Evaluation of Raman Scattering in La1-xMxMnO3 Single Crystals Due to Structural and Magnetic Transitions

1997 ◽  
Vol 494 ◽  
Author(s):  
V. B. Podobedovm ◽  
A. Weber ◽  
D. B. Romero ◽  
J. P. Rice ◽  
H. D. Drew
Keyword(s):  
Raman Scattering ◽  
Single Crystals ◽  
Raman Spectra ◽  
Phonon Scattering ◽  
Strong Dependence ◽  
Low Frequency ◽  
Anomalous Behavior ◽  
Magnetic Phase Transitions ◽  
Raman Mode ◽  
Jahn Teller

ABSTRACTThe study of doped and undoped La1-xMxMnO3 single crystals (x = 0 to x = 0.3) in the temperature range from 5 K to 423 K is reported. The activity of phonon vibrational modes in optical spectra is analyzed and a comparison to experimental Raman data is presented. Different contributions from optical phonons to the Raman scattering process are discussed. It is shown that both the value of doping and temperature have a significant influence on Raman features, and these are strongly affected by structural and magnetic phase transitions. Due to the symmetry present in distorted lanthanum manganese compounds their Raman spectra were found to contain comparable contributions from first- and second-order phonon scattering. The common features related to both the reduction of the Jahn-Teller (JT) distortion and the temperature-induced phase transition were found in the Raman spectra of La1-xMxMnO3 crystals. An anomalous behavior of the low-frequency Raman mode in doped systems was found and explained in terms of the temperature-dependent ionic radius of the La/Sr ion sites. It was found that the strong dependence of the Ag Raman mode on the value of doping may serve as a useful tool for optical characterization of La1-xMxMnO3 compounds, including the inhomogeneity of the surface.

Low frequency Raman spectra of the liquid and plastic crystal phases of O2, N2, CO, and of Ar crystals with these molecules as guests

1982 ◽  
Vol 60 (9) ◽  
pp. 1358-1364 ◽  
Author(s):  
N. H. Rich ◽  
M. J. Clouter ◽  
H. Kiefte ◽  
S. F. Ahmad
Keyword(s):  
Single Crystals ◽  
Raman Spectra ◽  
Phonon Mode ◽  
Low Frequency ◽  
Impurity Molecule ◽  
Spectral Features ◽  
Background Impurity ◽  
Crystal Phases ◽  
Distinct Features ◽  
Frequency Feature

Low frequency Raman spectra of single crystals of orientationally disordered phases of oxygen, nitrogen, and carbon monoxide, and spectra of those substances as liquids show two linear segments in semi-log plots. Slopes of the higher frequency segments are nearly equal for all cases; slopes of the lower frequency segments are particular to the substance and are nearly the same in both liquid and crystal for O2 and CO. Spectra of single crystals of argon doped with O2, N2, or CO show two distinct features superimposed on a sloping background. Impurity molecule reorientation apparently accounts satisfactorily for all spectral features, but translation–rotation coupling may allow a contribution to the higher frequency feature arising from a local phonon mode in argon.

scholarly journals Terahertz Time-Domain Spectroscopy and Low-Frequency Raman Scattering of Crystalline and Glassy Pharmaceutical Indapamide

2015 ◽  
Vol 46 ◽  
pp. 16-22 ◽  
Author(s):  
Yukiko Kobayashi ◽  
Tomohiko Shibata ◽  
Tatsuya Mori ◽  
Seiji Kojima
Keyword(s):  
Raman Scattering ◽  
Raman Spectra ◽  
Imaginary Part ◽  
Time Domain ◽  
Low Frequency ◽  
Dielectric Constants ◽  
Coupling Constants ◽  
Exclusion Principle ◽  
Terahertz Time Domain Spectroscopy ◽  
Time Domain Spectroscopy

We performed terahertz time-domain spectroscopy and low-frequency Raman scattering on crystalline and glassy states of pharmaceutical indapamide (IND). We have determined the real and imaginary part of the complex dielectric constants and the imaginary part of the Raman susceptibility in the THz region. Several phonon peaks have been observed in the crystalline IND and the mutual exclusion principle of infrared and Raman spectroscopy holds in the measured frequency range. In a glassy state of IND, a broad absorption peak has been observed in both the THz and the Raman spectra with different spectral shape, and this disagreement indicates that the far-infrared and Raman light-vibration coupling constants are different in the glassy IND. A clear boson peak has been observed in the Raman spectra of the glassy IND at about 0.5 THz.

