共查询到20条相似文献,搜索用时 15 毫秒
1.
E.S. Clementyev K. Conder A. Furrer I.L. Sashin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):465-467
We provide here experimental data on the phonon density-of-states of MgB2 obtained by the inelastic neutron scattering technique. The measurements were performed for the natural boron-based magnesium
diboride with use of a time-of-flight neutron spectrometer. Several phonon bands were observed in the phonon spectrum at energies
of about 33, 55, 82 and 99 meV. We show that the cut-off energy of the density-of-states occurs at around 105 meV which is
much higher than expected so far from heat-capacity data and partially explains the high T
c
value observed for MgB2. The characteristic phonon energies are indicative of an intermediate coupling regime in this compound. We conclude that
a much needed neutron experiment aimed at the study of the isotopic effect in the phonon density-of-states of MgB2 is conceivable.
Received 19 March 2001 相似文献
2.
The photoluminescence spectrum of Si:In measured at 2 and 4 K using samples from several suppliers has been found to be preparation sensitive. In particular, intensity variations allow us to distinguish a sharp no-phonon line at 1.118 eV, variously referred to as U2 of P, and its associated vibronic spectrum from the In(NP) lines and their phonon replicas. Whereas the intensity of the latter did not show preparation sensitivity, the former has been observed to change by three orders of magnitude. The U2 vibronics form a broad-structured spectrum containing density-of-states features. The appearance of phonons other than those conserving crystal momentum demonstrates the exciton is bound to a low symmetry site. In addition, the spectrum includes a peak at 1.109 eV, called R, and a shoulder at 1.107 eV which involves too small an energy loss to be density-of-states related, and these features are most likely modes of the U2 impurity complex. This complex has been tentatively identified as an isoelectronic center composed of an indium-phosphorus nearest-neighbor substitutional pair. 相似文献
3.
Yi Wang Huazhi Fang Chelsey L. Zacherl Zhigang Mei Shunli Shang Long-Qing Chen Paul D. Jablonski Zi-Kui Liu 《Surface science》2012,606(17-18):1422-1425
We present the calculation of the lattice dynamics of chromia (Cr2O3), a typical Mott–Hubbard insulator, employing the first-principles density functional theory plus U approach. We first report the phonon dispersions at the theoretical equilibrium volume. Then the phonon density-of-states is calculated as a function of volume. Finally, the atomic volume, heat capacity, linear thermal expansion coefficient, bulk modulus, Grüneisen constant, and elastic constants are calculated as functions of temperature. 相似文献
4.
A weighted phonon frequency distribution has been measured in PbF2 at temperatures 10, 302, 660 and 910 K, using a neutron scattering technique. At 10 K good agreement is found between the measured distribution and the phonon density-of-states calculated from the low temperature dispersion relation of PbF2. At the higher temperatures, near the ionic conductivity transition temperature, Tc ~ 700 K, the optic modes are observed to broaden into a high energy tail consistent with strong anharmonicity or extensive disorder. A low energy peak arising from transverse acoustic modes remains well defined even at temperatures above Tc. 相似文献
5.
A review is given on recent high-pressure experiments using nuclear resonant scattering of synchrotron radiation. We shortly
introduce the methodological aspects connected with high-pressure experiments applying nuclear forward scattering and nuclear
inelastic scattering of synchrotron radiation. Selected examples for the study of magnetism are given for the Laves phases
LuFe2 and ScFe2, where we studied the variation of the magnetic ordering temperature and of the Fe band moment as a function of pressure.
An actual example for the study of lattice dynamics is a recent investigation of the phonon density-of-states in metallic
iron with special emphasis on hcp ε-Fe, where the pressure-induced texture is used, in conjunction with theoretical calculations,
to extract density of phonon states as seen parallel and perpendicular to the hexagonal c-axis.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Results of ir and Raman investigations on trigonal layer-structured Si2Te3 single crystals are reported. The ir reflection spectrum withEc exhibits seven reststrahl-like bands, whereas the corresponding spectrum withEc shows only one very small bump. Values for
0 and
are given. The Raman spectra are very rich in structure and can only be interpreted qualitatively as being a mixture of single phonon lines and one- and two-phonon density-of-states contributions. One-phonon density-of-states effects are disorder-induced owing to the statistical occurrence of the Si atoms within the regular hexagonal Te sublattice. 相似文献
7.
