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1.
Inelastic neutron scattering experiments have been carried out to measure the phonon density of states in polycrystalline
α-ZnCl2 at Dhruva, Trombay. Lattice dynamical calculations, based on an interatomic potential model, are accomplished to study phonons
associated with this otherwise extremely hygroscopic compound. Our calculated data are found to be well-compatible with the
available measured ones. 相似文献
2.
《Solid State Communications》2002,121(6-7):333-338
We report coherent inelastic neutron scattering measurements of the phonon dispersion relations and lattice dynamics shell model calculations of several microscopic and macroscopic properties of andalusite, Al2SiO5. Andalusite has an orthorhombic structure with 32 atoms/unit cell. The inelastic neutron scattering measurements (up to energy transfers of 45 meV) were carried out using the triple axis spectrometer at Dhruva reactor, India using a single crystal of andalusite and the phonon dispersion relations along the [100] direction have been measured. The shell model calculations have been used to compute the crystal structure, elastic constants, phonon frequencies, dispersion relations, density of states and the specific heat. The calculated results are in good agreement with available experimental data. The computed one-phonon neutron scattering structure factors based on the shell model have been very useful in the planning and analysis of the inelastic neutron scattering experiments. 相似文献
3.
We report here measurements of the phonon density of states and the lattice dynamics calculations of strontium tungstate (SrWO4). At ambient conditions this compound crystallizes to a body-centred tetragonal unit cell (space group I41/a) called scheelite structure. We have developed transferable interatomic potentials to study the lattice dynamics of this
class of compounds. The model parameters have been fitted with respect to the experimentally available Raman and infra-red
frequencies and the equilibrium unit cell parameters. Inelastic neutron scattering measurements have been carried out in the
triple-axis spectrometer at Dhruva reactor. The measured phonon density of states is in good agreement with the theoretical
calculations, thus validating the interatomic potential developed.
相似文献
4.
NaNbO3 and (Sr,Ca)TiO3 exhibit an unusual complex sequence of temperature- and pressure-driven structural phase transitions. We have carried out
lattice dynamical studies to understand the phonon modes responsible for these phase transitions. Inelastic neutron scattering
measurements using powder samples were carried out at the Dhruva reactor, which provide the phonon density of states. Lattice
dynamical models have been developed for SrTiO3 and CaTiO3 which have been fruitfully employed to study the phonon spectra and vibrational properties of the solid solution (Sr,Ca)TiO3.
相似文献
5.
The phonon dispersion curves have been calculated from a microscopic model for Nb3Sn at 300 K and are in good agreement with the available inelastic neutron scattering data. The calculated phonon density of states exhibits the essential features of the experimental results obtained by incoherent inelastic neutron scattering. 相似文献
6.
In this paper we report the results obtained from inelastic neutron scattering measurements on Zr2NiH1.9 and Zr2NiH4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes
of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon
spectra from 35–180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we
assume a set of Ein-stein modes due to the hydrogen atoms which are delta functions in energy. These delta functions are broadened
by the resolution of the instrument. The vibrational frequencies obtained from the fitting of the observed phonon spectra
have been assigned to various tetrahedral sites in both the compounds. 相似文献
7.
氮化铀(UN)因其较好的热物性和耐事故容错性成为先进动力堆的候选燃料,但目前热能区缺少可靠的UN热中子截面数据,这对于热中子反应堆物理计算是很不利的.本文基于量子力学的第一性原理,利用VASP/PHONON软件模拟计算了UN的声子态密度,以此为积分得到UN的定容比热容,并基于新制作的声子态密度,采用核截面处理程序NJOY/LEAPR,利用热中子散射理论,得到UN的S(α,β)数据,进而研究UN的热中子散射截面,并与传统压水堆的二氧化铀(UO2)进行对比.结果表明:优化的晶格参数与数据库符合较好,UN声子态密度的声子项和光子项较UO2的分隔更加明显,定容比热容计算结果与实验值一致,基于该声子态密度计算得到的UN中238U的非弹性散射和弹性散射截面比相同温度下UO2中238U小,UN中N仅考虑了非相干散射部分,随着温度升高,UN弹性散射截面变小,非弹性散射变大,并在高能段趋于自由核散射截面.本文的研究结果填补了UN热中子截面数据的缺失,为下一步系统研究UN燃料在轻水堆中的中子学性能奠定了基础. 相似文献
8.
P.T. Jochym K. Parlinski M. Sternik 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):9-13
Ab initio calculations and a direct method have been applied to derive the phonon dispersion curves and phonon density of states for
the TiC crystal. The results are compared and found to be in a good agreement with the experimental neutron scattering data.