Polarized Raman Scattering Study of ZnGeP2 Single Crystals

1997 ◽  
Vol 484 ◽  
Author(s):  
Spirit Tlali ◽  
Howard E. Jackson ◽  
M. C. Ohmer ◽  
P. G. Schunemann ◽  
T. M. Pollak
Keyword(s):  
Raman Scattering ◽  
Single Crystals ◽  
Raman Spectra ◽  
Low Temperatures ◽  
High Quality ◽  
Crystal Orientations ◽  
Gradient Technique ◽  
Theoretical Predictions ◽  
Scattering Study ◽  
Polarized Raman

AbstractRaman scattering experiments on high quality ZnGeP2 single crystals grown by the seeded horizontal dynamic gradient technique have been carried out. Polarized Raman spectra were obtained in the backscattering geometry at both room and low temperatures for several crystal orientations and compared with group theoretical predictions. Raman spectra from as-grown and annealed samples display distinctive differences which were explored by utilizing two different excitation wavelengths: 514.3 nm and 632.8 nm; the observed differences are attributed to a surface interdiffuasion effect.

Raman scattering and theoretical studies of Jahn—Teller induced phase transitions in some rare-earth compounds

1972 ◽  
Vol 328 (1573) ◽  
pp. 217-266 ◽  
Keyword(s):  
Rare Earth ◽  
Phase Transitions ◽  
Raman Scattering ◽  
Raman Spectra ◽  
Mode Coupling ◽  
Equations Of Motion ◽  
Structural Phase ◽  
Phase Changes ◽  
Phonon Modes ◽  
Jahn Teller

The rare-earth crystals DyVO 4 , DyAsO 4 and TbVO 4 undergo structural phase transitions at 14, 12 and 34 K respectively induced by a cooperative Jahn-Teller effect. An experimental investigation of the phase changes has been made using Raman scattering methods. For purposes of comparison, the Raman spectra of DyPO 4 , YVO 4 and GdVO 4 (which do not undergo phase transitions) have also been measured. A detailed theory of the phase transitions has been developed which accounts for the electronic and vibrational Raman spectra. The lowest four electronic levels of Dy 3+ and Tb 3+ are treated in a pseudospin formalism, and the theory is discussed in terms of mixed phonon and pseudo-spin excitations. The singly degenerate κ ≈ 0 optic phonons are not measurably affected by the transitions, but splittings of up to 20 cm -1 developed in the doubly degenerate E g phonon modes in the Raman spectra owing to anharmonic couplings with the electronic states. Splittings are also observed in the lowest electronic levels of the rate earth ions below the transition temperature; these electronic modes effectively constitute the soft mode which causes the transitions to occur. A molecular field model is first used in the theoretical analysis. The equations of motion of the coupled excitations are then found and the energies, line widths and dispersion of the mixed excitations are discussed. The connexion between the static strain and the acoustic phonon mode coupling is investigated, and a thermodynamic treatment of the elastic constants is given. From the Raman data, it appears that in TbVO 4 the acoustic mode coupling is stronger than the optic mode coupling.

RESONANCE BAND IN Ge/Si SUPERLATTICE STUDIED BY RAMAN SCATTERING

2003 ◽  
Vol 02 (04n05) ◽  
pp. 363-368
Author(s):  
C. H. LIN ◽  
B. CHEN ◽  
C. T. CHIA ◽  
H. H. CHENG
Keyword(s):  
Raman Scattering ◽  
Raman Spectra ◽  
Low Frequency ◽  
Interface Layer ◽  
Laser Line ◽  
Continuous Emission ◽  
Diode Pump ◽  
Resonance Band ◽  
Raman Measurement ◽  
532 Nm

We have performed the low-frequency Raman measurement of MBE grown Ge/Si superlattice. Raman spectra were excited by He–Ne laser, and diode-pump YAG 532 nm laser, as well as several lines from Ar+ laser. Folded acoustic phonons of the Ge/Si superlattice were clearly found. The resonant effects were observed for the Ge/Si superlattices while the Raman spectra excited by the laser lines around 500 nm. A clearly resonance enhanced phonon signals are found for the spectrum excited by 532 nm laser line, and continuous emission can be clearly seen. By the continuous emission theory, we carried out a resonance band at 2.32 eV, which is closed to the E1 band of Germanium. Few weak resonant bands were also found near 2.32 eV, which may be related to confined band or the resonance band of interface layer between Si and Ge .

scholarly journals Raman Scattering in Cuprate Superconductors

1997 ◽  
Vol 11 (18) ◽  
pp. 2093-2118 ◽  
Author(s):  
Thomas Peter Devereaux ◽  
Arno Paul Kampf
Keyword(s):  
Low Temperature ◽  
Raman Scattering ◽  
Raman Spectra ◽  
Cuprate Superconductors ◽  
Energy Gap ◽  
Low Frequency ◽  
Temperature Behavior ◽  
Doping Dependence ◽  
Electronic Raman Scattering ◽  
Effects Of Disorder

A theory for electronic Raman scattering in the cuprate superconductors is presented with a specific emphasis on the polarization dependence of the spectra which can infer the symmetry of the energy gap. Signatures of the effects of disorder on the low frequency and low temperature behavior of the Raman spectra for different symmetry channels provide detailed information about the magnitude and the phase of the energy gap. Properties of the theory for finite T will be discussed and compared to recent data concerning the doping dependence of the Raman spectra in cuprate superconductors, and remaining questions will be addressed.

