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11.
Viscosity is one of the fundamental physical properties of liquids; for different melts it varies in an extremely wide range. Selenium is among the first elementary substances to have manifested, at compression, a phase transformation in the liquid state accompanied by melt metallization. Direct measurements by means of a real-time radiography show that the viscosity of liquid Se under pressure drops by 500 times to a very low level of 8 mPa s. This is the first case of viscosity measurements being performed both for a relatively viscous semiconducting state and a low-viscous metallic state of the same liquid substance. The viscosity of the Se melt strongly decreases with pressure along the melting curve in a semiconducting state and experiences a further significant drop at melt metallization. A similar phenomenon is expected to be observed in many chalcohenide, halogenide, and oxide melts. 相似文献
12.
Abstract The bulk amorphous tetrahedral semiconductors (Si, Ge. Si0.89(GaAs)0.11, Ge1?x(GaSb)x (0.12<X<I)) were obtained using solid state amorphization. The disordering process occurs at the decompression of high pressure phases Si II, Gell at low temperatures and of solid solutions Sill: GaAs, GeII: GaSb at room temperature. The structure and stability of the obtained phases were investigated 相似文献
13.
Abstract In the melts of Te, Se, S, I2 and Mg3Bi2 the nonmetal-metal transitions were found under pressure. The transitions are accompanied by a decrease of the volume. The transitions seem to terminate at high temperature by “critical regions”. For S and Se the kinetics of the transitions and the pressure influence on the solidification of the melts were investigated. The existence of the transitions of this kind gives an explanation of anomalies of melting curves of some substances. 相似文献
14.
V. V. Brazhkin 《JETP Letters》1998,68(6):502-508
Measurements are made of the average size of the crystallites in Fe samples obtained by rapid quenching from the melt at high
pressures up to 95 kbar. The data obtained make it possible to estimate the pressure dependence of the viscosity of the Fe
melt. It is found that, contrary to the existing empirical models, the viscosity increases along the melting curve under compression.
Extrapolation of the pressure dependences obtained to the P, T conditions corresponding to the Earth’s core gives extremely high values of the viscosity, ranging from 102 Pa·s up to 1011 Pa·s in the outer core, which suggests that the inner core is in a glassy state. The possibility that the lines of vitrification
and melting of substances intersect in the megabar range is discussed.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 469–474 (25 September 1998) 相似文献
15.
V. V. Brazhkin Y. Katayama A. G. Lyapin S. V. Popova Y. Inamura H. Saitoh W. Utsumi 《JETP Letters》2005,82(11):713-718
The results of investigating the phase diagrams of ZnCl2 and AlCl3 halides, as well as the structure of the shortrange order of the corresponding melts under pressures up to 6.5 GPa, by the method of energy-dispersive x-ray diffraction are reported. When a ZnCl2 crystal is compressed, a phase transition occurs from the γ phase (HgI2 structure type) to the δ phase (distorted CdI2 structure, WTe2 type). The structural studies of the liquid state of ZnCl2 and AlCl3 indicate that the intermediate-range order decreases rapidly in the tetrahedral network of both melts as the pressure increases to 1.8 and 2.3 GPa for ZnCl2 and AlCl3, respectively. With further compression, the transitions in both melts occur with a change in the structure of the short-range order and with an increase in the coordination number. In this case, the transition in AlCl3 occurs at ≈4 GPa and is a sharp first order transition, whereas the transition in ZnCl2 occurs more smoothly in a pressure range of 2–4 GPa with a maximum intensity near 3 GPa. Thus, the AlCl3 and ZnCl2 compounds exemplify the existence of two phenomena—gradual decay of intermediate-range structural correlations and a sharper liquid-liquid coordination transition. 相似文献
16.
Abstract In molten iodine two transitions accompanied by a large increase of conductivity (σ) were found under pressure between 3 and 4 GPa. During the first transition a increases by approximately 10′ times, the volume changing very slightly or remaining constant. During the second transition a increases by 2-10 times and then is accompanied by a decrease of volume. 相似文献
17.
Physics of the Solid State - Using the X-ray diffraction and electron microscopy methods, the structure and the elemental and phase compositions of hypereutectic alloy Al86Ni2Co6Gd6 (hereinafter,... 相似文献
18.
JETP Letters - High-precision studies of Raman scattering on isotopically pure 70Ge and 74Ge single crystals have been performed in the temperature range from 80 to 296 K. It has been found that a... 相似文献
19.
V. V. Brazhkin S. G. Lyapin I. A. Trojan R. N. Voloshin A. G. Lyapin N. N. Mel’nik 《JETP Letters》2000,72(4):195-198
Second-order Raman spectra corresponding to transverse acoustic phonons are studied in detail for crystalline Si over the temperature range 20–620°C. The largest relative softening and anharmonicity at the boundaries of the Brillouin zone were observed for the TA(X) mode. Extrapolation of the TA(X) frequency to high temperatures suggests that the Si lattice should be dynamically unstable at temperatures on the order of a doubled melting temperature. It is found that the main contribution to the softening of the transverse acoustic phonons in silicon comes from the anharmonicity and not from the volume expansion. 相似文献
20.
V. V. Brazhkin E. Bychkov O. B. Tsiok 《Journal of Experimental and Theoretical Physics》2017,125(3):451-464
High-precision studies of the volume and the electrical resistivity of g-As2Te3 glasses at a high hydrostatic pressure up to 8.5 GPa at room temperature are performed. The glasses exhibit elastic behavior in compression only at a pressure up to 1 GPa, and a diffuse structural transformation and inelastic density relaxation (logarithmic in time) begin at higher pressures. When the pressure increases further, the relaxation rate passes through a sharp maximum at 2.5 GPa, which is accompanied by softening the relaxing bulk modulus, and then decreases, being noticeable up to the maximum pressure. When pressure is relieved, an unusual inflection point is observed in the baric dependence of the bulk modulus near 4 GPa. The polyamorphic transformation is only partly reversible and the residual densification after pressure release is 2%. In compression, the electrical resistivity of the g-As2Te3 glasses decreases exponentially with increasing pressure (at a pressure up to 2 GPa); then, it decreases faster by almost three orders of magnitude in the pressure range 2–3.5 GPa. At a pressure of 5 GPa, the electrical resistivity reaches 10–3 Ω cm, which is characteristic of a metallic state; this resistivity continues to decrease with increasing pressure and reaches 1.7 × 10–4 Ω cm at 8.1 GPa. The reverse metal–semiconductor transition occurs at a pressure of 3 GPa when pressure is relieved. When the pressure is decreased to atmospheric pressure, the electrical resistivity of the glasses is below the initial pressure by two–three orders of magnitude. Under normal conditions, both the volume and the electrical resistivity relax to quasi-equilibrium values in several months. Comparative structural and Raman spectroscopy investigations demonstrate that the glasses subjected to high pressure have the maximum chemical order. The glasses with a higher order have a lower electrical resistivity. The polyamorphism in the As2Te3 glasses is caused by both structural changes and chemical ordering. The g-As2Te3 compound is the first example of glasses, where the reversible metallization under pressure has been studied under hydrostatic conditions. 相似文献