The force constants have been determined from the Hellmann-Feynman forces induced by atomic displacements in a supercell. The calculated phonon density of states suggests that vibrations of Ti atoms form acoustic branches, whereas the
motion of C atoms is confined to optic branches. The elastic constants have been found using the deformation method and compared
with the results obtained from acoustic phonon slopes.
Received 23 February 1998 相似文献
9.
We review current research on minerals using inelastic neutron scattering and lattice dynamics calculations. Inelastic neutron
scattering studies in combination with first principles and atomistic calculations provide a detailed understanding of the
phonon dispersion relations, density of states and their manifestations in various thermodynamic properties. The role of theoretical
lattice dynamics calculations in the planning, interpretation and analysis of neutron experiments are discussed. These studies
provide important insights in understanding various anomalous behaviour including pressure-induced amorphization, phonon and
elastic instabilities, prediction of novel high pressure phase transitions, high pressure-temperature melting, etc.
相似文献
10.
O. Delaire 《Applied Physics A: Materials Science & Processing》2010,99(3):523-529
Several recent studies of phonons combining inelastic neutron scattering and first-principles calculations are summarized. Inelastic neutron scattering was used to measure the phonon densities of states of the A15 compounds V3Si, V3Ge, and V3Co at temperatures from 10 K to 1273 K. It was found that phonons in V3Si and V3Ge, which are superconducting at low temperatures, exhibit an anomalous stiffening with increasing temperature, whereas phonons in V3Co have a normal softening behavior. Additional measurements of the phonon DOS of BCC V alloys were performed, and it was found that a stiffening anomaly present in pure V is suppressed upon introduction of extra d-electrons by alloying. First-principles calculations of the electronic and phonon densities of states show that in both these systems, the anomalous phonon stiffening originates with an adiabatic electron–phonon coupling mechanism. The anomaly is caused by the thermally-induced broadening of sharp peaks in the electronic density of states, which tends to decrease the electronic density at the Fermi level. These results illustrate how the combined use of first-principles calculations and inelastic neutron scattering provides powerful insights into couplings of excitations in condensed-matter. 相似文献
11.
P. P. Parshin M. G. Zemlyanov G. Kh. Panov A. A. Shikov A. A. Naberezhnov Yu. A. Kumzerov I. V. Golosovsky A. S. Ivanov 《Journal of Experimental and Theoretical Physics》2010,111(6):996-1002
The thermal atomic vibration spectrum of lead nanostructured in porous glass with an average pore size of 7 nm and the thermal
vibration spectrum of conventional bulk lead (taken for comparison) are measured using inelastic neutron scattering. The density
of states in the phonon spectrum of lead nanoparticles is found to exceed the density of states in the spectrum of bulk lead
at both low (E < 2.5 meV) and high (E > 9.5 meV) energies. These data are used to propose a model for the structure of a porous glass-lead nano-composite. 相似文献
12.
The phonon density of states of V3Si at 300°K has been calculated from a microscopic model. It exhibits three pronounced peaks, in qualitative agreement with experimental results of Schweiss obtained from inelastic neutron scattering. By reducing the effective charges of both ions the agreement can be improved, but at the expense of agreement for the mode softening. 相似文献
13.
R. Wiśniewski R. Dimitrova I. Natkaniec J. Wasicki 《Solid State Communications》1985,54(12):1073-1075
The results of simultaneous measurements of inelastic incoherent neutron scattering (IINS) and neutron diffraction on NiHx system with x = 0.40, 0.28 and 0.12 at temperatures of 77 K are briefly presented. In the phonon density of states, supposing a one-phonon mechanism for the scattering process, the optic modes appear as a broad band from 70 to 140 meV with a strong peak at 90 meV and weak peaks at 105 and 130 meV. Neutron diffraction confirms information about the phase composition of the samples investigated. 相似文献
14.
The phonon spectra of metallic disilicides VSi2, NbSi2, and TaSi2 have been studied in detail by inelastic neutron scattering at 300 K and specific heat measurements between 10 K and 250 K. The specific heat calculated from the generalised phonon density of states extracted from neutron measurements is in good agreement with the measured lattice contribution to the specific heat. The properties of the phonon spectra are discussed in relation with other data reported for these isostructural and isoelectronic disilicides. 相似文献
15.