A Study of the Temperature-Dependence of Low-Frequency, Raman-Active Phonons in Stage-2 Graphite-K and Graphite-Rb Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
J. Giergiel ◽  
P. C. Eklund ◽  
R. Al-Jishi ◽  
G. Dresselhaus
Keyword(s):  
Phase Transitions ◽  
Raman Scattering ◽  
Temperature Dependence ◽  
Raman Spectra ◽  
Lattice Dynamics ◽  
Low Frequency ◽  
Frequency Region ◽  
Intercalation Compounds ◽  
Dynamics Model ◽  
Scattering Study

ABSTRACTWe report results from a Raman scattering study of stage 2 Graphite-Rb and Graphite-K in the low frequency region (ω < 150 cm-1) as a function of temperature (80K < T < 300K). Four features are seen in the 80K spectra and are interpreted in terms of a Born– von Kármán lattice dynamics model. The temperature-dependence of the Raman spectra is discussed in connection with reported phase transitions in stage 2 alkalimetal graphite compounds.

Vibrational Raman Scattering from high TC single Crystals

1987 ◽  
Vol 99 ◽  
Author(s):  
D. M. Krol ◽  
M. Stavola ◽  
L. F. Schneemeyer ◽  
J. V. Waszczak ◽  
W. Weber
Keyword(s):  
Chemical Composition ◽  
Raman Scattering ◽  
Single Crystals ◽  
Raman Spectra ◽  
Peak Position ◽  
High Tc ◽  
Stretching Vibration ◽  
Polarized Raman ◽  
Axial Stretching

ABSTRACTPolarized Raman spectra have been measured on single crystals of the high Tc materials A2BCu3Ox with A=Ba and Sr, B=Y and La and 6<x<7. The dependence of the 500 cm-i peak position (αzz)on chemical composition is in agreement with its assignment to the O(1) axial stretching vibration. The intensity of the 600 cm1 band, which has been ascribed to a defect induced Cu-O mode, strongly depends on the crystal preparation and resulting purity.

Raman Investigation of the Layered Manganese Perovskite La1.2Sr1.8Mn2O7

1997 ◽  
Vol 494 ◽  
Author(s):  
D. B. Romero ◽  
V. B. Podobedov ◽  
A. Weber ◽  
J. P. Rice ◽  
J. F. Mitchell ◽  
...  
Keyword(s):  
Critical Temperature ◽  
Raman Scattering ◽  
Temperature Dependence ◽  
Raman Spectra ◽  
Anomalous Behavior ◽  
Spectral Features ◽  
Long Wavelength ◽  
Manganese Perovskite

ABSTRACTWe report the results of a detailed polarization and temperature dependence study of the Raman scattering from La1.2Sr1.8Mn2O7. The Raman spectra reveal three general spectral features. First, there are sharp peaks due to long-wavelength optic phonons. Phonons, attributed to the distortion of the MnO6 octahedra, reveal an anomalous behavior which correlates with the transition from a paramagnetic-insulating (PI) to a ferromagnetic-metallic (FM) phase at a critical temperature Tc. Second, there is an electronic continuum that is suppressed for ω < 500 cm−1 at T ≪ Tc. Third, broad peaks between 400 cm1 to 800 cm−1 seen in the PI state, surprisingly, disappear in the FM state. The implications of these results are discussed.

scholarly journals Запрещенное резонансное комбинационное рассеяние света в сверхрешетках GaAs/AlAs: эксперимент и расчеты

2018 ◽  
Vol 52 (6) ◽  
pp. 569
Author(s):  
В.А. Володин ◽  
В.А. Сачков ◽  
М.П. Синюков
Keyword(s):  
Dipole Moment ◽  
Raman Scattering ◽  
Raman Spectra ◽  
Wave Vector ◽  
Phonon Scattering ◽  
Optical Microscope ◽  
Deformation Potential ◽  
Potential Mechanism ◽  
Model Approximation ◽  
Born Model

AbstractThe Raman spectra of GaAs/AlAs(100) superlattices are calculated and studied experimentally for various wave-vector directions. The experiments are performed when applying a confocal optical microscope combined with a micro-Raman spectrometer for various scattering geometries both for phonons with a wave vector directed along the normal to a superlattice and in the in-plane geometry. The frequencies and eigenvectors of phonons are calculated in the extended Born model approximation taking into account Coulomb interaction in the rigid-ion approximation. The Raman spectra are calculated in the scope of the deformation- potential mechanism; herewith, it turns out that additional peaks, which are not described in the scope of this approach, appear in the experimental spectra. It seems likely that these peaks appear due to the manifestation of Raman scattering forbidden by selection rules under resonance conditions. An attempt is made to explain the appearance of these peaks in the experimental spectra within the scope of inelastic phonon scattering at bound charges (phonons with a large dipole moment).

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