crystal from high temperatures, Tc can be shifted. We find that the phonon anomalies shift corresponding to the new Tc values.

From Raman measurements on superconducting and non-superconducting YBa2Cu3O7-δ single crystals, we show that close to room temperature there is an unaccounted for, intense, oxygen vibrational mode at 598 cm−1. This (zz) polarized mode appears to arise from some chain oxygen atoms occupying another site in the crystal. Using laser heating and a shutter, we find that the time it takes to occupy or empty this site is less than 0.1 sec. If a charge carrier in the Cu-O plane induces the occupation of this new site, then a large electron-phonon coupling constant could result.

${\mathrm{La}}_{2}$${\mathrm{NiO}}_{4+\ensuremath{\delta}}$ (\ensuremath{\delta}=0) has a high-temperature tetragonal (HTT) phase (T>680 K), a low-temperature orthorhombic (LTO) phase, and a low-temperature tetragonal (LTT) phase (T70 K); that is, HTT\ensuremath{\rightarrow}LTO\ensuremath{\rightarrow}LTT). These phases are isomorphic to those of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ (x=0.12). Using Raman spectroscopy, we have measured the c-axis-polarized phonons. The $^{2}$${\mathit{A}}_{1\mathit{g}}$ modes of the HTT phase occur in all three phases at 155 and 445 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, with energies and widths only weakly dependent on temperature. The low-energy ${\mathrm{NiO}}_{6}$-octahedra tilting modes (which drive the phase transitions) have been observed and clearly show the first-order nature of the LTO\ensuremath{\rightarrow}LTT phase transition. The lowest-energy Raman mode observed (at 70 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ with ${\mathit{B}}_{1\mathit{g}}$ symmetry), allowed only in the LTT phase, involves rocking motion of the undisplaced in-plane oxygen atoms.