Inelastic neutron scattering was used to measure the phonon densities of states of the A15 compounds V3Si, V3Ge, and V3Co at temperatures from 10 to 1,273 K. It was found that phonons in V3Si and V3Ge, which are superconducting at low temperatures, exhibit an anomalous stiffening with increasing temperature, whereas phonons in V3Co have a normal softening behavior. First-principles calculations show that this anomalous increase in phonon frequencies at high temperatures originates with an adiabatic electron-phonon coupling mechanism. The anomaly is caused by the thermally induced broadening of sharp peaks in the electronic density of states of V3Si and V3Ge, which tends to decrease the electronic density at the Fermi level. These results show that the adiabatic electron-phonon coupling can influence the phonon thermodynamics at temperatures exceeding 1,000 K. 相似文献
16.
P. S. Goyal 《Pramana》2004,63(1):15-24
Inter University Consortium for Department of Atomic Energy Facilities (IUC-DAEF) is an autonomous institute of the University
Grants Commission and provides an interface between the university fraternity and the institutions of Department of Atomic
Energy. Mumbai Centre of IUC-DAEF promotes and supports the use of neutron facilities at Dhruva reactor by the university
scientists. To augment the existing neutron scattering facilities, IUC-DAEF has developed a neutron beam line at Dhruva reactor.
The present paper gives a brief survey of the activities and achievements of Mumbai Centre of IUC-DAEF. 相似文献
17.
We investigated the structural and dynamical properties of a tetrahedrally coordinated crystalline ice from first principles based on density functional theory within the generalized gradient approximation with the projected augmented wave method. First, we report the structural behaviour of ice at finite temperatures based on the analysis of radial distribution functions obtained by molecular dynamics simulations. The results show how the ordering of the hydrogen bonding breaks down in the tetrahedral network of ice with entropy increase, in agreement with the neutron diffraction data. We also calculated the phonon spectra of ice in a 3× 1× 1 supercell using the direct method. So far, due to the direct method used in this calculation, the phonon spectra are obtained without taking into account the effect of polarization arising from dipole–dipole interactions of water molecules, which is expected to yield the splitting of longitudinal and transverse optic modes at the Γ point. The calculated longitudinal acoustic velocities from the initial slopes of the acoustic mode are in reasonable agreement with the neutron scattering data. Analysis of the vibrational density of states shows the existence of a boson peak at low energy of the translational region, a characteristic common to amorphous systems. 相似文献
18.
The electronic structure, elastic constants and lattice dynamics of the B(2) type intermetallic compound LaAg are studied by means of density functional theory calculations with the generalized gradient approximation for exchange and correlation. The calculated equilibrium properties and elastic constants agree well with available experimental data. From the ratio between the bulk and shear moduli, LaAg is found to be ductile, which is unusual for B(2) type intermetallics. The computed band structure shows a dominant contribution from La 5d states near the Fermi level. The phonon dispersion relations, calculated using density functional perturbation theory, are in good agreement with available inelastic neutron scattering data. Under pressure, the phonon dispersions develop imaginary frequencies, starting at around 2.3 GPa, in good accordance with the martensitic instability observed above 3.4 GPa. By structural optimization the high pressure phase is identified as orthorhombic B(19). 相似文献
19.
J. Sjakste V. Tyuterev N. Vast 《Applied Physics A: Materials Science & Processing》2007,86(3):301-307
Interactions between excited electrons and short-wavelength (intervalley) phonons in GaAs are studied using density functional
theory for the conduction bands, and density functional perturbation theory for phonon frequencies and matrix elements of
the electron–phonon interaction. We have calculated the deformation potentials (DPs) and the average intervalley scattering
time 〈τ〉. The integration of the scattering probabilities over all possible final states in the Brillouin zone has been performed
without any ad hoc assumption about the behavior of the electron–phonon matrix elements nor the topology of the conduction
band. For transitions from the L point to Γ valley (within the first conduction band), we find 〈τ〉L to be 1.5 ps at 300 K, in good agreement with time-resolved photoluminescence experiment. We discuss the difference between
our calculated DPs, and effective parameters used in Monte Carlo simulations of optical and transport properties of semiconductors.
The latter are based on Conwell’s model, in which electron–phonon interaction is described by one single constant and a parabolic
model is used for conduction bands. We deduce the effective DP from our 〈τ〉, and compare it to our calculated DPs. We conclude
that only effective DPs obtained from a full calculation of 〈τ〉 are relevant parameters for Monte Carlo simulations.
PACS 71.10-w; 72.10.Di; 71.55.Eq 相似文献
20.
P.T. Jochym K. Parlinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):265-268
Ab initio calculations and a direct method are applied to derive the phonon dispersion relations and phonon density of states for the
ZrC crystal. The results are in good agreement with neutron scattering data. The force constants are determined from the Hellmann-Feynman
forces induced by atomic displacements in a 222 supercell. The elastic constants are found using the deformation method and successfully compare with experimental data.
Received 2 July 1999 and Received in final form 26 November 1999 相似文献