0000000000147123
AUTHOR
R. Feile
showing 16 related works from this author
Frequency Dependence of the Orientational Freezing in(KBr)1−x(KCN)x
1982
Dielectric, ultrasonic, and neutron-scattering measurements in ${(\mathrm{KBr})}_{1\ensuremath{-}x}{(\mathrm{KCN})}_{x}$ are reported for concentrations $x$ ranging from 0.01 to 0.5. The dipolar and the quadrupolar susceptibilities exhibit frequency- and concentration-dependent cusps showing that the freezing process into an orientational glass state is a relaxational phenomenon.
Phase transformation in a glass-ceramic observed by laser spectroscopy
1988
The influence of thermal treatment on a (Li2O∶Al2O3∶ SiO2) glass ceramic is studied by laser spectroscopy. At temperatures above 800 °C a fluorescence of Cr3+ ions around 693 nm appears which indicates the growth of crystallites where the Cr3+ ions occupy sites similar to those in Al2O3.
Intensity of theB1gphonon Raman scattering inYBa2Cu3O7: Comparison of normal and superconducting states
1995
We compare theoretically the intensity of the ${\mathit{B}}_{1\mathit{g}}$ phonon Raman scattering in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ above and below the superconducting transition temperature ${\mathit{T}}_{\mathit{c}}$. Our analysis shows that a considerable enhancement of the scattering intensity in the superconducting state that is observed experimentally can be caused by an extension of the number of intermediate electronic states near the Fermi surface that participate in the Raman process.
Anomalous thermoelastic behavior of (KI)1-x(NH4I)x
1990
Abstract An anomalous softening of the shear mode c 44 is observed in (KI) 1- x (NH 4 I) x with Brillouin scattering (10 K ⩽ T ⩽ 300 K ). It is caused by the weak quadrupolar moment of the NH 4 + ion, induced by the C 3 v symmetry of the potential. A parallel decrease of the lifetime of this transverse phonon at lower temperatures is observed. Static random strain fields due to admixing KI with NH 4 I are small. The results have been treated in terms of a mean field theory. The c 11 elastic constant does not show any anomalous behavior. Also are given the elastic constants c 11 and c 44 for x =0.14, 0.43 and 1 and 1 at T = 300 K and 10 K .
A neutron scattering study of the magnetic properties of PrSn3
1988
The intermetallic compound PrSn3 has been studied by elastic and inelastic neutron scattering. The paramagnetic phase shows overdamped crystal field excitations and an anisotropic distribution of the diffuse magnetic intensity. The dispersion relation of the excitations of the antiferromagnetic phase has been determined. The results are analyzed in terms of an anisotropic exchange coupling.
Investigations of TiO2 films deposited by different techniques
1991
High refractive TiO2 films deposited by reactive electron beam evaporation, reactive ion plating and dip coating have been characterized by optical spectroscopy, electron spectroscopy for chemical analysis, Rutherford backscattering spectroscopy, nuclear reaction analysis and Raman spectroscopy. The spectral refractive index n exhibits a strong dependence on the deposition conditions. These findings will be connected to variations in density, stoichiometry, hydrogen content (H2O) and binding structure of the layers. A strong correlation is found between optical quantities and microscopic properties of TiO2 films.
Orientational glass behaviour of K Br0.96(CN)0.04
1981
Ultrasonic measurements on the mixed crystal K Br0.96(CN)0.04 show a minimum of most of the elastic constants at 16 K. In addition we determinedc11(T) at 10 MHz and at 50 MHz observing dispersion effects. These results and previous Brillouin and neutron scattering results of other authors on higher CN-concentrations are interpreted by an orientational glass behaviour. A semiquantitative description is given in terms of the mean random field approximation.
Phonon Softening and Electron-Phonon Interaction in YBa2Cu3O7−δ
1993
We report on the Raman scattering investigation of the 335 cm−1 phonon of Ag (pseudo-B1g) symmetry in thin YBa2Cu3O7−δfilms on various substrates. The experiments yield values for the phonon softening below Tc, which differ from sample to sample. We find a linear relation between the softening and the inverse asymmetry parameter of the phonon Fano-like lineshape, when these parameters, obtained from different samples, are compared with each other. In contrast to this, the onset temperatures for the softening are the same for these samples.
Coupled rotational and translational modes in the mixed molecular crystal KBr1?x (CN) x
1980
TheE g andT 2g acoustic phonon modes of the molecular crystals KBr0.96(CN)0.04 and KBr0.86(CN)0.14 have been investigated by inelastic neutron scattering at 6, 90 and 300 K. Clear resonances due to mode-mode coupling to molecular excitations were observed. In complementary ultrasonic experiments the elastic constants were found to pass through minima as a function of temperature. The results were quantitavely explained by a model which assumes simple forms of the molecular excitation spectrum. An alternative interpretation, though being only qualitative, postulates a freezing of the CN molecules into a glass-like phase.
