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1.
R.?MoretEmail author P.?Launois T.?W?gberg B.?Sundqvist V.?Agafonov V.?A.?Davydov A.?V.?Rakhmanina 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,37(1):25-37
We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 single-crystals treated at high-pressure and high-temperature. This allowed us to obtain structural information on the C60 dimer state which can be considered as an intermediate state in the polymerization process. In the 1-6 GPa pressure range the crystals are primarily formed of dimers with additional minor fractions of monomers, 1D and 2D polymers, as shown by the analysis of the Raman spectra. The dimers are disordered within an average cubic lattice derived from that of the monomer. Single-crystal diffraction patterns reveal a characteristic diffuse scattering intensity distribution which has been simulated by calculating the diffuse scattering produced by dimer and trimer model structures. Satisfactory agreement is obtained for random positional and orientational disorder of the C60-C60 dimers although a small concentration of similarly disordered trimers is likely. In a first approximation the dimer/trimer disorder can be considered as random but various inter-dimer correlations are probably present, as discussed.Received: 3 October 2003, Published online: 19 February 2004PACS:
61.48. + c Fullerenes and fullerene-related materials - 61.43.Bn Structural modeling: serial-addition models, computer simulation - 78.30.Na Fullerenes and related materialsT. Wågberg: Present address: Groupe de Dynamique des Phases Condensées, Université Montpellier II, Place E. Bataillon, CC026, 34095 Montpellier, France 相似文献
2.
V. A. Davydov A. A. Shiryaev A. V. Rakhmanina V. P. Filonenko A. L. Vasil’ev C. Autret V. N. Agafonov V. N. Khabashesku 《JETP Letters》2009,90(12):763-767
The solid-phase transformations of polyhedral nanoparticles at a pressure of 8.0 GPa and various temperatures have been investigated by X-ray diffraction, small-angle X-ray scattering, and transmission electron microscopy. It has been found that the graphene layers of the inner cavities of polyhedral particles are transformed into onion-like structures at temperatures above ~1000°C. This transformation gives rise to the formation of hybrid-type sp2 carbon nanoparticles, which combine the outer polyhedral shape with the quasispherical onion-like core. Polyhedral nanoparticles smaller than ~40 nm are completely transformed into onion-like particles at 1600°C. 相似文献
3.
R Nirmala V Sankaranarayanan K Sethupathi AV Morozkin T Geethakumary Y Hariharan 《Pramana》2002,58(5-6):1101-1104
New R
2Ti3Ge4 (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac
magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize
in the parent, Sm5Ge4-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series.
The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales
with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays
a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects. 相似文献
4.
The shift of the Curie temperature of CrO2 with pressure was determined by ac-susceptibility measurements under hydrostatic pressure up to 5 GPa. These experiments show that ferromagnetism of CrO2 is suppressed at a rate , which is close to recent theoretical estimates. 相似文献
5.
A stochastic model of an epidemic is investigated, taking account of the removal of ill members of the population (by death, by recovery with immunization, by isolation) and natural immunization. Limiting distributions are found for the size of the epidemic, the number immunized
1, and their sum, under the assumption that the original number of susceptible individuals n and the number of ill individuals m , while n 1,n
0< , where and are the coefficients for the contraction of the disease and of immunization respectively.Translated from Matematicheskie Zametki, Vol. 8, No. 3, pp. 385–392, September, 1970. 相似文献
6.
A. N. Utyuzh Yu. A. Timofeev A. V. Rakhmanina 《Journal of Experimental and Theoretical Physics》2007,104(4):562-568
The raman scattering technique is used for studying diamonds with a 0.04–0.1 at % boron impurity under a pressure up to 3 GPa in a chamber with sapphire anvils. The Raman frequency increases linearly with pressure for all samples with pressure coefficients of 2.947 cm?1/GPa for pure diamond and 3.01 cm?1/GPa for boron-doped samples. The Raman linewidths remain unchanged for pure diamond and for diamond with a boron concentration of about 0.04 at % and decrease linearly upon an increase in pressure for samples with a boron concentration of about 0.1 at %. The Raman spectra with a line profile corresponding to the Fano resonance do not change qualitatively up to a pressure of 3 GPa. In diamond samples with a boron impurity exceeding 0.1 at %, the boron concentration in the surface layer can be substantially higher than at the center of the sample. 相似文献
7.
V. A. Davydov L. S. Kashevarova A. V. Rakhmanina V. M. Senyavin O. P. Pronina N. N. Oleinikov V. Agafonov H. Szwarc 《JETP Letters》2000,72(11):557-560
Dimerization kinetics was studied for fullerene C60 by IR spectroscopy at a pressure of 1.5 GPa in the temperature range 373–473 K. The kinetic curves for the formation of a dimer (C60)2 were obtained using its analytical IR band at 796 cm?1. Under the assumption that pressure-induced C60 dimerization is a second-order irreversible reaction, the reaction rate constants were determined at different temperatures. The corresponding activation energy and preexponential factor were found to be 134±6 kJ/mol and (1.74± 0.24)×1014 s?1, respectively. The specific features of the solid-phase C60 dimerization in simple cubic and face-centered cubic fullerite phases are discussed. 相似文献
8.
Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta0.33V0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV2. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase. 相似文献
9.
V. A. Davydov L. S. Kashevarova A. V. Rakhmanina A. V. Dzyabchenko V. N. Agafonov P. Dubois R. Ceolin H. Szwarc 《JETP Letters》1997,66(2):120-125
It is established by x-ray diffraction and Raman scattering that the polymerization of C60 fullerene at 1.5 GPa and 723 K leads to the formation of an orthorhombic phase that is different from the previously identified
high-pressure orthorhombic phase. It is determined by a calculation of the optimal packing of linear C60 polymers by the method of atom-atom potentials that the energetically favorable structure of the orthorhombic phase belongs
to the space group P n n m and not the previously proposed group I m m m. The computed value of the rotation angle of the polymer chains that corresponds to the minimum packing energy was equal
to 61°. The mechanisms leading to the formation of the polymerized phases are discussed on the basis of the results obtained.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 2, 110–114 (25 July 1997) 相似文献
10.
Davydov V. A. Shiryaev A. A. Rakhmanina A. V. Filonenko V. P. Vasil’ev A. L. Autret C. Agafonov V. N. Khabashesku V. N. 《JETP Letters》2010,90(12):763-767
JETP Letters - The solid-phase transformations of polyhedral nanoparticles at a pressure of 8.0 GPa and various temperatures have been investigated by X-ray diffraction, small-angle X-ray... 相似文献