排序方式: 共有97条查询结果,搜索用时 578 毫秒
71.
72.
73.
Abstract In the melts of Se S and I2 the nonmetal-metal transitions were found under pressure. For sulphur and selenium the transitions are accompanied by a decrease of the volume. For iodine two transitions take place. During the first one the volume changes very slightly, the second transition being accompanied by an essential decrease of the volume. The existence of transitions of this kind gives an explanation for anomalies in the melting curves of some substances. 相似文献
74.
Calcium at megabar pressures undergoes numerous structural transitions and has a complex phase diagram. At the same time, according to the recent theoretical investigations, an anomalous behavior of many physical properties, including a transition to the state of a narrow-gap semiconductor, can be expected even in the region of stability of the normal-pressure phase of calcium with the fcc structure at moderate pressures P ~ 5–15 GPa. Data on the thermopower of calcium in the pressure range up to 9 GPa have been reported. The thermopower in this pressure range is positive, has a smooth maximum at 5–6 GPa, and decreases quite rapidly at higher pressures. The absolute values of the thermopower (5–12 μV/K) indicate that calcium in this pressure range is a metal. The difference between the thermopowers in the direct and inverse passages in the range of 5–7.5 GPa is fairly noticeable (~10%). The possible reasons for such an anomalous behavior, as well as new calculations of the band structure of calcium, have been discussed. 相似文献
75.
E. L. Gromnitskaya O. V. Stal'gorova A. G. Lyapin V. V. Brazhkin O. B. Tarutin 《JETP Letters》2003,78(8):488-492
Nonequilibrium phase transformations in D2O ices, including the solid-state amorphization of ice 1h (1h-hda) and the heating-induced transition cascade hda-lda-1c-1h from high-density amorphous (hda) ice to low-density amorphous (lda) ice followed by crystallization in cubic ice 1c and phase transition to ordinary hexagonal ice 1h, were studied using an ultrasonic technique. It has been shown that, as in H2O ice, the softening of a crystal lattice or an amorphous network precedes nonequilibrium transformations. However, noticeable isotopic differences in the behavior of the elastic properties of H2O and D2O, in particular, their 1h and hda modifications, call for a more detailed study of the structural features of these H2O and D2O phases. 相似文献
76.
Dianov EM Mashinsky VM Neustruev VB Sazhin OD Brazhkin VV Sidorov VA 《Optics letters》1997,22(14):1089-1091
Spectroscopic properties of germanium oxygen-deficient centers were studied in vapor axial deposition and modified chemical-vapor deposition germanosilicate glass after hydrostatic densification by as much as 19%. Gaussian decomposition showed a broadening and a significant shift of the initial absorption bands at 5.11 and 5.42 eV. A threefold decrease of the 3.15-eV luminescence band was revealed, whereas the 4.25-eV luminescence band was only slightly sensitive to densification. This shows that these two bands belong to different luminescence centers. A drastic growth of a new metastable absorption band near 7.3 eV was observed. The pressure-induced changes disappeared as a result of thermal annealing. These changes are discussed with respect to in-fiber grating phenomena. 相似文献
77.
Brazhkin VV Katayama Y Trachenko K Tsiok OB Lyapin AG Artacho E Dove M Ferlat G Inamura Y Saitoh H 《Physical review letters》2008,101(3):035702
We study high-pressure polyamorphism of B2O3 glass using x-ray diffraction up to 10 GPa in the 300-700 K temperature range, in situ volumetric measurements up to 9 GPa, and first-principles simulations. Under pressure, glass undergoes two-stage transformations including a gradual increase of the first B-O (O-B) coordination numbers above 5 GPa. The fraction of boron atoms in the fourfold-coordinated state at P<10 GPa is smaller than was assumed from inelastic x-ray scattering spectroscopy data, but is considerably larger than was previously suggested by the classical molecular dynamics simulations. The observed transformations under both compression and decompression are broad in hydrostatic conditions. On the basis of ab initio results, we also predict one more transformation to a superdense phase, in which B atoms are sixfold coordinated. 相似文献
78.
P. A. Borisova M. S. Blanter V. V. Brazhkin M. M. Murashev V. A. Somenkov V. P. Filonenko 《Bulletin of the Russian Academy of Sciences: Physics》2017,81(11):1330-1335
The effect deuterium has on phase transformations is studied for amorphous and crystalline fullerenes C60 and C70 at high temperatures of up to 1300°C and high pressures (2–8 GPa). Amorphous fullerene phases are obtained via long grinding in a planetary mill. Structure is studied by means of neutron diffraction. In all cases, amorphous graphite (nanographite) forms in the temperature range of 800–1100°C. This material has different diffraction spectra distinguished by the heights of the halos observed on the graphite diffraction maxima and their relative intensities. These spectra (the structure of nanographite) are affected by preliminary amorphization, the number of carbon atoms in the fullerenes (C60 or C70), and the introduction of deuterium atoms. The different spectra of amorphous (disordered) graphite testify to its varying structure. 相似文献
79.
An ultrasonic investigation of pressure-induced direct and reverse transformations lda-hda between the amorphous phases of low-and high-density ice is performed and the change in the shear modulus is determined.
It is found that elastic softening of the amorphous network precedes both transformations, and the behavior of lda phase is similar to that of hexagonal 1h ice before amorphization. At the same time a number of features of the lda-hda transformation are due to the topological disordering of the amorphous phases, and the kinetics of the transformation is
different from the standard behavior at a first-order phase transition and also from the compression kinetics of “ classic”
glasses of the type a-SiO2 and a-GeO2. It is shown that the difference in the behavior of the lda and hda amorphous phases under pressure can be attributed to characteristic features of their spectra of low-energy two-level states.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 653–658 (10 May 1999) 相似文献
80.
N. E. Sluchanko V. V. Glushkov S. V. Demishev M. V. Kondrin N. A. Samarin V. V. Brazhkin I. Braunserade V. V. Moshchalkov 《Physics of the Solid State》1999,41(1):1-7
Galvanomagnetic characteristics of the A1−x
Six solid solutions (x<12 at. %) have been studied within a broad range of temperatures (1.8–290 K) and magnetic fields (up to 15 T). An anomaly
in the concentration dependence of the Hall coefficient R
H
(x,T=290 K) has been revealed near the boundary of absolute instability (x<8.5 at. %) of compounds in the Al1−x
Six series. The variation of the Hall coefficient and of the magnetoresistance in the A1−x
Six series at low (T<77 K) temperatures is analyzed within models taking into account the anisotropy in conduction-band electron scattering.
Fiz. Tverd. Tela (St. Petersburg) 41, 3–10 (January 1999) 相似文献