Charge transfer in high-Tc(Y/Pr)Ba2Cu3O7superlattices
1996
We comment on the charge-transfer model for the unique softening of the apex [O(4)] oxygen observed in Raman spectra of a- and c-oriented (${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{\mathit{m}}$(${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{\mathit{n}}$ superlattices presented in a recent paper by Ham et al. [Phys. Rev. B 50, 16 598 (1994)]. We find the size of the charge transfer necessary for the observed shift too large to explain the observations. In addition, a conclusion about the unique behavior of both types of superlattices can only be drawn if the sample quality is properly considered. \textcopyright{} 1996 The American Physical Society.
Compaction of tungsten oxide films by ion-beam irradiation
1993
Abstract Evaporated amorphous tungsten oxide films with low densities, deposited on different substrates, have been irradiated with various types of ions of different energies up to 30 MeV, and with fluences up to 10 18 cm −2 . Compaction of the films up to nearly the bulk density was observed. No changes of the stoichiometry as determined by various ion-beam analysis techniques were detectable. Raman measurements showed that ion-beam-modified films are also amorphous, but have a different microstructure from as-deposited films. The irradiated films have a higher refractive index than the as-deposited films. A low threshold for the compaction effect of a few times 10 12 ions cm −2 was found…
An interface effect in c-oriented (Y/Pr)Ba2Cu3O7 Superlattices: Raman scattering by ‘Forbidden’ phonons
1997
Abstract Raman results of ultrathin layer high Tc superlattices ( Y m Pr 1 )Ba2Cu3O7 (m = 2, 3, 4) exhibit a common feature: new peaks, absent in the bulk compounds. These peaks are attributed to oxygen B1u symmetry modes confined in the YBa2Cu3O7 layers. To explain their Raman activity a mechanism based on the asymmetry of crystal field at Y-Pr layer interfaces is proposed.
Inelastic neutron scattering study of the rotational excitations in(KBr)1−x(KCN)xin the paraelastic and structural glass state
1984
The coupled rotational-translational excitations in ${(\mathrm{KBr})}_{1\ensuremath{-}x}{(\mathrm{KCN})}_{x}$ were studied by inelastic neutron scattering for concentrations $0.008\ensuremath{\le}x\ensuremath{\le}0.20$. We followed the ${A}_{1g}\ensuremath{-}{T}_{2g}$ tunneling transition and the ${A}_{1g}\ensuremath{-}{E}_{g}$ librational excitation through the transition from the paraelastic to the structural glass state. We found that these two excitations and their coupling to the lattice strains exhibit a very different temperature dependence in the glass state. While the tunneling transition, which triggers reorientations of the ${\mathrm{CN}}^{\ensuremath{-}}$ ions, shows a drastic r…
High-pressure Raman scattering of the stretching mode in nitrogen along the 300-K isotherm
1996
We present Raman scattering studies of the vibrational band of nitrogen at room temperature between 1 and 31 GPa allowing a detailed line-shape analysis. For the fluid and \ensuremath{\beta} phases the vibrational linewidths compare to dephasing rates ${\mathit{T}}_{2}^{\mathrm{\ensuremath{-}}1}$ determined by experiments in the time domain. The \ensuremath{\delta}-\ensuremath{\epsilon} transition is unmistakably marked by a drop of the vibrational linewidths around 17 GPa. A further transition into the \ensuremath{\eta} phase around 20 GPa proposed from previous Raman results can be ruled out. Additionally, clear evidence is found for a dynamical freezing of the ${\mathrm{N}}_{2}$ molecule…
High-pressure Raman study of theN2stretching vibration in argon-nitrogen mixtures at room temperature
1996
We present room-temperature Raman investigations of the nitrogen molecule stretching vibration in ${\mathrm{Ar}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$(${\mathrm{N}}_{2}$${)}_{\mathit{x}}$ from x=1 to x=0.59 in the pressure range 1\ensuremath{\le}p\ensuremath{\le}31 GPa. Ar substitution leads to an inhomogeneous broadening of the vibrational signal. The \ensuremath{\beta}-\ensuremath{\delta} phase transition of pure ${\mathrm{N}}_{2}$ is shifted to higher pressures for x=0.75. The substituted Ar atoms preferentially occupy the 2a sites of the cubic elementary cell of the orientationally disordered \ensuremath{\delta} phase. This interpretation of the experimental data is supported by our mod…
Confined and extended optical phonons in an ultrathin-layerYBa2Cu3O7/PrBa2Cu3O7superlattice
1995
Raman-scattering studies of a high-quality ultrathin-layer (${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{4}$/(${\mathrm{PrBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$${)}_{1}$ superconducting superlattice resolve, in addition to the combined ${\mathit{B}}_{1\mathit{u}}$ mode at 310 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ previously reported for a 2:1 sample, a peak at 350 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ at low temperature. This peak and also others have been interpreted by a lattice-dynamical calculation for the superlattice. The results are compared with confined or extended phonon pictures. The superlattice mode is not renormalized below the superconducti…