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1.
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
2.
The crystal structure and phonon spectrum of PrFe3(BO3)4 are ab initio calculated in the context of the density functional theory. The ion coordinates in the unit cell of a crystal and the lattice parameters are evaluated from the calculations. The types and frequencies of the fundamental vibrations, as well as the line intensities of the IR spectrum, are determined. The elastic constants of the crystal are calculated. A “seed” frequency of the vibration strongly interacting with the electron excitation on the praseodymium ion is obtained for low-frequency A2 mode. The calculated results are in agreement with the known experimental data. 相似文献
3.
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
4.
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
5.
Q. Zhang J. Yang X. Wu S. Qin 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(1):11-16
An investigation into the high-pressure behavior of Sc2O3 was
conducted using first-principle calculations based on density functional theory within the
generalized gradient approximation. Nine candidate phases were considered and simulated,
C-, B-, A-RES, Rh2O3(II), Gd2S3,
U2S3, Al2Er3, corundum and PPv respectively.
Our results demonstrate phase transitions of Sc2O3 from C- to B-RES
phase at 15 GPa, then to Gd2S3 phase at 18 GPa. Elastic constants of
Sc2O3 present softening from about 270 GPa to 337 GPa, associated
with a semiconductor-to-metal crossover. The Gd2S3-type
Sc2O3 is both mechanically and dynamical stable at least up to
302 GPa supported by the mechanically stable criteria and the phonon spectrum. 相似文献
6.
This paper reports the lattice dynamical study of the UGe2 using a lattice dynamical model theory based on pairwise interactions under the framework of the shell model. The calculated
phonon dispersion curves and phonon density of states are in good agreement with the measured data.
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7.
Using first-principles calculations, we have studied the structural, lattice dynamical and thermodynamical properties of the recently synthesized Re2N and Re3N compounds. The generalized gradient approximation is used to model exchange-correlation effects. The phonon dispersion curves are derived using the direct method. The calculated equilibrium lattice parameters are in overall agreement with the available experimental and theoretical results. The present phonon dispersion results show that both compounds are dynamically stable for the structures considered. The temperature-dependent behavior of thermodynamical properties, such as free energy, entropy, heat capacity, and internal energy, is also presented. 相似文献
8.
9.
We have investigated the structural and lattice dynamical properties of XB2(X=Sc,V,Ti) by using first-principles total energy calculations. Specifically, the lattice parameters (a, c) of the stable phase, the bond lengths of X–B and B–B atoms, phonon dispersion curves and the corresponding density of states, and some thermodynamical quantities such as internal energy, entropy, heat capacity, and their temperature-dependent behaviours, are presented. The obtained results for structural parameters are in good agreement with the available experimental and other theoretical studies. 相似文献
10.
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
11.
The ab initio calculations have been carried out for the crystal structure and Raman spectrum of a single crystal of lutetium pyrosilicate Lu2Si2O7. The types of fundamental vibrations and their frequencies and intensities in the Raman spectrum for two polarizations of the crystal have been determined. The calculations have been performed within the framework of the density functional theory (DFT) using the hybrid functionals. The ions involved in the vibrations have been identified using the method of isotopic substitution. The results of the calculations are in good agreement with the experiment. 相似文献
12.
The results of ab initio calculations of the electronic structure, vibrational properties, and the magnetoelectric effect in the La2CuTiO6 crystal with double perovskite structure are presented. The lattice dynamics calculation shows the presence of unstable modes in the phonon spectrum of the high-symmetry cubic phase with space group \(Fm\overline 3 m\). Condensation of two most unstable modes belonging to the center and the boundary point X of the Brillouin zone leads to the formation of a nonpolar stable phase with space group P21/n. The calculation taking into account spin polarization shows that the magnetic ground state is E*-type antiferromagnetic with doubled magnetic cell and with the two spin-up and two spin-down configuration of magnetic moments of copper ions along the [010] crystallographic direction. Such ordering of magnetic moments leads to polar space group and polarization formation. The polarization magnitude is estimated as 71 μC/m2. 相似文献
13.
The elastic, dynamical, and electronic properties of cubic LiHg and Li3Hg were investigated based on first-principles methods. The elastic constants and phonon spectral calculations confirmed the mechanical and dynamical stability of the materials at ambient conditions. The obtained elastic moduli of LiHg are slightly larger than those of Li3Hg. Both LiHg and Li3Hg are ductile materials with strong shear anisotropy as metals with mixed ionic, covalent, and metallic interactions. The calculated Debye temperatures are 223.5 K and 230.6 K for LiHg and Li3Hg, respectively. The calculated phonon frequency of the T2g mode in Li3Hg is 326.8 cm?1. The p states from the Hg and Li atoms dominate the electronic structure near the Fermi level. These findings may inspire further experimental and theoretical study on the potential technical and engineering applications of similar alkali metal-based intermetallic compounds. 相似文献
14.