Hui Wang Xuewei Cao Min Feng Qinghua Jin Datong Ding Guoxiang Lan 《Journal of Physics and Chemistry of Solids》2009,70(1):8-14
The phonon dispersions of single-wall BC3 nanotubes with any chirality are calculated within a symmetry-based force constant model of the lattice dynamics. Based on the non-symmorphic symmetry group of the BC3 tubes, the symmetries and number of the Raman- and infrared-active modes at Γ point of the one-dimensional Brillouin zone are given. The neighbor atom-atomic interaction force constants are recalculated by fitting them to the experimental phonon energy-dispersion curves of honeycomb BC3 sheet. The frequencies of the optically active modes are presented as the function of diameters and chiralities for BC3 tubes. The obtained phonon density-of-states spectra, phonon dispersion relations, and vibrational patterns of the zone-center phonons are presented and discussed in detail. The calculated frequencies of infrared-active modes are compared with the experimental values reported in the literature. The results provide comprehensive information about the vibrational properties of the BC3 tubes and shed light on the interpretation of Raman scattering and infrared spectroscopies. 相似文献
8.
《Solid State Communications》1987,63(2):163-166
The Raman spectra and reflectivity of r.f. sputtered amorphous semimetallic a-NiSi2 and a-CrSi2 thin films are reported. Substantial differences between the two amorphous disilicide Raman spectra are associated with changes in the phonon density-of-states as a result of variations in Si(p)-transition metal (d) interactions. The greater width of the bands in the Cr alloy suggests a less ordered local environment. Neither spectrum indicates distinct a-Si-like bands, demonstrating that significant short range order changes have occured. 相似文献
9.
A. Junod P. Bellon R. Flükiger F. Heiniger J. Muller 《Zeitschrift für Physik B Condensed Matter》1972,15(2):133-141
Specific heat measurements from1 to 40 K give some insight into the phonon spectrum of the alloy V3Au. The minute differences between the as-cast and annealed states indicate that the drastic change of the superconducting transition temperature upon ordering is not likely to be of phononic origin. Alternatively, this behaviour can be understood as a consequence of an electronic density-of-states change in the presence of a large Coulomb pseudopotential term. This assumption is supported by susceptibility measurements. 相似文献
10.
Using first principles density functional theory, we predict a monolayer B2Si structure with space group Pmm2 in the present work. This structure is confirmed to be dynamically stable. Based on the plane wave pseudopotential approach, the charge density, electron localization function, density of states, energy band, phonon property and thermal conductivity of Pmm2-B2Si are systematically studied. It is interesting that the sp2 hybridization and coordination bond of Si are found in Pmm2-B2Si, which is the most important factor for its structural stability. The density of states and energy band analysis reveals that Pmm2-B2Si is metallic because of the partial occupied Si 3pz and B 2pz states. Moreover, the acoustic-optical coupling is important for phonon transport in Pmm2-B2Si, and the contribution of optical modes to the lattice thermal conductivity along the [100] and [010] directions is 13% and 12%, respectively. This study gives a fundamental understanding of the structural, electronic and phonon properties in Pmm2-B2Si. 相似文献
11.
V.?Yu.?Tarenkov A.?I.?D’yachenko S.?L.?Sidorov V.?A.?Bo?chenko D.?I.?Bo?chenko ?.?Chromik V.??trbík ?.?Ga?i M.??panková ?.?Beňa?ka 《Physics of the Solid State》2009,51(9):1778-1784
The specific features of the phonon spectrum of the MgB2 compound (T
c
= 38 K) are investigated by tunneling spectroscopy. It is demonstrated that both the position and the energy width of the
fundamental optical mode E
2g
in the phonon spectrum are in good agreement with inelastic X-ray spectroscopy data but differ substantially from Raman spectroscopy
results. Among possible factors responsible for this discrepancy, the anharmonic and nonadiabatic effects that are characteristic
of the MgB2 system are discussed. 相似文献
12.
The problem of complex Fermi resonance (FR) involving a local vibration is considered. It is shown for the first time that in the PbI2 crystal, owing to the features of phonon bands, the following two effects superpose on each other: (1) the traditional FR between the fundamental Ω(A1g) vibration and the two‐phonon states (TPS) arising from the 2Ω(Eu) vibrations, and (2) the FR between the impurity vibration and the same TPS band. It is shown theoretically that in the case of such complex FR the shape of the spectrum strongly depends on the impurity concentration, anharmonic constants and the phonon band structure. An analysis of experimental data and comparison with theory is made. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
13.
The far-infrared optical reflectivity of an optimally doped Ba1-xKxFe2As2(x =0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1 . This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound. 相似文献
14.
The lattice dynamical property of AuCuZn2 has been investigated by means of inelastic neutron scattering technique in connection with its martensitic phase transformation. The temperature dependent soft phonon was observed transformation. The temperature dependent soft phonon was observed around of TA2 phonon branch. We have also found a premartensitic metastable phase, in which new satellite reflections at (H± , K ? , 0) have been observed around fundamental reflections with H + K = 4n. The atomic displacements of the soft phonon mode correspond to the atomic arrangement of the premartensitic phase. 相似文献
15.
First-principles calculations of the band structure for Hg3Se2Cl2 crystal were performed by means of density functional theory (DFT). The exchange and correlation potential was described within a framework of the local density approximation based on exchange-correlation energy optimization to calculate the total energy. DOS/PDOS and valence charge distribution were studied in details. Absorption near the fundamental edge was found to be due to indirect and direct allowed transitions. For device applications based on Hg3Se2Cl2 crystal, understanding these fundamental issues is highly important and essential. It should be noted that optoelectronic applications of Hg3Se2Cl2 are caused by coexistence of the large polarized Hg cations and a huge contribution of an harmonic phonon subsystem caused by anions. 相似文献
16.
I. A. Damaskin S. L. Pyshkin S. I. Radautsan V. E. Tazlavan 《Optical and Quantum Electronics》1973,5(5):405-410
A study has been made of photoconductivity in Cdln2S4 induced by 1.17 eV photons from a Q-switched neodymium laser. Both three-photon absorption, and two-photon absorption involving the emission of a phonon, have been investigated. The experimental data are in satisfactory agreement with the theory of multi-quantum transitions which takes into account the peculiarities of crystal zone structure.The investigation of competing multi-quantum transitions is a new method which permits one to obtain information on the fundamental optical constants of solids. 相似文献
17.
B. Renker F. Gompf E. Gering G. Roth W. Reichardt D. Ewert H. Rietschel H. Mutka 《Zeitschrift für Physik B Condensed Matter》1988,71(4):437-442
From inelastic neutron scattering experiments, we determined the generalized phonon density-of-states (PDOS) for the high-T
c
superconductors MEBA2Cu3O7 (ME=Y, Y0.5Pr0.5, Nd) and the non-superconducting references YBa2Cu3O6 and PrBa2Cu3O7. A detailed study of the Y-O7 compound at temperatures between 300 K and 6 K gave no evidence of any pronounced soft-mode behaviour. Moderate changes only occur in the PDOS between Nd and Pr samples and Y and Y0.5Pr0.5 samples, respectively, but drastic differences show up in the Y-O7 and Y-O6 spectra. Thus, we could not find correlations betweenT
c
-values and particular features in the PDOS although there is some evidence that electron-phonon coupling is strong in this class of materials. 相似文献
18.
Surajit Saha Sudakshina Prusty Surjeet Singh R. Suryanarayanan A. Revcolevschi A. K. Sood 《Journal of Raman spectroscopy : JRS》2012,43(4):549-555
Anomalous temperature dependence of Raman phonon wavenumbers attributed to phonon–phonon anharmonic interactions has been studied in two different families of pyrochlore titanates. We bring out the role of the ionic size of titanium and the inherent vacancies of pyrochlore in these anomalies by studying the effect of replacement of Ti4 + by Zr4 + in Sm2Ti2O7 and by stuffing Ho3 + in place of Ti4 + in Ho2Ti2O7 with appropriate oxygen stoichiometry. Our results show that an increase in the concentration of the larger ion, i.e. Zr4 + or Ho3 +, reduces the phonon anomalies, thus implying a decrease in the phonon–phonon anharmonic interactions. In addition, we find signatures of coupling between a phonon and crystal field transition in Sm2Ti2O7, manifested as an unusual increase in the phonon intensity with increasing temperature. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
20.
Density-functional perturbation theory has been applied to investigate the thermodynamic properties of two-dimensional MoS2 within the Perdew-Burke-Ernzerhof genealized gradient approximation (PBE-GGA). The Murnaghan’s isothermal equation of state has been derived for the monolayer, giving how the pressure and the total energy of the monolayer evolve versus the volume of the unit cell. The temperature-dependent behavior of some thermodynamic quantities, including the Helmholtz free energy, total energy, Debye temperature, mean square displacements, specific heat, entropy and number of microstates, have been determined as well as their functional forms within the quasi-harmonic approximation, by calculating the partial phonon density of states as a fundamental quantity. The value of 45.6 cm has been found for the phonon band gap in the frequency range, separating the acoustic and the optical phonon bands in fair agreement with the literature. The results broadly support the view that the validity of the Debye T3-law for low-temperature specific heat of solids is violated for the case of two-dimensional MoS2 and therefore, a T2-law is proposed, accurately describing the behavior of the isochoric specific heat from 0 to 60 K. 相似文献