Venu MankadHimadri R. Soni Sanjeev K. GuptaPrafulla K. Jha 《Physica B: Condensed Matter》2011,406(19):3599-3604
We present results of first principles total energy calculations of the structure, electronic and lattice dynamics for beryllium semiboride and its three ternary alloys using generalized gradient and local density approximations under the framework of density functional theory. The generalized gradient approximation is used for all compounds except MgBeB using the Perdew-Burke-Ernzehorf exchange correlation functional while local density approximations use the Perdew-Zunger ultrasoft exchange correlation functional. The calculated ground state structural parameters are in good agreement with those of experimental and previous theoretical studies. The electronic band structure calculations show that Be2B may transform to a semiconductor after Al substitution. A linear response approach to density functional theory is used to calculate phonon dispersion curves and vibrational density of states. The phonon dispersion curves of Be2B and AlBeB are positive indicating a dynamical stablility of the structure for these compounds. The phonon dispersion curves of NaBeB and MgBeB show the imaginary phonons throughout the Brillouin zone, which confirms dynamical instability as indicated in band structures for these alloys. We also present the partial phonon density of states for different species of Be2B and AlBeB to bring out the details of the participation of different atoms in the total phonon density of state, particularly the role played by Al atom. The first time calculated phonon properties are clearly able to bring out the significant effect of isoelectronic substitution in Be2B. 相似文献
15.
B. Pedrini S. Wessel J. L. Gavilano H. R. Ott S. M. Kazakov J. Karpinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):219-228
We report results of susceptibility χ and 7Li NMR measurements on LiVSi2O6. The temperature dependence of the magnetic susceptibility χ(T) exhibits a broad maximum, typical for low-dimensional magnetic
systems. Quantitatively it is in agreement with the expectation for an S=1 spin chain, represented by the structural arrangement
of V ions.
The NMR results indicate antiferromagnetic ordering below TN=24 K. The intra- and interchain coupling J and Jp for LiVSi2O6, and also for its sister compounds LiVGe2O6, NaVSi2O6 and NaVGe2O6, are obtained via a modified random phase approximation which takes into account results of quantum Monte Carlo calculations.
While Jp is almost constant across the series, J varies by a factor of 5, decreasing with increasing lattice constant along the chain
direction. The comparison between experimental and theoretical susceptibility data suggests the presence of an easy-axis magnetic
anisotropy, which explains the formation of an energy gap in the magnetic excitation spectrum below TN, indicated by the variation of the NMR spin-lattice relaxation rate at T≪TN. 相似文献
16.
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
17.
Y. Yan J. Y. Zhang T. Cui Y. Li Y. M. Ma J. Gong Z. G. Zong G. T. Zou 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):397-403
The lattice dynamics of lithium nitride (Li3N) under high pressure are extensively investigated to probe its phase transformations by using the pseudopotential plane-wave
method within the density functional theory. A new second order α↦α′-Li3N phase transition is identified for the first time. The newly proposed α′-phase possesses a hexagonal symmetry with four ions in the unit cell having a space group of P-3m1. Further enthalpy and
phonon calculations support the existence of this phase, which stabilizes in a narrow pressure range of 2.8 – 3.6 GPa at zero
temperature. Upon further compression, transitions to denser packed phases of β-and γ-Li3N are typical first order. The analysis of the electronic densities of states suggests that all the high pressure modifications
of Li3N are insulators and, interestingly, the typical behavior of compression is to broaden the band gap. 相似文献
18.
采用基于密度泛函理论的平面波赝势方法,在局域密度近似下采用线性响应的密度泛函微扰理论计算了LiNH2的晶格动力学、介电性质和热力学性质,得到了布里渊区高对称方向上的声子色散曲线和相应的声子态密度,分析了 LiNH2的红外和拉曼活性声子频率,同时给出它的介电张量和玻恩有效电荷张量. 研究表明,LiNH2存在小的各向异性,计算所得结果与实验值和其他理论值符合较好.最后,利用得到的声子态密度进一步预测了LiNH2的热力学性质
关键词:
密度泛函理论
晶格动力学
热力学性质
第一性原理计算 相似文献
19.
A. G. Gamzatov A. M. Aliev Sh. B. Abdulvagidov A. B. Batdalov O. Yu. Gorbenko 《Russian Physics Journal》2007,50(4):383-386
Temperature dependences (77–300 K) of the thermal capacity, diffusion, and conductivity are investigated for the Nd
0.5
Sr
0.5
MnO
3 and Nd
0.55
Sr
0.45
MnO
3 polycrystalline samples. The examined characteristics show anomalous behavior in the magnetic phase transition and transition
to the charge-ordered state. It is demonstrated that the main reason for a sharp decrease in the thermal conductivity during
Nd
0.5
Sr
0.5
MnO
3 transition into the antiferromagnetic charge-ordered state is a change in the phonon spectrum caused by the lattice compression.
A temperature dependence of the free phonon path is calculated for the examined temperature interval based on the thermal
diffusion obtained and the literature data on the sound propagation velocity.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 72–75, April, 2007. 相似文献
20.
A lattice dynamical study of the geophysically important mineral MgSiO3 in its orthorhombic perovskite phase, with space group Pnma (D 2h 16 ) has been carried out using a rigid ion model, with the potential consisting of Coulombic and short-ranged interactions. With the help of program DISPR, the ionic charges and radii were optimized using the equilibrium conditions. The resulting potential model is employed to predict the elastic constants and the phonon dispersion relations. The computed long wavelength optic modes are in good agreement with the corresponding experimental Raman and infrared active bands. The phonon density of states has been obtained and is used to evaluate the specific heat, the mean square displacements and thermal parameters of atoms. 相似文献